A
pentose is a
monosaccharideMonosaccharides are the most basic units of biologically important carbohydrates. They are the simplest form of sugar and are usually colorless, water-soluble, crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose , fructose , galactose, xylose...
with five
carbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atomThe atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s. Pentoses are organized into two groups. Aldopentoses have an
aldehydeAn aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
functional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
at position 1. Ketopentoses have a
ketoneIn organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
functional group in position 2 or 3.
Aldopentoses
The aldopentoses have three chiral centers and therefore eight different stereoisomers are possible.
D-ArabinoseArabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde functional group.For biosynthetic reasons, most saccharides are almost always more abundant in nature as the "D"-form, or structurally analogous to D-glyceraldehyde.For sugars, the D/L...
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D-LyxoseLyxose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula 5105.Lyxose occurs only rarely in nature, for example, as a component of bacterial glycolipids.- See also :...
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D-RiboseRibose is an organic compound with the formula C5H10O5; specifically, a monosaccharide with linear form H––4–H, which has all the hydroxyl groups on the same side in the Fischer projection....
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D-XyloseXylose is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is the precursor to hemicellulose, one of the main constituents of biomass...
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L-ArabinoseArabinose is an aldopentose – a monosaccharide containing five carbon atoms, and including an aldehyde functional group.For biosynthetic reasons, most saccharides are almost always more abundant in nature as the "D"-form, or structurally analogous to D-glyceraldehyde.For sugars, the D/L...
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L-LyxoseLyxose is an aldopentose — a monosaccharide containing five carbon atoms, and including an aldehyde functional group. It has chemical formula 5105.Lyxose occurs only rarely in nature, for example, as a component of bacterial glycolipids.- See also :...
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L-RiboseRibose is an organic compound with the formula C5H10O5; specifically, a monosaccharide with linear form H––4–H, which has all the hydroxyl groups on the same side in the Fischer projection....
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L-XyloseXylose is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes an aldehyde functional group. It is the precursor to hemicellulose, one of the main constituents of biomass...
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Ketopentoses
The 2-ketopentoses have two chiral centers, and therefore four different stereoisomers are possible. The 3-ketopentoses are rare.
D-RibuloseRibulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105. Two enantiomers are possible, D-ribulose and L-ribulose . D-Ribulose is the diastereomer of D-xylulose.Ribulose sugars are composed in the...
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D-XyluloseXylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105. In nature, it occurs in both the L- and D-enantiomers.- Pathology :...
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L-RibuloseRibulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105. Two enantiomers are possible, D-ribulose and L-ribulose . D-Ribulose is the diastereomer of D-xylulose.Ribulose sugars are composed in the...
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L-XyluloseXylulose is a ketopentose, a monosaccharide containing five carbon atoms, and including a ketone functional group. It has the chemical formula 5105. In nature, it occurs in both the L- and D-enantiomers.- Pathology :...
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Properties
The aldehyde and ketone functional groups in these carbohydrates react with neighbouring
hydroxylA hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
functional groups to form
intramolecularIntramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...
hemiacetalHemiacetals and hemiketals are compounds that are derived from aldehydes and ketones respectively. The Greek word hèmi means half...
s and hemiketals, respectively. The resulting ring structure is related to
furanFuran is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans....
, and is termed a
furanoseA furanose is a collective term for carbohydrates that have a chemical structure that includes a five-membered ring system consisting of four carbon atoms and one oxygen atom...
. The ring spontaneously opens and closes, allowing rotation to occur about the bond between the carbonyl group and the neighbouring carbon atom — yielding two distinct configurations (α and β). This process is termed
mutarotationMutarotation is the change in the optical rotation that occurs by epimerization...
.
RiboseRibose is an organic compound with the formula C5H10O5; specifically, a monosaccharide with linear form H––4–H, which has all the hydroxyl groups on the same side in the Fischer projection....
is a constituent of
RNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
, and the related
deoxyriboseDeoxyribose, more, precisely 2-deoxyribose, is a monosaccharide with idealized formula H---3-H. Its name indicates that it is a deoxy sugar, meaning that it is derived from the sugar ribose by loss of an oxygen atom...
of
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
.
A
polymerA polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
composed of pentose sugars is called a
pentosan.
See also
- Triose
A triose is a monosaccharide, or simple sugar, containing three carbon atoms. There are only three possible trioses: L-Glyceraldehyde and D-Glyceraldehyde, both aldotrioses because the carbonyl group is at the end of the chain, and dihydroxyacetone, a ketotriose because the carbonyl group is in...
- Tetrose
A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
- Hexose
In organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C6H12O6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2....
- Heptose
A heptose is a monosaccharide with seven carbon atoms.They have either an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
- Pentose phosphate pathway
The pentose phosphate pathway is a process that generates NADPH and pentoses . There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars...
- The aniline acetate test
The aniline acetate test is a chemical test to identify the presence of certain carbohydrates. These carbohydrates may be converted to furfural, which reacts with aniline acetate to produce a bright pink color....
for distinguishing pentoses from other carbohydrates.