A carbohydrate is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 and thus with the empirical formula Cm(H2O)n, which does not mean the H has covalent bonds with O. However, not all carbohydrates conform to this precise stoichiometric definition, nor are all chemicals that do conform to this definition automatically classified as carbohydrates.
Monosaccharides, also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.
Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life-forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.
Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide with idealized formula H−(C=O)−(CH2)−(CHOH)3−H. Its name indicates that it is a deoxy sugar, meaning that it is derived from the sugar ribose by loss of a hydroxy group. Discovered in 1929 by Phoebus Levene, deoxyribose is most notable for its presence in DNA. Since the pentose sugars arabinose and ribose only differ by the stereochemistry at C2′, 2-deoxyribose and 2-deoxyarabinose are equivalent, although the latter term is rarely used because ribose, not arabinose, is the precursor to deoxyribose.
In chemistry, a hexose is a monosaccharide (simple sugar) with six carbon atoms. The chemical formula for all hexoses is C6H12O6, and their molecular weight is 180.156 g/mol.
An aldose is a monosaccharide with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ketoses, which have the carbonyl group away from the end of the molecule, and are therefore ketones.
A biomolecule or biological molecule is a loosely used term for molecules present in organisms that are essential to one or more typically biological processes, such as cell division, morphogenesis, or development. Biomolecules include the primary metabolites which are large macromolecules such as proteins, carbohydrates, lipids, and nucleic acids, as well as small molecules such as vitamins and hormones. A more general name for this class of material is biological materials. Biomolecules are an important element of living organisms, those biomolecules are often endogenous, produced within the organism but organisms usually need exogenous biomolecules, for example certain nutrients, to survive.
In chemistry, a phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. The "bond" involves this linkage C−O−PO−2O−C. Discussion of phosphodiesters is dominated by their prevalence in DNA and RNA, but phosphodiesters occur in other biomolecules, e.g. acyl carrier proteins.
In biochemistry, a ribonucleotide is a nucleotide containing ribose as its pentose component. It is considered a molecular precursor of nucleic acids. Nucleotides are the basic building blocks of DNA and RNA. Ribonucleotides themselves are basic monomeric building blocks for RNA. Deoxyribonucleotides, formed by reducing ribonucleotides with the enzyme ribonucleotide reductase (RNR), are essential building blocks for DNA. There are several differences between DNA deoxyribonucleotides and RNA ribonucleotides. Successive nucleotides are linked together via phosphodiester bonds.
A diol is a chemical compound containing two hydroxyl groups. An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified.
A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 (aldotetroses) or a ketone functional group in position 2 (ketotetroses).
The pentose phosphate pathway is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While the pentose phosphate pathway does involve oxidation of glucose, its primary role is anabolic rather than catabolic. The pathway is especially important in red blood cells (erythrocytes). The reactions of the pathway were elucidated in the early 1950s by Bernard Horecker and co-workers.
Transketolase is an enzyme that, in humans, is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P). The abstraction of two carbons from D-xylulose-5-P yields the 3-carbon aldose glyceraldehyde-3-P. In the Calvin cycle, transketolase catalyzes the reverse reaction, the conversion of sedoheptulose-7-P and glyceraldehyde-3-P to pentoses, the aldose D-ribose-5-P and the ketose D-xylulose-5-P.
A deoxyribonucleotide is a nucleotide that contains deoxyribose. They are the monomeric units of the informational biopolymer, deoxyribonucleic acid (DNA). Each deoxyribonucleotide comprises three parts: a deoxyribose sugar (monosaccharide), a nitrogenous base, and one phosphoryl group. The nitrogenous bases are either purines or pyrimidines, heterocycles whose structures support the specific base-pairing interactions that allow nucleic acids to carry information. The base is always bonded to the 1'-carbon of the deoxyribose, an analog of ribose in which the hydroxyl group of the 2'-carbon is replaced with a hydrogen atom. The third component, the phosphoryl group, attaches to the deoxyribose monomer via the hydroxyl group on the 5'-carbon of the sugar.
Sugar phosphates are often used in biological systems to store or transfer energy. They also form the backbone for DNA and RNA. Sugar phosphate backbone geometry is altered in the vicinity of the modified nucleotides.
The Kiliani–Fischer synthesis, named for German chemists Heinrich Kiliani and Emil Fischer, is a method for synthesizing monosaccharides. It proceeds via synthesis and hydrolysis of a cyanohydrin, followed by reduction of the intermediate acid to the aldehyde, thus elongating the carbon chain of an aldose by one carbon atom while preserving stereochemistry on all the previously present chiral carbons. The new chiral carbon is produced with both stereochemistries, so the product of a Kiliani–Fischer synthesis is a mixture of two diastereomeric sugars, called epimers. For example, D-arabinose is converted to a mixture of D-glucose and D-mannose.
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers.
Monosaccharide nomenclature is the naming system of the building blocks of carbohydrates, the monosaccharides, which may be monomers or part of a larger polymer. Monosaccharides are subunits that cannot be further hydrolysed in to simpler units. Depending on the number of carbon atom they are further classified into trioses, tetroses, pentoses, hexoses etc., which is further classified in to aldoses and ketoses depending on the type of functional group present in them.
In organic chemistry, a cyclitol is a cycloalkane containing at least three hydroxyl, each attached to a different ring carbon atom. The general formula for an unsubstituted cyclitol is C
nH
2n-x(OH)
x or C
nH
2nO
x where 3 ≤ x ≤ n.
Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 and the linear-form composition H−(C=O)−(CHOH)4−H. The naturally-occurring form, d-ribose, is a component of the ribonucleotides from which RNA is built, and so this compound is necessary for coding, decoding, regulation and expression of genes. It has a structural analog, deoxyribose, which is a similarly essential component of DNA. l-ribose is an unnatural sugar that was first prepared by Emil Fischer and Oscar Piloty in 1891. It was not until 1909 that Phoebus Levene and Walter Jacobs recognised that d-ribose was a natural product, the enantiomer of Fischer and Piloty's product, and an essential component of nucleic acids. Fischer chose the name "ribose" as it is a partial rearrangement of the name of another sugar, arabinose, of which ribose is an epimer at the 2' carbon; both names also relate to gum arabic, from which arabinose was first isolated and from which they prepared l-ribose.
