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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 approximately 10.7 million as of ...
'' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of
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 joined by a . Common examp ...

sugar
and the most basic units (
monomerA monomer ( ; '' mono-'', "one" + '' -mer'', "part") is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrical ...

monomer
s) of
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 consisting of carbon (C), hydrogen (H) and oxygen (O) ato ...
s. The general formula is , or ''n''(H2O)''n''or ''n'' albeit not all molecules fitting this formula (e.g.
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, ...

acetic acid
) are carbohydrates. They are usually colorless,
water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , even though it provide ...

water
-
soluble Solubility is the property of a solid, liquid or gaseous chemical substance called ''solution, solute'' to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance fundamentally depends on the Physical property, physical an ...
, and
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macrosco ...

crystal
line solids. Contrary to their name (sugars), only some monosaccharides have a
sweet taste
sweet taste
. Examples of monosaccharides include
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
(dextrose),
fructose Fructose, or fruit sugar, is a ketonic simple sugar Monosaccharides (from Greek language, Greek ''wikt:μόνος, monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar and the most basic units (monomers ...

fructose
(levulose), and
galactose Galactose (, '' galacto-'' + ''-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. ...
. Monosaccharides are the building blocks of
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-galactose and a molecule of ...
s (such as
sucrose Sucrose is a type of 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 sucrose, a disaccharide composed of glucose a ...

sucrose
and
lactose Lactose, 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-g ...

lactose
) and
polysaccharide , a beta-glucan is an example of a (1→4)-β-D-glucan composed of glucose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Gl ...
s (such as
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
and
starch Starch or amylum is a consisting of numerous units joined by s. This is produced by most green s for energy storage. Worldwide, it is the most common carbohydrate in human diets, and is contained in large amounts in s like , es, (corn), , ...
). Each
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atom that supports a
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group ...

hydroxyl
group is
chiral Chirality is a property of important in several branches of science. The word ''chirality'' is derived from the (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its ; that is, i ...
, except those at the end of the chain. This gives rise to a number of
isomer In , isomers are s or s with identical s — that is, same number of of each — but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Isomers do not necessarily share similar or . Two main forms of ...

isomer
ic forms, all with the same chemical formula. For instance, galactose and glucose are both
aldohexose 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, mo ...
s, but have different physical structures and chemical properties. The monosaccharide glucose plays a pivotal role in
metabolism 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 the energy in food to energy available to run cellu ...

metabolism
, where the chemical energy is extracted through
glycolysis Glycolysis is the metabolic pathway In biochemistry 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 ...

glycolysis
and 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 reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transfor ...

citric acid cycle
to provide energy to living organisms. Some other monosaccharides can be converted in the living organism to glucose.


Structure and nomenclature

With few exceptions (e.g.,
deoxyribose Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet ...

deoxyribose
), monosaccharides have this
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 parentheses, dashes, brackets, commas and ...
: (CH2O)''x'', where conventionally ''x'' ≥ 3. Monosaccharides can be classified by the number ''x'' of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atoms they contain:
triose is an aldotriose because the carbonyl group is at the end of the chain Image:Dihydroxyacetone.png">150px, Dihydroxyacetone is a ketone, ketotriose because the carbonyl group is the center of the chain. A triose is a monosaccharide, or simple sug ...
(3),
tetroseA tetrose is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many o ...

tetrose
(4),
pentoseIn chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atom, atoms. The chemical formula of all pentoses is , and their molecular weight is 150.13 g/mol.
(5),
hexose 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, mo ...
(6),
heptose A heptose is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many ...
(7), and so on. Glucose, used as an energy source and for the synthesis of starch, glycogen and cellulose, is a
hexose 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, mo ...
. Ribose and deoxyribose (in
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repe ...

RNA
and
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
respectively) are pentose sugars. Examples of heptoses include the
ketose A ketose is a monosaccharide containing one ketone In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, s ...

ketose
s,
mannoheptulose Mannoheptulose is a heptose, a monosaccharide with seven carbon atoms, and a ketose, with the characteristic carbonyl group of the carbohydrate present on a secondary carbon (functioning as a ketone group). The sugar alcohol form of mannoheptulose ...

mannoheptulose
and
sedoheptulose Sedoheptulose or D-''altro''-heptulose is a ketoheptose—a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Swe ...

sedoheptulose
. Monosaccharides with eight or more carbons are rarely observed as they are quite unstable. In
aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute an ...
s monosaccharides exist as rings if they have more than four carbons.


Linear-chain monosaccharides

Simple monosaccharides have a linear and unbranched carbon skeleton with one
carbonyl 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 Chemistr ...

carbonyl
(C=O)
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 ...
, and one
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group ...

hydroxyl
(OH) group on each of the remaining carbon
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 having volume. All everyday objects that can be touched are ultimately composed of atom ...

atom
s. Therefore, the molecular structure of a simple monosaccharide can be written as H(CHOH)''n''(C=O)(CHOH)''m''H, where ''n'' + 1 + ''m'' = ''x''; so that its elemental formula is C''x''H2''x''O''x''. By convention, the carbon atoms are numbered from 1 to ''x'' along the backbone, starting from the end that is closest to the C=O group. Monosaccharides are the simplest units of carbohydrates and the simplest form of sugar. If the carbonyl is at position 1 (that is, ''n'' or ''m'' is zero), the molecule begins with a formyl group H(C=O)− and is technically an
aldehyde Chemically, an aldehyde is a compound containing a 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 fu ...

aldehyde
. In that case, the compound is termed an
aldose An aldose is a monosaccharide (a simple sugar) with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and Hydroxy group, hydroxyl groups connected to all the other carbon atoms. Aldoses can be distingui ...

aldose
. Otherwise, the molecule has a
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
group, a carbonyl −(C=O)− between two carbons; then it is formally a
ketone In chemistry, a ketone is a functional group with the structure R2C=O, where R can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond). The simplest ketone is acetone (R = R' = methyl) ...
, and is termed a
ketose A ketose is a monosaccharide containing one ketone In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, s ...

ketose
. Ketoses of biological interest usually have the carbonyl at position 2. The various classifications above can be combined, resulting in names such as "aldohexose" and "ketotriose". A more general nomenclature for open-chain monosaccharides combines a Greek prefix to indicate the number of carbons (tri-, tetr-, pent-, hex-, etc.) with the suffixes "-ose" for aldoses and "-ulose" for ketoses. In the latter case, if the carbonyl is not at position 2, its position is then indicated by a numeric infix. So, for example, H(C=O)(CHOH)4H is pentose, H(CHOH)(C=O)(CHOH)3H is pentulose, and H(CHOH)2(C=O)(CHOH)2H is pent-3-ulose.


Open-chain stereoisomers

Two monosaccharides with equivalent
molecular graph In chemical graph theory and in mathematical chemistry, a molecular graph or chemical graph is a representation of the structural formula of a chemical compound in terms of graph theory. A chemical graph is a labeled graph whose vertices correspond ...
s (same chain length and same carbonyl position) may still be distinct
stereoisomer In stereochemistry s. Stereochemistry focuses on stereoisomer In stereochemistry, stereoisomerism, or spatial isomerism, is a form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but ...
s, whose molecules differ in spatial orientation. This happens only if the molecule contains a
stereogenic center In a molecule, a stereocenter is a particular instance of a stereogenic element that is geometrically a point. A stereocenter or stereogenic center is any point in a molecule, though not necessarily an atom, bearing different Substituent, substi ...
, specifically a carbon atom that is
chiral Chirality is a property of important in several branches of science. The word ''chirality'' is derived from the (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its ; that is, i ...
(connected to four distinct molecular sub-structures). Those four bonds can have any of two configurations in space distinguished by their
handedness In human biology Human biology is an interdisciplinary area of academic study that examines humans through the influences and interplay of many diverse fields such as human genetics, genetics, human evolution, evolution, human physiology, physio ...

handedness
. In a simple open-chain monosaccharide, every carbon is chiral except the first and the last atoms of the chain, and (in ketoses) the carbon with the keto group. For example, the triketose H(CHOH)(C=O)(CHOH)H (glycerone,
dihydroxyacetone Dihydroxyacetone (DHA), also known as glycerone, is a simple saccharide (a triose) with formula . DHA is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beet A sugar beet i ...

dihydroxyacetone
) has no stereogenic center, and therefore exists as a single stereoisomer. The other triose, the aldose H(C=O)(CHOH)2H (
glyceraldehyde Glyceraldehyde (glyceral) is a triose is an aldotriose because the carbonyl group is at the end of the chain Image:Dihydroxyacetone.png">150px, Dihydroxyacetone is a ketone, ketotriose because the carbonyl group is the center of the chain. A tr ...

glyceraldehyde
), has one chiral carbon — the central one, number 2 — which is bonded to groups −H, −OH, −C(OH)H2, and −(C=O)H. Therefore, it exists as two stereoisomers whose molecules are mirror images of each other (like a left and a right glove). Monosaccharides with four or more carbons may contain multiple chiral carbons, so they typically have more than two stereoisomers. The number of distinct stereoisomers with the same diagram is bounded by 2''c'', where ''c'' is the total number of chiral carbons. The
Fischer projection The Fischer projection, devised by Emil Fischer in 1891, is a two-dimensional representation of a Three-dimensional space, three-dimensional organic molecule by Graphical projection, projection. Fischer projections were originally proposed for the ...

Fischer projection
is a systematic way of drawing the
skeletal formula The skeletal formula, also called line-angle formula or shorthand formula, of 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 ...
of an acyclic monosaccharide so that the handedness of each chiral carbon is well specified. Each stereoisomer of a simple open-chain monosaccharide can be identified by the positions (right or left) in the Fischer diagram of the chiral hydroxyls (the hydroxyls attached to the chiral carbons). Most stereoisomers are themselves chiral (distinct from their mirror images). In the Fischer projection, two mirror-image isomers differ by having the positions of all chiral hydroxyls reversed right-to-left. Mirror-image isomers are chemically identical in non-chiral environments, but usually have very different biochemical properties and occurrences in nature. While most stereoisomers can be arranged in pairs of mirror-image forms, there are some non-chiral stereoisomers that are identical to their mirror images, in spite of having chiral centers. This happens whenever the molecular graph is symmetrical, as in the 3-ketopentoses H(CHOH)2(CO)(CHOH)2H, and the two halves are mirror images of each other. In that case, mirroring is equivalent to a half-turn rotation. For this reason, there are only three distinct 3-ketopentose stereoisomers, even though the molecule has two chiral carbons. Distinct stereoisomers that are not mirror-images of each other usually have different chemical properties, even in non-chiral environments. Therefore, each mirror pair and each non-chiral stereoisomer may be given a specific monosaccharide name. For example, there are 16 distinct aldohexose stereoisomers, but the name "glucose" means a specific pair of mirror-image aldohexoses. In the Fischer projection, one of the two glucose isomers has the hydroxyl at left on C3, and at right on C4 and C5; while the other isomer has the reversed pattern. These specific monosaccharide names have conventional three-letter abbreviations, like "Glu" for glucose and "Thr" for
threose Threose is a four-carbon monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydr ...
. Generally, a monosaccharide with ''n'' asymmetrical carbons has 2''n'' stereoisomers. The number of open chain stereoisomers for an aldose monosaccharide is larger by one than that of a ketose monosaccharide of the same length. Every ketose will have 2(''n''−3) stereoisomers where ''n'' > 2 is the number of carbons. Every aldose will have 2(''n''−2) stereoisomers where ''n'' > 2 is the number of carbons. These are also referred to as epimers which have the different arrangement of −OH and −H groups at the asymmetric or chiral carbon atoms (this does not apply to those carbons having the carbonyl functional group).


Configuration of monosaccharides

Like many chiral molecules, the two stereoisomers of glyceraldehyde will gradually rotate the polarization direction of linearly
polarized light Polarization ( also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillation Oscillation is the repetitive variation, typically in time, of some measure about a central value (ofte ...
as it passes through it, even in solution. The two stereoisomers are identified with the prefixes - and -, according to the sense of rotation: -glyceraldehyde is
dextrorotatory Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circula ...
(rotates the polarization axis clockwise), while -glyceraldehyde is levorotatory (rotates it counterclockwise). The - and - prefixes are also used with other monosaccharides, to distinguish two particular stereoisomers that are mirror-images of each other. For this purpose, one considers the chiral carbon that is furthest removed from the C=O group. Its four bonds must connect to −H, −OH, −C(OH)H, and the rest of the molecule. If the molecule can be rotated in space so that the directions of those four groups match those of the analog groups in -glyceraldehyde's C2, then the isomer receives the - prefix. Otherwise, it receives the - prefix. In the Fischer projection, the - and - prefixes specifies the configuration at the carbon atom that is second from bottom: - if the hydroxyl is on the right side, and - if it is on the left side. Note that the - and - prefixes do not indicate the direction of rotation of polarized light, which is a combined effect of the arrangement at all chiral centers. However, the two enantiomers will always rotate the light in opposite directions, by the same amount. See also system.


Cyclisation of monosaccharides

A monosaccharide often switches from the acyclic (open-chain) form to a
cyclic Cycle or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in social scienc ...
form, through a
nucleophilic additionIn organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atom ...
reaction between the carbonyl group and one of the hydroxyls of the same molecule. The reaction creates a ring of carbon atoms closed by one bridging
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
atom. The resulting molecule has a
hemiacetal A hemiacetal or a hemiketal have the general formula R1R2C(OH)OR, where R1 or R2 is hydrogen or an organic substituent. They generally result from the addition of an alcohol File:Alcohol general.svg, upright=0.8, The bond angle between a hydrox ...

hemiacetal
or
hemiketal of a hemiacetal Image:Hemiketal-2D-skeletal.png, 150px, Hemiketal A hemiacetal or a hemiketal is a compound that results from the addition of an alcohol File:Alcohol general.svg, upright=0.8, The bond angle between a hydroxyl group (-OH) and ...

hemiketal
group, depending on whether the linear form was an aldose or a ketose. The reaction is easily reversed, yielding the original open-chain form. In these cyclic forms, the ring usually has five or six atoms. These forms are called
furanose A furanose is a collective term for carbohydrates is a disaccharide found in animal milk. It consists of a molecule of galactose, D-galactose and a molecule of glucose, D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a bio ...
s and
pyranosePyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. There may be other carbons external to the ring. The name derives from its similarity ...
s, respectively — by analogy with
furan Furan is a heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemist ...

furan
and
pyran In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they underg ...

pyran
, the simplest compounds with the same carbon-oxygen ring (although they lack the double bonds of these two molecules). For example, the aldohexose
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
may form a hemiacetal linkage between the aldehyde group on carbon 1 and the hydroxyl on carbon 4, yielding a molecule with a 5-membered ring, called
glucofuranose Glucose is a simple sugar with the Chemical formula#Molecular formula, molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water ...

glucofuranose
. The same reaction can take place between carbons 1 and 5 to form a molecule with a 6-membered ring, called
glucopyranose Glucose is a simple 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 sucrose, a disaccharide composed of glucose and ...

glucopyranose
. Cyclic forms with a seven-atom ring (the same of
oxepane
oxepane
), rarely encountered, are called
heptose A heptose is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many ...
s. For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three. Cyclization creates a new
stereogenic In a molecule, a stereocenter is a particular instance of a stereogenic element that is geometrically a point. A stereocenter or stereogenic center is any point in a molecule, though not necessarily an atom, bearing different substituents, suc ...
center at the carbonyl-bearing carbon. The −OH group that replaces the carbonyl's oxygen may end up in two distinct positions relative to the ring's midplane. Thus each open-chain monosaccharide yields two cyclic isomers (
anomer An anomer is a type of geometric variation found at certain atoms in 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 carboh ...
s), denoted by the prefixes α- and β-. The molecule can change between these two forms by a process called
mutarotation Mutarotation is the change in the ''optical rotation Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization (waves), polarization about the optical axis of l ...
, that consists in a reversal of the ring-forming reaction followed by another ring formation.


Haworth projection

The stereochemical structure of a cyclic monosaccharide can be represented in a
Haworth projection 275px, Haworth projection of the structures for α-D-glucopyranose and L-Glucose, α-L-glucopyranose. A Haworth projection is a common way of writing a structural formula to represent the cyclic molecular geometry, structure of monosaccharides with ...
. In this diagram, the α-isomer for the
pyranosePyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. There may be other carbons external to the ring. The name derives from its similarity ...
form of a -aldohexose has the −OH of the
anomeric carbon An anomer is a type of geometric variation found at certain atoms in 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 carbohy ...
below the plane of the carbon atoms, while the β-isomer has the −OH of the anomeric carbon above the plane. Pyranoses typically adopt a chair conformation, similar to that of
cyclohexane Cyclohexane is a cycloalkane with the molecular formula C6H12. Cyclohexane is non-polar. Cyclohexane is a colorless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cycloh ...

cyclohexane
. In this conformation, the α-isomer has the −OH of the anomeric carbon in an axial position, whereas the β-isomer has the −OH of the anomeric carbon in equatorial position (considering -aldohexose sugars). Alpha-D-Glucopyranose.svg, α--Glucopyranose Beta-D-Glucopyranose.svg, β--Glucopyranose


Derivatives

A large number of biologically important modified monosaccharides exist: *
Amino sugar In organic chemistry, amines (, ) are compounds and functional group In organic chemistry, a functional group is a substituent or moiety in a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pent ...
s such as: **
galactosamine
galactosamine
**
glucosamine Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organism In biology, an organism (from Ancien ...

glucosamine
**
sialic acid Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Sweden, Swedish biochemist Gunnar Blix in 1952. The most common member of ...

sialic acid
**
''N''-acetylglucosamine
''N''-acetylglucosamine
* Sulfosugars such as: ** sulfoquinovose * Others such as: **
ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a 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 carb ...

ascorbic acid
**
mannitol Mannitol is a type of sugar alcohol Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific dis ...
**
glucuronic acid Glucuronic acid (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 a ...

glucuronic acid


See also

* Monosaccharide nomenclature *
Reducing sugar A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group. All monosaccharides are reducing sugars, along with some disaccharides, some oligosaccharides, and some polysac ...

Reducing sugar
*
Sugar acidA Sugar acid or acidic sugar is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble ca ...
*
Sugar alcohol Sugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) 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 ...
*
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 A disaccharide (also called a double sugar or ''biose'') is the sugar formed wh ...


Notes


References

* McMurry, John. Organic Chemistry. 7th ed. Belmont, CA: Thomson Brooks/Cole, 2008. Print.


External links


Nomenclature of Carbohydrates
{{Authority control Carbohydrate chemistry