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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 Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous syst ...
s in protein, carbohydrate and lipid
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
. Its main function is to deliver the
acetyl In organic chemistry Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds, which contain carbon in covalent bonding.Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemis ...

acetyl
group to 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
(Krebs cycle) to be
oxidized (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A ...

oxidized
for energy production.
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 aci ...
(CoASH or CoA) consists of a β-mercaptoethylamine group linked to the vitamin
pantothenic acid Pantothenic acid, also called vitamin B5 is a water-soluble B vitamin and therefore an essential nutrient. All animals require pantothenic acid in order to synthesize coenzyme A (CoA) – essential for fatty acid metabolism – as well as to ...

pantothenic acid
(B5) through an
amide linkage A peptide bond is an amide type of Covalent bond, covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein chain. It can ...
and 3'-phosphorylated ADP. The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked to the
sulfhydryl A thiol () or thiol derivative is any organosulfur compound Organosulfur compounds are organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, eleme ...
substituent of the β-mercaptoethylamine group. This
thioester In chemistry thioesters are compounds with the 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 functi ...

thioester
linkage is a "high energy" bond, which is particularly reactive.
Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

Hydrolysis
of the thioester bond is
exergonic An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic In chemical thermodynamics Chemical thermodynamics is the study of the interrelation of heat ...

exergonic
(−31.5 kJ/mol). CoA is acetylated to acetyl-CoA by the breakdown of
carbohydrates is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galacto ...
through
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
and by the breakdown of
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 ...
through β-oxidation. Acetyl-CoA then enters the citric acid cycle, where the acetyl group is oxidized to carbon dioxide and water, and the energy released is captured in the form of 11
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
and one GTP per acetyl group.
Konrad Bloch Konrad Emil Bloch (), Fellow of the Royal Society, ForMemRS (21 January 1912 – 15 October 2000) was a German American biochemist. Bloch received the Nobel Prize in Physiology or Medicine in 1964 (joint with Feodor Lynen) for discoveries concernin ...

Konrad Bloch
and
Feodor Lynen Feodor Felix Konrad Lynen (; 6 April 19116 August 1979) was a Germany, German biochemist. In 1964 he won the Nobel Prize in Physiology or Medicine together with Konrad Emil Bloch, Konrad Bloch for their discoveries concerning the mechanism and re ...
were awarded the 1964
Nobel Prize in Physiology and Medicine ) , name = The Nobel Prize in Physiology or Medicine , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL" ...
for their discoveries linking acetyl-CoA and fatty acid metabolism.
Fritz Lipmann Fritz Albert Lipmann (June 12, 1899 – July 24, 1986) was a German-American biochemist Biochemists are scientists who are trained in biochemistry Biochemistry or biological chemistry, is the study of chemical processes within and relating t ...

Fritz Lipmann
won the Nobel Prize in 1953 for his discovery of the cofactor
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 aci ...
.


Direct synthesis

The acetylation of CoA is determined by the carbon sources.


Extramitochondrial

* At high
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
levels,
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
takes place rapidly, thus increasing the amount of
citrate Citric 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, behav ...
produced from the tricarboxylic acid cycle. This citrate is then exported to other
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 outside the mitochondria to be broken into acetyl-CoA and
oxaloacetate Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemi ...

oxaloacetate
by the
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 enzyme converts the substrates in ...

enzyme
ATP citrate lyase ATP citrate synthase (also ATP citrate lyase (ACLY)) is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate ...
(ACL). This principal reaction is coupled with the hydrolysis of ATP. * At low glucose levels: ** CoA is acetylated using
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetal image:Simple Periodic Table Chart-en.svg, upright=1.75, Nonmetals (and metalloids) in the periodic table: Metalloids are i ...

acetate
by
acetyl-CoA synthetase Acetyl-CoA synthetase (ACS) or Acetate-CoA ligase is an enzyme () involved in metabolism of acetate. It is in the ligase class of enzymes, meaning that it catalyzes the formation of a new chemical bond between two large molecules. Reaction The tw ...
(ACS), also coupled with
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
hydrolysis. **
Ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

Ethanol
also serves as a carbon source for acetylation of CoA utilizing the enzyme
alcohol dehydrogenase Alcohol dehydrogenases (ADH) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to NADH. ...

alcohol dehydrogenase
. ** Degradation of branched-chain
ketogenic 300px, Ketogenesis pathway. The three ketone bodies (acetoacetate, acetone, and beta-hydroxy-butyrate) are marked within orange boxes Ketogenesis is the biochemical Biochemistry or biological chemistry, is the study of chemical processes withi ...
amino acid Amino acids are 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, a ...

amino acid
s such as
valine Valine (symbol Val or V) 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, bo ...

valine
,
leucine Leucine (symbol Leu or L) is an essential amino acid An essential amino acid, or indispensable amino acid, is an amino acid Amino acids are organic compounds that contain amino (–NH2) and Carboxylic acid, carboxyl (–COOH) functional gro ...

leucine
, and
isoleucine Isoleucine (symbol Ile or I) 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 bon ...

isoleucine
occurs. These amino acids are converted to α-ketoacids by
transamination Transamination, a chemical reaction that transfers an amino group In organic chemistry, amines (, ) are organic compound, compounds and functional groups that contain a base (chemistry), basic nitrogen atom with a lone pair. Amines are form ...

transamination
and eventually to isovaleryl-CoA through oxidative decarboxylation by an α-ketoacid dehydrogenase complex. Isovaleryl-CoA undergoes
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. With a standard atomic weight of , hydrogen is the lightest elem ...
,
carboxylationCarboxylation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant chem ...
and hydration to form another CoA-derivative intermediate before it is cleaved into acetyl-CoA and
acetoacetate Acetoacetic acid (also acetoacetate and diacetic acid) is the organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound ...
.


Intramitochondrial

* At high glucose levels, acetyl-CoA is produced through
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
.
Pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, 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 ...

Pyruvate
undergoes oxidative decarboxylation in which it loses its
carboxyl A carboxylic acid is an organic acid An organic 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: th ...

carboxyl
group (as
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
) to form acetyl-CoA, giving off 33.5 kJ/mol of energy. The oxidative conversion of pyruvate into acetyl-CoA is referred to as the pyruvate dehydrogenase reaction. It is catalyzed by the
pyruvate dehydrogenase complex Pyruvate dehydrogenase complex (PDC) is a complex of three enzymes that converts pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Acetyl-CoA may then be used in the citric acid cycle to carry out cellular respiration, and this ...
. Other conversions between pyruvate and acetyl-CoA are possible. For example,
pyruvate formate lyase In enzymology 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 enzyme converts the ...
disproportionates pyruvate into acetyl-CoA and
formic acid Formic acid, systematically named methanoic acid, is the simplest carboxylic acid A carboxylic acid is an organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acid ...

formic acid
. * At low glucose levels, the production of acetyl-CoA is linked to β-oxidation of
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. Fatty acids are first converted to acyl-CoA. Acyl-CoA is then degraded in a four-step cycle of oxidation, hydration, oxidation and
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 ...
catalyzed by four respective enzymes, namely
acyl-CoA dehydrogenaseAcyl-CoA dehydrogenases (ACADs) are a class of enzymes that function to catalyze the initial step in each cycle of fatty acid β-oxidation in the mitochondria A mitochondrion (, plural mitochondria) is a double membrane-bound organelle found ...
,
enoyl-CoA hydratase Enoyl-CoA hydratase (ECH) or crotonase is an 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), su ...
, 3-hydroxyacyl-CoA dehydrogenase, and
thiolase Thiolases, also known as acetyl-coenzyme A acetyltransferases (ACAT), are enzymes which convert two units of acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and ...
. The cycle produces a new fatty acid chain with two fewer carbons and acetyl-CoA as a byproduct.


Functions


Intermediates in various pathways

* In Cellular Respiration *
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
: ** Through a series of chemical reactions, stored energy is released through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into
adenosine triphosphate Adenosine triphosphate (ATP) 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 properti ...

adenosine triphosphate
(ATP) and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
. *
Fatty acid metabolism Fatty acid metabolism consists of various metabolic processes involving or closely related to fatty acids, a family of molecules classified within the lipid macronutrient category. These processes can mainly be divided into catabolic processes t ...

Fatty acid metabolism
** Acetyl-CoA is produced by the breakdown of both
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 (by
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
) and
lipids 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 mechanis ...

lipids
(by β-oxidation). It then enters the citric acid cycle in the mitochondrion by combining with
oxaloacetate Oxaloacetic acid (also known as oxalacetic acid or OAA) is a crystalline organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemi ...

oxaloacetate
to form
citrate Citric 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, behav ...

citrate
. ** Two acetyl-CoA molecules condense to form
acetoacetyl-CoA Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathwayImage:Wiki pathway hi def tiff.tif, 500px, Mevalonate pathway diagram showing the conversion of acetyl-CoA into isopentenyl pyrophosphate, the essential building block of all isop ...

acetoacetyl-CoA
, which gives rise to the formation of
acetoacetate Acetoacetic acid (also acetoacetate and diacetic acid) is the organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound ...

acetoacetate
and β-hydroxybutyrate. Acetoacetate, β-hydroxybutyrate, and their spontaneous breakdown product
acetone Acetone, or propanone, is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, ...

acetone
are frequently, but confusingly, known as
ketone bodies Ketone bodies are water-soluble In chemistry, solubility is ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inabi ...

ketone bodies
(as they are not "bodies" at all, but water-soluble chemical substances). The ketone bodies are released by the
liver The liver is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's t ...

liver
into the blood. All cells with mitochondria can take ketone bodies up from the blood and reconvert them into acetyl-CoA, which can then be used as fuel in their citric acid cycles, as no other tissue can divert its oxaloacetate into the in the way that the liver does. Unlike free fatty acids, ketone bodies can cross the blood-brain barrier and are therefore available as fuel for the cells of the
central nervous system The central nervous system (CNS) is the part of the nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
, acting as a substitute for glucose, on which these cells normally survive. The occurrence of high levels of ketone bodies in the blood during
starvation Starvation is a severe deficiency in caloric 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 t ...

starvation
, a
low-carbohydrate diet Low-carbohydrate diets restrict carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consis ...
, prolonged heavy exercise, and uncontrolled type-1 diabetes mellitus is known as
ketosis Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the blood or urine. Physiologic ketosis is a normal response to low glucose availability, such as low-carbohydrate diets or fasting, that provides an additional ene ...
, and in its extreme form in out-of-control type-1 diabetes mellitus, as
ketoacidosis Ketoacidosis is a metabolic state caused by uncontrolled production of ketone bodies that cause a metabolic acidosis. While ketosis refers to any elevation of blood Ketone bodies, ketones, ketoacidosis is a specific pathologic condition that results ...
. ** On the other hand, when the
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets; it is considered to be the main Anabolism, anabolic hormone of the body. It regulates the metabolism of carbohydrates, fats and p ...

insulin
concentration in the blood is high, and that of
glucagon Glucagon is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine ...

glucagon
is low (i.e. after meals), the acetyl-CoA produced by glycolysis condenses as normal with oxaloacetate to form citrate in the mitochondrion. However, instead of continuing through the citric acid cycle to be converted to carbon dioxide and water, the citrate is removed from the mitochondrion into the
cytoplasm 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 ...
. There it is cleaved by
ATP citrate lyase ATP citrate synthase (also ATP citrate lyase (ACLY)) is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate ...
into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to the mitochondrion as malate (and then converted back into oxaloacetate to transfer more acetyl-CoA out of the mitochondrion). This cytosolic acetyl-CoA can then be used to synthesize fatty acids through carboxylation by
acetyl-CoA carboxylase Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life i ...
into
malonyl CoA Malonyl-CoA is a coenzyme A derivative of malonic acid. Functions It plays a key role in chain elongation in fatty acid biosynthesis and polyketide biosynthesis. Fatty acid biosynthesis In the former, it provides 2-carbon units to fatty acids and ...

malonyl CoA
, the first committed step in the synthesis of fatty acids. This conversion occurs primarily in the liver,
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
and lactating
mammary gland A mammary gland is an exocrine gland Exocrine glands are gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormone A hormone (from the Greek participle , "setting in motion") is any m ...
s, where the fatty acids are combined with
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 ...
to form
triglyceride A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) 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 an ...

triglyceride
s, the major fuel reservoir of most animals. Fatty acids are also components of the
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 that make up the bulk 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 ...
s of all
cellular membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates the interior of all cells from the out ...
s. ** In plants, ''de novo'' fatty acid synthesis occurs in the
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. Many
seed A seed is an embryonic ''Embryonic'' is the twelfth studio album by experimental rock band the Flaming Lips released on October 13, 2009, on Warner Bros. Records, Warner Bros. The band's first double album, it was released to generally positi ...

seed
s accumulate large reservoirs of seed oils to support
germination Germination is the process by which an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biolog ...

germination
and early growth of the seedling before it is a net
photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthetic
organism. ** The
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a s ...
ic acetyl-CoA can also condense with
acetoacetyl-CoA Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathwayImage:Wiki pathway hi def tiff.tif, 500px, Mevalonate pathway diagram showing the conversion of acetyl-CoA into isopentenyl pyrophosphate, the essential building block of all isop ...

acetoacetyl-CoA
to form 3-hydroxy-3-methylglutaryl-CoA (
HMG-CoA β-Hydroxy β-methylglutaryl-CoA (HMG-CoA), also known as 3-hydroxy-3-methylglutaryl-CoA, is an intermediate in the mevalonate and ketogenesis pathways. It is formed from acetyl CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in ...
) which is the rate-limiting step controlling the .
Cholesterol Cholesterol is any of a class of certain organic compound, organic molecules. A cholesterol is a sterol (or chemical modification, modified steroid), a type of lipid. Cholesterol is biosynthesis, biosynthesized by all animal Cell (biology)#Euk ...

Cholesterol
can be used as is, as a structural component of cellular membranes, or it can be used to synthesize
steroid hormones A steroid hormone is a steroid , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of ...

steroid hormones
,
bile salts Bile acids are steroid , hypothetical a steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federatio ...
, and
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 ...
. ** Acetyl-CoA can be carboxylated in the cytosol by
acetyl-CoA carboxylase Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life i ...
, giving rise to
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
, a substrate required for synthesis of
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenol Polyphenols () are a large family of naturally occurring s characterized by multiples of units. They are abunda ...
s and related
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, for elongation of fatty acids to produce
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,
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homology (biology), homologous, differing in the ...
, and seed oils in members of the
Brassica ''Brassica'' () is a genus of plants in the cabbage and mustard Mustard may refer to: Food and plants * Mustard (condiment) Mustard is a condiment made from the seeds A seed is an Plant embryogenesis, embryonic plant enclosed in a te ...
family, and for of proteins and other phytochemicals. In plants, these include
sesquiterpene Sesquiterpenes are a class of terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plant ...
s,
brassinosteroid Brassinosteroids (BRs) are a class of polyhydroxysteroids that have been recognized as a sixth class of plant hormones Plant hormones (or phytohormones) are signal molecule In biology, cell signaling (cell signalling in British English), or ce ...
s (hormones), and membrane
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. *
Steroid synthesis , a steroid with 27 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC-approved ring lettering and atom numbering. A steroid is a biologically active organic compound with four rings arranged in a specifi ...

Steroid synthesis
: ** Acetyl-CoA participates in 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
by partaking in the synthesis of hydroxymethyl glutaryl-CoA. * Acetylcholine synthesis: ** Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter acetylcholine. Choline, in combination with acetyl-CoA, is catalyzed by the enzyme choline acetyltransferase to produce acetylcholine and
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 aci ...
as a byproduct. * Melatonin synthesis * Acetylation ** Acetyl-CoA is also the source of the acetyl group incorporated onto certain lysine residues of histone and nonhistone proteins in the posttranslational modification acetylation. This acetylation is catalyzed by acetyltransferases. This acetylation affects cell growth, mitosis, and apoptosis. *Allosteric regulator ** Acetyl-CoA serves as an allosteric regulation, allosteric regulator of pyruvate dehydrogenase kinase (PDK). It regulates through the ratio of acetyl-CoA versus CoA. Increased concentration of acetyl-CoA activates PDK. ** Acetyl-CoA is also an allosteric activator of pyruvate carboxylase.


Interactive pathway map

''Click on genes, proteins and metabolites below to visit Portal:Gene Wiki, Gene Wiki pages and related Wikipedia articles. The pathway can be downloaded and edited a
WikiPathways
''


See also

* Malonyl-CoA decarboxylase


References


External links

* {{DEFAULTSORT:Acetyl-Coa Cholinergics Metabolism Thioesters of coenzyme A