HOME

TheInfoList




In
biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, Development ...

biology
and
biochemistry Biochemistry or biological chemistry, is the study of es within and relating to living s. A sub-discipline of both and , biochemistry may be divided into three fields: , and . Over the last decades of the 20th century, biochemistry has beco ...

biochemistry
, a lipid is a macro
biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a Nobel Prize in Chemistry, Nobel Prize i ...
that is soluble in
nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...
solvents. Non-polar solvents are typically
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
s used to dissolve other naturally occurring hydrocarbon lipid
molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...

molecule
s that do not (or do not easily) dissolve in water, including
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s,
wax Waxes are a diverse class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, ...
es,
sterol Sterol is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and synth ...

sterol
s, fat-soluble
vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...
s (such as vitamins A, D, E, and K),
monoglyceride Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two different ...

monoglyceride
s,
diglyceride A diglyceride, or diacylglycerol (DAG), is a glyceride , the simplest possible fat after Triformin Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic. Glycer ...
s,
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
s, and
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s. The functions of lipids include storing energy,
signaling In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, images, and scientific measurements. Sig ...
, and acting as structural components of
cell membrane cell membrane vs. Prokaryotes A prokaryote is a typically unicellular organism that lacks a nuclear membrane-enclosed cell nucleus, nucleus. The word ''prokaryote'' comes from the Greek language, Greek (, 'before') and (, 'nut' or 'kernel').C ...

cell membrane
s. Lipids have applications in the cosmetic and food industries as well as in
nanotechnology Nanotechnology, also shortened to nanotech, is the use of matter on an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...

nanotechnology
. Scientists sometimes define lipids as
hydrophobic In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of at ...
or
amphiphilic An amphiphile (a.k.a. amphipath; from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
small molecules; the amphiphilic nature of some lipids allows them to form structures such as
vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features of ...
, multilamellar/
unilamellar liposome A unilamellar liposome is a spherical chamber/vesicle, bounded by a single bilayer of an amphiphilic lipid or a mixture of such lipids, containing aqueous solution inside the chamber. Unilamellar liposomes are used to study biological systems and to ...
s, or membranes in an aqueous environment. Biological lipids originate entirely or in part from two distinct types of biochemical subunits or "building-blocks": ketoacyl and
isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals (including humans) and i ...

isoprene
groups. Using this approach, lipids may be divided into eight categories:
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s,
glycerolipid In biology and biochemistry, a lipid is a macro biomolecule that is soluble in Chemical polarity, nonpolar solvents. Chemical polarity#Nonpolar molecules, Non-polar solvents are typically hydrocarbons used to dissolve other naturally occurring ...
s,
glycerophospholipid Examples of variable phosphate esters in glycerophospholipids Glycerophospholipids or phosphoglycerides are glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a co ...

glycerophospholipid
s,
sphingolipid Sphingolipids are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, ...

sphingolipid
s,
saccharolipid Saccharolipids are chemical compounds A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...
s, and
polyketidePolyketides are a large group of secondary metabolites which either contain alternating carbonyl groups and methylene groups (-CO-CH2-), or are derived from precursors which contain such alternating groups. Many polyketides are medicinal or exhibit a ...
s (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits). Although the term "lipid" is sometimes used as a synonym for
fat In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided ...

fat
s, fats are a subgroup of lipids called
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an derived from and three (from ' and '). Triglycerides are the main constituents of in humans and other vertebrates, as well as . They are also present in the blood to enab ...

triglyceride
s. Lipids also encompass molecules such as
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s and their derivatives (including
tri- Numeral or number prefixes are prefix A prefix is an which is placed before the of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates ...

tri-
, di-,
monoglyceride Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two different ...

monoglyceride
s, and
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s), as well as other
sterol Sterol is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and synth ...

sterol
-containing
metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-Europ ...
s such as
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
. Although humans and other mammals use various
biosynthetic pathway Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conv ...

biosynthetic pathway
s both to break down and to synthesize lipids, some essential lipids can't be made this way and must be obtained from the diet.


History

''Lipid may be regarded as organic substances relatively insoluble in water, soluble in organic solvents(alcohol, ether etc.) actually or potentially related to fatty acid and utilized by the living cells.'' In 1815,
Henri Braconnot Henri Braconnot (May 29, 1780, Commercy, Meuse (department), Meuse – January 13, 1855, Nancy, France, Nancy, Meurthe-et-Moselle) was a French people, French chemist and pharmacist. He was born in Commercy, his father being a counsel at the loc ...

Henri Braconnot
classified lipids (''graisses'') in two categories, ''suifs'' (solid greases or tallow) and ''huiles'' (fluid oils). In 1823,
Michel Eugène Chevreul Michel Eugène Chevreul (31 August 1786 – 9 April 1889) was a French chemist whose work influenced several areas in science, medicine, and art. His early work with animal fats revolutionized the manufacture of soap and of candles and led to his ...

Michel Eugène Chevreul
developed a more detailed classification, including oils, greases, tallow, waxes, resins, balsams and volatile oils (or essential oils). The first synthetic triglyceride was reported by
Théophile-Jules Pelouze Image:Théophile-Jules Pelouze.png, Théophile-Jules Pelouze Théophile-Jules Pelouze (also known as Jules Pelouze, Théophile Pelouze, Theo Pelouze, or T. J. Pelouze, ; 26 February 180731 May 1867) was a French chemist. Life He was born at Valog ...

Théophile-Jules Pelouze
in 1844, when he produced by treating
butyric acid Butyric acid (from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is inten ...

butyric acid
with
glycerin Glycerol (; also called glycerine or glycerin) is a simple polyol compound. It is a colorless, odorless, viscous The viscosity of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) und ...

glycerin
in the presence of concentrated
sulfuric acid Sulfuric acid ( and the ) or sulphuric acid (), known in antiquity as oil of vitriol, is a composed of the elements , and , with the . It is a colorless, odorless and liquid that is with water. Pure sulfuric acid does not exist naturally ...

sulfuric acid
. Several years later,
Marcellin Berthelot Pierre Eugène Marcellin Berthelot (; 1827–1907) was a French chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific m ...

Marcellin Berthelot
, one of Pelouze's students, synthesized tristearin and by reaction of the analogous
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s with glycerin in the presence of gaseous
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with ...

hydrogen chloride
at high temperature. In 1827,
William Prout William Prout Fellow of the Royal Society, FRS (; 15 January 1785 – 9 April 1850) was an English chemist, physician, and natural theologian. He is remembered today mainly for what is called Prout's hypothesis. Biography Prout was born in Ho ...
recognized fat ("oily" alimentary matters), along with protein ("albuminous") and carbohydrate ("saccharine"), as an important nutrient for humans and animals. For a century, chemists regarded "fats" as only simple lipids made of fatty acids and glycerol (glycerides), but new forms were described later. Theodore Gobley (1847) discovered phospholipids in mammalian brain and hen egg, called by him as "
lecithin 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; – saturated fatty acid. Lecithin (, from the Greek ''lekithos'' "yolk") ...
s". Thudichum discovered in human brain some phospholipids (
cephalin Phosphatidylethanolamines are a class of phospholipids found in biological membranes. They are synthesized by the addition of cytidine diphosphate-ethanolamine to diglycerides, releasing cytidine monophosphate. S-Adenosyl methionine, ''S''-Adenosyl ...
), glycolipids (
cerebroside Cerebrosides is the common name for a group of glycosphingolipids called monoglycosylceramides which are important components in animal muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are la ...

cerebroside
) and sphingolipids (
sphingomyelin Sphingomyelin (SPH, ˌsfɪŋɡoˈmaɪəlɪn) is a type of sphingolipid Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extrac ...

sphingomyelin
). The terms lipoid, lipin, lipide and lipid have been used with varied meanings from author to author. In 1912, Rosenbloom and Gies proposed the substitution of "lipoid" by "lipin". In 1920, Bloor introduced a new classification for "lipoids": simple lipoids (greases and waxes), compound lipoids (phospholipoids and glycolipoids), and the derived lipoids (fatty acids, alcohols, sterols). The word ''lipide'', which stems etymologically from Greek λίπος, ''lipos'' 'fat', was introduced in 1923 by the French pharmacologist Gabriel Bertrand. Bertrand included in the concept not only the traditional fats (glycerides), but also the "lipoids", with a complex constitution. Even though the word ''lipide'' was unanimously approved by the international commission of the ''Société de Chimie Biologique'' during the plenary session on the July 3, 1923. The word ''lipide'' was later anglicized as ''lipid'' because of its pronunciation ('lɪpɪd). In French, the suffix ''-ide'', from Ancient Greek -ίδης (meaning 'son of' or 'descendant of'), is always pronounced (ɪd). In 1947, T. P. Hilditch divided lipids into "simple lipids", with greases and waxes (true waxes, sterols, alcohols).


Categories

Lipids have been classified into eight categories by the
Lipid MAPS LIPID MAPS (Lipid Metabolites and Pathways Strategy) is a web portal designed to be a gateway to Lipidomics resources. The resource has spearheaded a classification of biological lipids, dividing them into eight general categories. LIPID MAPS provi ...
consortium as follows:


Fatty acids

Fatty acids In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in ...
, or fatty acid residues when they are part of a lipid, are a diverse group of molecules synthesized by chain-elongation of an
acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reaction Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organism In biology, an organism (from ...

acetyl-CoA
primer with
malonyl-CoA Malonyl-CoA is a coenzyme A Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme A cofactor is a non-protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residue ...

malonyl-CoA
or groups in a process called
fatty acid synthesis Fatty acid synthesis is the creation of fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline invo ...
. They are made of a that terminates with a
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
group; this arrangement confers the molecule with a
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the clim ...
,
hydrophilic A hydrophile is a molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In phys ...
end, and a nonpolar,
hydrophobic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...
end that is
insoluble In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence i ...

insoluble
in water. The fatty acid structure is one of the most fundamental categories of biological lipids and is commonly used as a building-block of more structurally complex lipids. The carbon chain, typically between four and 24 carbons long, may be saturated or unsaturated, and may be attached to
functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions re ...
s containing
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
,
halogen The halogens () are a group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can ...

halogen
s,
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
, and
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
. If a fatty acid contains a double bond, there is the possibility of either a ''cis'' or ''trans''
geometric isomerism Geometry (from the grc, γεωμετρία; '' geo-'' "earth", '' -metron'' "measurement") is, with arithmetic Arithmetic (from the Ancient Greek, Greek wikt:en:ἀριθμός#Ancient Greek, ἀριθμός ''arithmos'', 'number' and wikt ...
, which significantly affects the molecule's
configuration Configuration or configurations may refer to: Computing * Computer configuration or system configuration * Configuration file, a software file used to configure the initial settings for a computer program * Configurator, also known as choice board, ...
. ''Cis''-double bonds cause the fatty acid chain to bend, an effect that is compounded with more double bonds in the chain. Three double bonds in 18-carbon ''
linolenic acid Linolenic acid is a type of fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline involved with Ch ...
'', the most abundant fatty-acyl chains of plant ''thylakoid membranes'', render these membranes highly ''fluid'' despite environmental low-temperatures, and also makes linolenic acid give dominating sharp peaks in high resolution 13-C NMR spectra of chloroplasts. This in turn plays an important role in the structure and function of cell membranes. Most naturally occurring fatty acids are of the ''cis'' configuration, although the ''trans'' form does exist in some natural and partially hydrogenated fats and oils. Examples of biologically important fatty acids include the
eicosanoid Eicosanoids are signaling molecules In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cell (biology), cells and coordinates multiple-cell actions. A signal is an entity th ...
s, derived primarily from
arachidonic acid Arachidonic acid (AA, sometimes ARA) is a polyunsaturated In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''org ...

arachidonic acid
and
eicosapentaenoic acid Eicosapentaenoic acid (EPA; also icosapentaenoic acid) is an omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) ...
, that include
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) ...
s,
leukotriene Note the four double bonds, three of them conjugated. This is a common property of A4, B4, C4, D4, and E4. is a cysteinyl leukotriene, as are D4 and E4. Leukotrienes are a family of eicosanoid Eicosanoids are signaling molecules made by t ...
s, and
thromboxane Thromboxane is a member of the family of lipids In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecula ...
s.
Docosahexaenoic acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that con ...

Docosahexaenoic acid
is also important in biological systems, particularly with respect to sight. Other major lipid classes in the fatty acid category are the fatty esters and fatty amides. Fatty esters include important biochemical intermediates such as
wax ester A wax ester (WE) is an ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a and an . s are s of ; they are important in biology ...
s, fatty acid thioester
coenzyme A Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the Fatty acid metabolism#Synthesis, synthesis and Fatty acid metabolism#.CE.B2-Oxidation, oxidation of fatty acids, and the oxidation of pyruvic acid, pyruvate in the citric ac ...
derivatives, fatty acid thioester ACP derivatives and fatty acid carnitines. The fatty amides include , such as the
cannabinoid Cannabinoids () are compounds found in Cannabis (drug), cannabis. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (Delta9-THC or Delta8-THC), the primary psychoactive drug, psychoactive compound in cannabis. Cannabid ...
neurotransmitter
anandamide Anandamide (ANA), also known as ''N''-arachidonoylethanolamine (AEA), is a fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and ...

anandamide
.


Glycerolipids

Glycerolipids are composed of mono-, di-, and tri-substituted
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
s, the best-known being the fatty acid of glycerol, called
triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) compose ...
. The word "triacylglycerol" is sometimes used synonymously with "triglyceride". In these compounds, the three hydroxyl groups of glycerol are each esterified, typically by different fatty acids. Because they function as an energy store, these lipids comprise the bulk of storage
fat In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided ...

fat
in animal tissues. The hydrolysis of the
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
bonds of triglycerides and the release of glycerol and fatty acids from
adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biolo ...

adipose tissue
are the initial steps in metabolizing fat. Additional subclasses of glycerolipids are represented by glycosylglycerols, which are characterized by the presence of one or more sugar residues attached to glycerol via a
glycosidic linkage A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group ...
. Examples of structures in this category are the digalactosyldiacylglycerols found in plant membranes and seminolipid from mammalian
sperm cells A spermatozoon (pronounced , alternate spelling spermatozoön; plural spermatozoa; from grc, σπέρμα ("seed") and grc, ζῷον ("living being")) is a motile sperm Cell (biology), cell, or moving form of the ploidy, haploid cell (biology), ...
.


Glycerophospholipids

Glycerophospholipids, usually referred to as
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s (though
sphingomyelin Sphingomyelin (SPH, ˌsfɪŋɡoˈmaɪəlɪn) is a type of sphingolipid Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extrac ...

sphingomyelin
s are also classified as phospholipids), are ubiquitous in nature and are key components of the
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electrical charge on one side and a negative charge on another side, which produces the resting pot ...
of cells, as well as being involved in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
and
cell signaling In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
. Neural tissue (including the brain) contains relatively high amounts of glycerophospholipids, and alterations in their composition has been implicated in various neurological disorders. Glycerophospholipids may be subdivided into distinct classes, based on the nature of the polar headgroup at the ''sn''-3 position of the glycerol backbone in
eukaryote Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

eukaryote
s and eubacteria, or the ''sn''-1 position in the case of
archaebacteria Archaea ( ; singular archaeon ) constitute a Domain (biology), domain of Unicellular organism, single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially Taxonomy (biology), classified a ...
. Examples of glycerophospholipids found in
biological membrane A biological membrane, biomembrane or cell membrane is a Semipermeable membrane, selectively permeable membrane that separates Cell (biology), cell from the extracellular, external environment or creates intracellular compartments. Biological mem ...
s are
phosphatidylcholine Phosphatidylcholines (PC) are a class of phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring ...

phosphatidylcholine
(also known as PC, GPCho or
lecithin 300px, An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline and phosphate group; – glycerol; – monounsaturated fatty acid; – saturated fatty acid. Lecithin (, from the Greek ''lekithos'' "yolk") ...
),
phosphatidylethanolamine Phosphatidylethanolamine (PE) is a class of phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurri ...

phosphatidylethanolamine
(PE or GPEtn) and
phosphatidylserine Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other natural ...

phosphatidylserine
(PS or GPSer). In addition to serving as a primary component of cellular membranes and binding sites for intra- and intercellular proteins, some glycerophospholipids in eukaryotic cells, such as
phosphatidylinositol Phosphatidylinositol (or Inositol Phospholipid) consists of a family of lipids as illustrated on the right, where red is x, blue is y, and black is z, in the context of independent variation, a class of the Glycerophospholipid, phosphatidylglyceri ...

phosphatidylinositol
s and
phosphatidic acidPhosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty aci ...

phosphatidic acid
s are either precursors of or, themselves, membrane-derived
second messengers Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intracellular signals, a non-local form or cell signaling, encompassing both first mes ...
. Typically, one or both of these hydroxyl groups are acylated with long-chain fatty acids, but there are also alkyl-linked and 1Z-alkenyl-linked (
plasmalogen Glycerophospholipids Examples of variable phosphate esters in glycerophospholipids Glycerophospholipids or phosphoglycerides are glycerol Glycerol (; also called glycerine or glycerin) is a simple polyol compound. It is a colorless, odorless ...

plasmalogen
) glycerophospholipids, as well as dialkylether variants in archaebacteria.


Sphingolipids

Sphingolipid Sphingolipids are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, ...

Sphingolipid
s are a complicated family of compounds that share a common structural feature, a sphingoid base backbone that is synthesized ''de novo'' from the amino acid
serine Serine (symbol Ser or S) is an α-amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, ...

serine
and a long-chain fatty acyl CoA, then converted into
ceramide Ceramides are a family of wax Waxes are a diverse class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are kn ...
s, phosphosphingolipids, glycosphingolipids and other compounds. The major sphingoid base of mammals is commonly referred to as
sphingosine Sphingosine (2-amino-4-trans-octadecene-1,3-diol) is an 18-carbon amino alcoholAlkanolamines are chemical compounds that contain both hydroxyl (-OH) and amino (-NH2, -NHR, and -NR2) functional groups on an alkane backbone. The term alkanolamine is ...

sphingosine
. Ceramides (N-acyl-sphingoid bases) are a major subclass of sphingoid base derivatives with an
amide In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amide
-linked fatty acid. The fatty acids are typically saturated or mono-unsaturated with chain lengths from 16 to 26 carbon atoms. The major phosphosphingolipids of mammals are
sphingomyelin Sphingomyelin (SPH, ˌsfɪŋɡoˈmaɪəlɪn) is a type of sphingolipid Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extrac ...

sphingomyelin
s (ceramide phosphocholines), whereas insects contain mainly ceramide phosphoethanolamines and fungi have phytoceramide phosphoinositols and
mannose Mannose is a sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosaccharides joine ...

mannose
-containing headgroups. The glycosphingolipids are a diverse family of molecules composed of one or more sugar residues linked via a
glycosidic bond A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate. A glycosidic bond is formed between the hemiacetal or hemiketal group ...
to the sphingoid base. Examples of these are the simple and complex glycosphingolipids such as
cerebroside Cerebrosides is the common name for a group of glycosphingolipids called monoglycosylceramides which are important components in animal muscle Muscle is a soft tissue found in most animals. Muscle cells contain protein Proteins are la ...

cerebroside
s and
ganglioside A ganglioside is a molecule composed of a glycosphingolipidImage:Sphingosine structure.svg, Sphingosine Glycosphingolipids are a subtype of glycolipids containing the amino alcohol sphingosine. They may be considered as sphingolipids with an atta ...
s.


Sterols

Sterol Sterol is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and t ...

Sterol
s, such as
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
and its derivatives, are an important component of membrane lipids, along with the glycerophospholipids and sphingomyelins. Other examples of sterols are the
bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primary b ...
s and their conjugates, which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver. The plant equivalents are the
phytosterols Phytosterols are phytosteroid Phytosteroids, also known as plant steroids, are naturally occurring steroid , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Un ...
, such as
β-sitosterol β-Sitosterol (beta-sitosterol) is one of several phytosterols (plant sterols) with chemical structures similar to that of cholesterol. It is a white, waxy powder with a characteristic odor, and is one of the components of the food additive E499. ...
,
stigmasterol Stigmasterol – a plant sterol ('' phytosterol'') – is among the most abundant of plant sterol Sterol is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, mole ...

stigmasterol
, and ; the latter compound is also used as a
biomarker A biomarker, or biological marker is a measurable indicator Indicator may refer to: Biology * Indicator (genus), ''Indicator'' (genus), a genus of birds in the honeyguide family * Environmental indicator of environmental health (pressures, cond ...
for
algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cel ...

algal
growth. The predominant sterol in
fungal A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungal
cell membranes is
ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol Sterol is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: t ...

ergosterol
. Sterols are
steroid A steroid is a biologically active organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

steroid
s in which one of the hydrogen atoms is substituted with a
hydroxyl group A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...

hydroxyl group
, at position 3 in the carbon chain. They have in common with steroids the same fused four-ring core structure. Steroids have different biological roles as
hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

hormone
s and
signaling molecules In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
. The eighteen-carbon (C18) steroids include the
estrogen Estrogens or oestrogens, are a class of natural or synthetic sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid ho ...

estrogen
family whereas the C19 steroids comprise the
androgen An androgen (from Greek ''andr-'', the stem of the word meaning "man") is any natural or synthetic steroid hormone A steroid hormone is a steroid , hypothetical a steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 c ...
s such as
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and
androsterone Androsterone, or 3α-hydroxy-5α-androstan-17-one, is an endogenous steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adrenal cortex, ...

androsterone
. The C21 subclass includes the
progestogens Progestogens, also sometimes written progestagens or gestagens, are a class of steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adren ...
as well as the
glucocorticoid Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroid Corticosteroids are a class of steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: cor ...
s and
mineralocorticoids Mineralocorticoids are a class of corticosteroid Corticosteroids are a class of steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the adre ...
. The
secosteroid A secosteroid () is a type of steroid with a "broken" ring. The word ''secosteroid ''derives from the Latin verb ''secare'' meaning "to cut", and 'steroid'. Secosteroids are alternatively described as a subclass of steroids; ; or derived from st ...
s, comprising various forms of
vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...
, are characterized by cleavage of the B ring of the core structure.


Prenols

Prenol Prenol, or 3-methyl-2-buten-1-ol, is a natural alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term ...
lipids are synthesized from the five-carbon-unit precursors
isopentenyl diphosphate Isopentenyl pyrophosphate (IPP, isopentenyl diphosphate, or IDP) is an isoprenoid precursor. IPP is an intermediate in the classical, HMG-CoA reductase pathway (commonly called the mevalonate pathway) and in the ''non-mevalonate'' MEP pathway of i ...
and
dimethylallyl diphosphate Dimethylallyl pyrophosphate (DMAPP; or alternatively, dimethylallyl diphosphate (DMADP); also isoprenyl pyrophosphate) is an isoprenoid precursor. It is a product of both the mevalonate pathway and the MEP pathway of isoprenoid precursor biosynth ...

dimethylallyl diphosphate
that are produced mainly via the
mevalonic acid Mevalonic acid (MVA) is a key organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properti ...

mevalonic acid
(MVA) pathway. The simple isoprenoids (linear alcohols, diphosphates, etc.) are formed by the successive addition of C5 units, and are classified according to number of these
terpene Terpenes () are a class of natural product A natural product is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than ...
units. Structures containing greater than 40 carbons are known as polyterpenes.
Carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
s are important simple isoprenoids that function as
antioxidant Antioxidants are compounds Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above ...

antioxidant
s and as precursors of
vitamin A Vitamin A is a group of unsaturated nutritional organic compounds that includes retinol, retinal, (also known as retinaldehyde), retinoic acid and several provitamin A carotenoids (most notably Beta-Carotene, beta-carotene). Vitamin A has mul ...

vitamin A
. Another biologically important class of molecules is exemplified by the
quinone The quinones are a class of organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties ...

quinone
s and
hydroquinone Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), ...

hydroquinone
s, which contain an isoprenoid tail attached to a quinonoid core of non-isoprenoid origin.
Vitamin E Vitamin E is a group of eight fat solubleLipophilicity (from Greek language, Greek λίπος "fat" and :wikt:φίλος, φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solven ...

Vitamin E
and
vitamin K Vitamin K refers to structurally similar, fat-soluble vitamer Vitamins A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient which an organism ...
, as well as the
ubiquinone Coenzyme Q, also known as ubiquinone, is a coenzyme A cofactor is a non-protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallog ...

ubiquinone
s, are examples of this class. Prokaryotes synthesize polyprenols (called s) in which the terminal isoprenoid unit attached to oxygen remains unsaturated, whereas in animal polyprenols (
dolichol Dolichol refers to any of a group of long-chain mostly unsaturated organic compounds that are made up of varying numbers of isoprene units terminating in an α-saturated isoprenoid group, containing an alcohol File:Alcohol general.svg, uprigh ...

dolichol
s) the terminal isoprenoid is reduced.


Saccharolipids

Saccharolipid Saccharolipids are chemical compounds A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having ...
s describe compounds in which fatty acids are linked to a sugar backbone, forming structures that are compatible with membrane bilayers. In the saccharolipids, a
monosaccharide Monosaccharides (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ap ...
substitutes for the glycerol backbone present in glycerolipids and glycerophospholipids. The most familiar saccharolipids are the acylated
glucosamine Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylation, glycosylated proteins and lipids. Glucosamine is part of the structure of two polysaccharides, chitosan and chitin. Glucosamine is o ...

glucosamine
precursors of the component of the
lipopolysaccharide Lipopolysaccharides (LPS) are large molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change ...

lipopolysaccharide
s in
Gram-negative bacteria Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), do ...
. Typical lipid A molecules are
disaccharides A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular sugar, refers to suc ...
of glucosamine, which are derivatized with as many as seven fatty-acyl chains. The minimal lipopolysaccharide required for growth in is Kdo2-Lipid A, a hexa-acylated disaccharide of glucosamine that is glycosylated with two 3-deoxy-D-manno-octulosonic acid (Kdo) residues.


Polyketides

Polyketides are synthesized by polymerization of
acetyl In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . ...

acetyl
and subunits by classic enzymes as well as iterative and multimodular enzymes that share mechanistic features with the
fatty acid synthase Fatty acid synthase (FAS) is an enzyme that in humans is encoded by the ''FASN'' gene. Fatty acid synthase is a multi-enzyme protein that catalyzes fatty acid synthesis. It is not a single enzyme but a whole enzymatic system composed of two identi ...

fatty acid synthase
s. They comprise many
secondary metabolite Secondary metabolites, also called specialised metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a classical language bel ...
s and
natural products A natural product is a or produced by a living organism—that is, found in . In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by (both and ) and have played a central role ...
from animal, plant, bacterial, fungal and marine sources, and have great structural diversity. Many
polyketidePolyketides are a large group of secondary metabolites which either contain alternating carbonyl groups and methylene groups (-CO-CH2-), or are derived from precursors which contain such alternating groups. Many polyketides are medicinal or exhibit a ...
s are cyclic molecules whose backbones are often further modified by
glycosylation Glycosylation (see also chemical glycosylationA chemical glycosylation reaction involves the coupling of a glycosyl donor, to a glycosyl acceptor forming a glycoside. If both the donor and acceptor are sugars, then the product is an oligosacchar ...

glycosylation
,
methylation In the chemical sciences, methylation denotes the addition of a methyl group A methyl group is an alkyl derived from methane, containing one carbon atom chemical bond, bonded to three hydrogen atoms — CH3. In chemical formula, fo ...

methylation
,
hydroxylation In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...
,
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
, or other processes. Many commonly used anti-microbial, anti-parasitic, and
anti-cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biol ...
agents are polyketides or polyketide derivatives, such as
erythromycin Erythromycin is an antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () i ...

erythromycin
s,
tetracyclines Tetracyclines are a group of broad-spectrum antibiotic compounds that have a common basic structure and are either isolated directly from several species of ''Streptomyces'' bacteria or produced semi-synthetically from those isolated compounds. Tet ...
,
avermectin 300px, Ivermectin, one of the avermectins The avermectins are a series of drugs and pesticides used to treat parasitic worms and insect Pest (organism), pests. They are a group of 16-membered macrocyclic lactone derivatives with potent anthelmintic ...
s, and antitumor
epothilone The epothilones are a class of potential cancer drugs. Like taxanes, they prevent cancer cells from dividing by interfering with tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular protein 300px ...

epothilone
s.


Biological functions


Component of biological membranes

Eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

Eukaryotic
cells feature the compartmentalized membrane-bound
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
s that carry out different biological functions. The
glycerophospholipids Glycerophospholipids or phosphoglycerides are glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and ...

glycerophospholipids
are the main structural component of
biological membranes A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates Cell (biology), cell from the extracellular, external environment or creates intracellular compartments. Biological membranes, in the form of e ...
, as the cellular
plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...
and the intracellular membranes of
organelle In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
s; in animal cells, the plasma membrane physically separates the
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chem ...
components from the
extracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chem ...
environment. The glycerophospholipids are
amphipathic 250px, Cross-section view of the structures that can be formed by phospholipids, biological amphiphiles in aqueous solutions. Unlike this illustration, micelles are usually formed by non-biological, single-chain, amphiphiles, soaps or detergents, ...
molecules (containing both
hydrophobic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence ...
and
hydrophilic A hydrophile is a molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In phys ...
regions) that contain a glycerol core linked to two fatty acid-derived "tails" by
ester An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

ester
linkages and to one "head" group by a
phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

phosphate
ester linkage. While glycerophospholipids are the major component of biological membranes, other non-glyceride lipid components such as
sphingomyelin Sphingomyelin (SPH, ˌsfɪŋɡoˈmaɪəlɪn) is a type of sphingolipid Sphingolipids are a class of lipids containing a backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extrac ...

sphingomyelin
and
sterol Sterol is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and synth ...

sterol
s (mainly
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
in animal cell membranes) are also found in biological membranes. In plants and algae, the galactosyldiacylglycerols,Heinz E. (1996). "Plant glycolipids: structure, isolation and analysis", pp. 211–332 in ''Advances in Lipid Methodology'', Vol. 3. W.W. Christie (ed.). Oily Press, Dundee. and sulfoquinovosyldiacylglycerol, which lack a phosphate group, are important components of membranes of chloroplasts and related organelles and are the most abundant lipids in photosynthetic tissues, including those of higher plants, algae and certain bacteria. Plant thylakoid membranes have the largest lipid component of a non-bilayer forming monogalactosyl diglyceride (MGDG), and little phospholipids; despite this unique lipid composition, chloroplast thylakoid membranes have been shown to contain a dynamic lipid-bilayer matrix as revealed by magnetic resonance and electron microscope studies. A biological membrane is a form of
lamellar phase Lamellar phase refers generally to packing of polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis ...
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electrical charge on one side and a negative charge on another side, which produces the resting pot ...
. The formation of lipid bilayers is an energetically preferred process when the
glycerophospholipids Glycerophospholipids or phosphoglycerides are glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and ...

glycerophospholipids
described above are in an aqueous environment. This is known as the hydrophobic effect. In an aqueous system, the polar heads of lipids align towards the polar, aqueous environment, while the hydrophobic tails minimize their contact with water and tend to cluster together, forming a
vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and liv ...
; depending on the
concentration In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in t ...
of the lipid, this biophysical interaction may result in the formation of
micelle A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant phospholipid molecules dispersed in a liquid, forming a colloid, colloidal suspension (also known as associated co ...

micelle
s,
liposomes A liposome is a spherical vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) s in an aqueous An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water s ...
, or
lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane A polarized membrane is a lipid bilayer, lipid membrane that has a positive electrical charge on one side and a negative charge on another side, which produces the resting pot ...
s. Other aggregations are also observed and form part of the polymorphism of
amphiphile An amphiphile (a.k.a. amphipath; from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
(lipid) behavior. Phase behavior is an area of study within
biophysics Biophysics is an interdisciplinary science that applies approaches and methods traditionally used in physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), mot ...
and is the subject of current academic research. Micelles and bilayers form in the polar medium by a process known as the
hydrophobic effect The hydrophobic effect is the observed tendency of nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make u ...
. When dissolving a lipophilic or amphiphilic substance in a polar environment, the polar molecules (i.e., water in an aqueous solution) become more ordered around the dissolved lipophilic substance, since the polar molecules cannot form
hydrogen bond A hydrogen bond (or H-bond) is a primarily electrostatic Electrostatics is a branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department ...

hydrogen bond
s to the lipophilic areas of the
amphiphile An amphiphile (a.k.a. amphipath; from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
. So in an aqueous environment, the water molecules form an ordered "
clathrate A clathrate is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched a ...
" cage around the dissolved lipophilic molecule. The formation of lipids into
protocell A protocell (or protobiont) is a self-organized, endogenously ordered, spherical collection of lipids In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioch ...

protocell
membranes represents a key step in models of
abiogenesis In evolutionary biology Evolutionary biology is the subfield of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molec ...
, the origin of life.


Energy storage

Triglycerides, stored in adipose tissue, are a major form of energy storage both in animals and plants. They are a major 'source' of energy in aerobic respiration because they release the
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...
of twice more
dioxygen There are several known allotropy, allotropes of oxygen. The most familiar is oxygen, molecular oxygen (O2), present at significant levels in Atmosphere of Earth, Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the high ...
than carbohydrates such as glycogen do, per mass; this is due to the relatively low oxygen content of triglycerides. The complete oxidation of fatty acids releases about 38 kJ/g (9  kcal/g), compared with only 17 kJ/g (4 kcal/g) for the oxidative breakdown of
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s and
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
s. The
adipocyte Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the many basic types of animal An ...

adipocyte
, or fat cell, is designed for continuous synthesis and breakdown of triglycerides in animals, with breakdown controlled mainly by the activation of hormone-sensitive enzyme
lipase A lipase (, ) is any enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enz ...
. Migratory birds that must fly long distances without eating use triglycerides to fuel their flights.


Signaling

Evidence has emerged showing that
lipid signaling Lipid signaling, broadly defined, refers to any biological signaling In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal process ...
is a vital part of the
cell signaling In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
. Lipid signaling may occur via activation of
G protein-coupled G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily-related pro ...
or
nuclear receptor In the field of molecular biology, nuclear receptors are a class of proteins found within cells that are responsible for sensing Steroid hormone, steroid and Thyroid hormone, thyroid hormones and certain other molecules. In response, these recep ...
s, and members of several different lipid categories have been identified as signaling molecules and cellular messengers. These include
sphingosine-1-phosphate Sphingosine-1-phosphate (S1P) is a signaling In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image pro ...

sphingosine-1-phosphate
, a sphingolipid derived from ceramide that is a potent messenger molecule involved in regulating calcium mobilization, cell growth, and apoptosis;
diacylglycerol A diglyceride, or diacylglycerol (DAG), is a glyceride , the simplest possible fat after Triformin Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic. Glycer ...
(DAG) and the
phosphatidylinositol Phosphatidylinositol (or Inositol Phospholipid) consists of a family of lipids as illustrated on the right, where red is x, blue is y, and black is z, in the context of independent variation, a class of the Glycerophospholipid, phosphatidylglyceri ...

phosphatidylinositol
phosphates (PIPs), involved in calcium-mediated activation of
protein kinase C In cell biology, Protein kinase C, commonly abbreviated to PKC (EC 2.7.11.13), is a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and th ...
; the
prostaglandins The prostaglandins (PG) are a group of physiologically active lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Mole ...
, which are one type of fatty-acid derived eicosanoid involved in
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
and
immunity Immunity may refer to: Medicine * Immunity (medical), resistance of an organism to infection or disease * Immunity (journal), ''Immunity'' (journal), a scientific journal published by Cell Press Biology * Immune system Engineering * Radiofrequ ...
; the steroid hormones such as
estrogen Estrogens or oestrogens, are a class of natural or synthetic sex hormone Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormone A steroid hormone is a steroid that acts as a hormone. Steroid ho ...

estrogen
,
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and
cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland. ...

cortisol
, which modulate a host of functions such as reproduction, metabolism and blood pressure; and the
oxysterolAn oxysterol is a derivative of cholesterol Cholesterol (from the Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It i ...
s such as 25-hydroxy-cholesterol that are
liver X receptor The liver X receptor (LXR) is a member of the nuclear receptor In the field of molecular biology, nuclear receptors are a class of proteins found within cells that are responsible for sensing Steroid hormone, steroid and Thyroid hormone, thyro ...
agonist An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist ...

agonist
s. Phosphatidylserine lipids are known to be involved in signaling for the phagocytosis of apoptotic cells or pieces of cells. They accomplish this by being exposed to the extracellular face of the cell membrane after the inactivation of
flippase Flippases (rarely spelled flipases) are transmembrane lipid transporter protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a va ...

flippase
s which place them exclusively on the cytosolic side and the activation of scramblases, which scramble the orientation of the phospholipids. After this occurs, other cells recognize the phosphatidylserines and phagocytosize the cells or cell fragments exposing them.


Other functions

The "fat-soluble" vitamins (, D, E and ) – which are isoprene-based lipids – are essential nutrients stored in the liver and fatty tissues, with a diverse range of functions. Acyl-carnitines are involved in the transport and metabolism of fatty acids in and out of mitochondria, where they undergo
beta oxidation In biochemistry Biochemistry or biological chemistry, is the study of chemical process In a scientific Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable ...
. Polyprenols and their phosphorylated derivatives also play important transport roles, in this case the transport of
oligosaccharide An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sug ...
s across membranes. Polyprenol phosphate sugars and polyprenol diphosphate sugars function in extra-cytoplasmic glycosylation reactions, in extracellular polysaccharide biosynthesis (for instance,
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidia ...

peptidoglycan
polymerization in bacteria), and in eukaryotic protein N-
glycosylation Glycosylation (see also chemical glycosylationA chemical glycosylation reaction involves the coupling of a glycosyl donor, to a glycosyl acceptor forming a glycoside. If both the donor and acceptor are sugars, then the product is an oligosacchar ...

glycosylation
.
Cardiolipin Cardiolipin (IUPAC name 1,3-bis(''sn''-3’-phosphatidyl)-''sn''-glycerol) is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid composition. It can also be found in the membranes of most ...

Cardiolipin
s are a subclass of glycerophospholipids containing four acyl chains and three glycerol groups that are particularly abundant in the inner mitochondrial membrane. They are believed to activate enzymes involved with
oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), c ...

oxidative phosphorylation
. Lipids also form the basis of steroid hormones.


Metabolism

The major dietary lipids for humans and other animals are animal and plant triglycerides, sterols, and membrane phospholipids. The process of lipid metabolism synthesizes and degrades the lipid stores and produces the structural and functional lipids characteristic of individual tissues.


Biosynthesis

In animals, when there is an oversupply of dietary carbohydrate, the excess carbohydrate is converted to triglycerides. This involves the synthesis of fatty acids from
acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reaction Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organism In biology, an organism (from ...

acetyl-CoA
and the
esterification An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

esterification
of fatty acids in the production of triglycerides, a process called
lipogenesis Lipogenesis is the metabolic process through which acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl ...
. Fatty acids are made by
fatty acid synthase Fatty acid synthase (FAS) is an enzyme that in humans is encoded by the ''FASN'' gene. Fatty acid synthase is a multi-enzyme protein that catalyzes fatty acid synthesis. It is not a single enzyme but a whole enzymatic system composed of two identi ...

fatty acid synthase
s that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acetyl group, reduce it to an alcohol,
dehydrate In physiology, dehydration is a lack of total body water, with an accompanying disruption of Metabolism, metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temper ...
it to an
alkene In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo dur ...

alkene
group and then reduce it again to an
alkane In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, pr ...
group. The enzymes of fatty acid biosynthesis are divided into two groups, in animals and fungi all these fatty acid synthase reactions are carried out by a single multifunctional protein, while in plant
plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ' ...
s and bacteria separate enzymes perform each step in the pathway. The fatty acids may be subsequently converted to triglycerides that are packaged in
lipoproteins A lipoprotein is a assembly whose primary function is to transport (also known as ) molecules in water, as in or other s. They consist of a and center, surrounded by a outer shell, with the portions oriented outward toward the surrounding ...

lipoproteins
and secreted from the liver. The synthesis of
unsaturated fatty acid In nutrition Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It includes ingestion, Absorption (biology), absorption, Assimilation (biology), assimilation, biosynthesis, catab ...
s involves a
desaturation Desaturation may refer to: * In pulse oximetry, the condition of a low blood oxygen concentration * Reduction of colorfulness in image processing * Conversion of a saturated compound into an unsaturated compound by a removal of two hydrogen molecule ...
reaction, whereby a double bond is introduced into the fatty acyl chain. For example, in humans, the desaturation of
stearic acid Stearic acid ( , ) is a saturated fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properti ...

stearic acid
by
stearoyl-CoA desaturase-1 Stearoyl-CoA desaturase (Δ-9-desaturase) is an endoplasmic reticulum enzyme that catalyzes the rate-limiting step in the formation of Monounsaturated fat, monounsaturated fatty acids (MUFAs), specifically Oleic acid, oleate and Palmitoleic acid, p ...

stearoyl-CoA desaturase-1
produces
oleic acid Oleic acid is a fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and t ...

oleic acid
. The doubly unsaturated fatty acid
linoleic acid Linoleic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beha ...

linoleic acid
as well as the triply unsaturated
α-linolenic acid α-Linolenic acid (ALA), (from Greek language, Greek ''linon'', meaning flax), is an omega-3 fatty acid, ''n''−3, or omega-3, essential fatty acid. ALA is found in many seeds and oils, including flaxseed, walnuts, chia seed, chia, hemp, and m ...

α-linolenic acid
cannot be synthesized in mammalian tissues, and are therefore
essential fatty acid Essential fatty acids, or EFAs, are fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, proper ...
s and must be obtained from the diet. Triglyceride synthesis takes place in the
endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerol-3-phosphate and diacylglycerol.
Terpene Terpenes () are a class of natural product A natural product is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than ...
s and
isoprenoids The terpenoids, also known as isoprenoids, are a large and diverse class of naturally occurring organic chemicals , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain ca ...
, including the
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
s, are made by the assembly and modification of
isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals (including humans) and i ...

isoprene
units donated from the reactive precursors
isopentenyl pyrophosphate Isopentenyl pyrophosphate (IPP, isopentenyl diphosphate, or IDP) is an isoprenoid precursor. IPP is an intermediate in the classical, HMG-CoA reductase pathway (commonly called the mevalonate pathway) and in the ''non-mevalonate'' MEP pathway of i ...

isopentenyl pyrophosphate
and
dimethylallyl pyrophosphate Dimethylallyl pyrophosphate (DMAPP; or alternatively, dimethylallyl diphosphate (DMADP); also isoprenyl pyrophosphate) is an isoprenoid precursor. It is a product of both the mevalonate pathway and the MEP pathway of isoprenoid precursor biosynth ...
. These precursors can be made in different ways. In animals and
archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

archaea
, the
mevalonate pathway The mevalonate pathway, also known as the isoprenoid pathway or HMG-CoA reductase HMG-CoA reductase (3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, official symbol HMGCR) is the rate-controlling enzyme Enzymes () are proteins that act ...

mevalonate pathway
produces these compounds from acetyl-CoA, while in plants and bacteria the
non-mevalonate pathway The non-mevalonate pathway—also appearing as the mevalonate-independent pathway and the 2-''C''-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate (MEP/DOXP) pathway—is an alternative metabolic pathway for the biosynthesis Biosynthes ...

non-mevalonate pathway
uses pyruvate and
glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is the metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical ...

glyceraldehyde 3-phosphate
as substrates. One important reaction that uses these activated isoprene donors is steroid biosynthesis. Here, the isoprene units are joined together to make
squalene Squalene is an organic compound. With the formula (C5H8)6, it is a triterpene. It is a colourless oil although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as ''Squalus'' is a genus of sharks). Al ...

squalene
and then folded up and formed into a set of rings to make
lanosterol Lanosterol is a tetracyclic triterpenoid Triterpenes are a class of chemical compounds composed of three terpene units with the molecular formula C30H48; they may also be thought of as consisting of six isoprene units. Animals, plants and fungi a ...

lanosterol
. Lanosterol can then be converted into other steroids such as
cholesterol Cholesterol is any of a class of certain organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has co ...

cholesterol
and
ergosterol Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol Sterol is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: t ...

ergosterol
.


Degradation

Beta oxidation In biochemistry Biochemistry or biological chemistry, is the study of chemical process In a scientific Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable ...
is the metabolic process by which fatty acids are broken down in the
mitochondria A mitochondrion (; ) is a double-membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes ...

mitochondria
or in
peroxisomes A peroxisome () is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are pa ...
to generate
acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reaction Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organism In biology, an organism (from ...

acetyl-CoA
. For the most part, fatty acids are oxidized by a mechanism that is similar to, but not identical with, a reversal of the process of fatty acid synthesis. That is, two-carbon fragments are removed sequentially from the carboxyl end of the acid after steps of
dehydrogenation Dehydrogenation is the a chemical reaction that involves the removal of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and p ...
, hydration, and
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
to form a beta-keto acid, which is split by
thiolysis Thiolysis is a reaction with a thiol A thiol () or thiol derivative is any organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known a ...
. The acetyl-CoA is then ultimately converted into
ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armenia Tree Project * Association for Transpersonal Psychology * ATP architects engineers office * ATP ...

ATP
, CO2, and H2O using the
citric acid cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reactions to release stored energy through the redox, oxidation of acetyl-CoA derived from carbohydra ...

citric acid cycle
and the
electron transport chain An electron transport chain (ETC) is a series of protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chain Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Anc ...

electron transport chain
. Hence the citric acid cycle can start at acetyl-CoA when fat is being broken down for energy if there is little or no glucose available. The energy yield of the complete oxidation of the fatty acid palmitate is 106 ATP. Unsaturated and odd-chain fatty acids require additional enzymatic steps for degradation.


Nutrition and health

Most of the fat found in food is in the form of triglycerides, cholesterol, and phospholipids. Some dietary fat is necessary to facilitate absorption of fat-soluble vitamins (, D, E, and ) and
carotenoids Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
. Humans and other mammals have a dietary requirement for certain essential fatty acids, such as
linoleic acid Linoleic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beha ...

linoleic acid
(an
omega-6 fatty acid Omega-6 fatty acids (also referred to as ω-6 fatty acids or ''n''-6 fatty acids) are a family of polyunsaturated fatty acidsPolyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This ...
) and
alpha-linolenic acid α-Linolenic acid (ALA), (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popul ...

alpha-linolenic acid
(an omega-3 fatty acid) because they cannot be synthesized from simple precursors in the diet. Both of these fatty acids are 18-carbon
polyunsaturated fatty acidsPolyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oil A drying oil is an oil that ...
differing in the number and position of the double bonds. Most
vegetable oil Vegetable oils, or vegetable fats, are oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, eleme ...
s are rich in linoleic acid (
safflower Safflower, ''Carthamus tinctorius'', is a highly branched, herbaceous, thistle-like annual plant 240px, Peas are an annual plant. An annual plant is a plant that completes its biological life cycle, life cycle, from germination to the produ ...

safflower
,
sunflower ''Helianthus'' () is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), ...

sunflower
, and
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American English, North American and Australian English), is a cereal grain first domesticated by indigenous peoples of the Americas, indige ...

corn
oils). Alpha-linolenic acid is found in the green leaves of plants and in some seeds, nuts, and legumes (in particular
flax Flax, also known as common flax or linseed, is a flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may ...
,
rapeseed Rapeseed (''Brassica napus ''subsp.'' napus''), also known as rape, or oilseed rape, is a bright-yellow flowering member of the family Brassicaceae Brassicaceae () or Cruciferae () is a medium-sized and economically important family ...

rapeseed
,
walnut A walnut is the Nut (fruit), nut of any tree of the genus ''Juglans'' (family Juglandaceae), particularly the Persian or English walnut, ''Juglans regia''. A walnut is the edible seed of a drupe, and thus not a true botanical nut. It is com ...

walnut
, and
soy The soybean or soya bean (''Glycine max'') is a species of legume native to East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, ...
).
Fish oil Fish oil is oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to ...
s are particularly rich in the longer-chain omega-3 fatty acids
eicosapentaenoic acid Eicosapentaenoic acid (EPA; also icosapentaenoic acid) is an omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) ...
(EPA) and
docosahexaenoic acid Docosahexaenoic acid (DHA) is an omega-3 fatty acid Omega−3 fatty acids, also called Omega-3 oils, ω−3 fatty acids or ''n''−3 fatty acids, are polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that con ...

docosahexaenoic acid
(DHA). Many studies have shown positive health benefits associated with consumption of omega-3 fatty acids on infant development, cancer, cardiovascular diseases, and various mental illnesses (such as depression, attention-deficit hyperactivity disorder, and dementia). In contrast, it is now well-established that consumption of
trans fat Trans fat, also called trans-unsaturated fatty acids or trans fatty acids, is a type of unsaturated fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Anci ...
s, such as those present in partially hydrogenated vegetable oils, are a risk factor for
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped ...
. Fats that are good for one may be turned into trans fats by improper cooking methods that result in overcooking the lipids. A few studies have suggested that total dietary fat intake is linked to an increased risk of obesity and diabetes; however, a number of very large studies, including the Women's Health Initiative Dietary Modification Trial, an eight-year study of 49,000 women, the Nurses' Health Study, and the Health Professionals Follow-up Study, revealed no such links. None of these studies suggested any connection between percentage of calories from fat and risk of cancer, heart disease, or weight gain. The Nutrition Source, a website maintained by the department of nutrition at the T. H. Chan School of Public Health at
Harvard University Harvard University is a private Private or privates may refer to: Music * "In Private "In Private" was the third single in a row to be a charting success for United Kingdom, British singer Dusty Springfield, after an absence of nearly t ...

Harvard University
, summarizes the current evidence on the effect of dietary fat: "Detailed research—much of it done at Harvard—shows that the total amount of fat in the diet isn't really linked with weight or disease."


See also

* * * * * * * * * * , a class of natural products composed of long aliphatic chains and phenolic rings that occur in plants, fungi and bacteria


References


Bibliography

* * * *


External links

Introductory
List of lipid-related web sitesNature Lipidomics Gateway
– Round-up and summaries of recent lipid research
Lipid Library
– General reference on lipid chemistry and biochemistry
Cyberlipid.org
– Resources and history for lipids.

– Modeling of Lipid Membranes
Lipids, Membranes and Vesicle Trafficking
– The Virtual Library of Biochemistry, Molecular Biology and Cell Biology Nomenclature
IUPAC nomenclature of lipids
Databases

– Comprehensive lipid and lipid-associated gene/protein databases.
LipidBank
– Japanese database of lipids and related properties, spectral data and references. General
ApolloLipids
– Provides dyslipidemia and cardiovascular disease prevention and treatment information as well as continuing medical education programs
National Lipid Association
– Professional medical education organization for health care professionals who seek to prevent morbidity and mortality stemming from dyslipidemias and other cholesterol-related disorders. {{Portal bar, Food, Biology * Underwater diving physiology