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In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. [1] The chemical formula of many pentoses is C 5 H 10 O 5, and their molecular weight is 150.13 g/mol. [2] Pentoses are very important in biochemistry. Ribose is a constituent of RNA, and the related molecule, deoxyribose, is a constituent of DNA.
Monosaccharides can be classified by the number x of carbon atoms they contain: triose (3), tetrose (4), pentose (5), hexose (6), heptose (7), and so on. Glucose, used as an energy source and for the synthesis of starch, glycogen and cellulose, is a hexose. Ribose and deoxyribose (in RNA and DNA, respectively) are pentose
The elementary formula of a simple monosaccharide is C n H 2n O n, where the integer n is at least 3 and rarely greater than 7. Simple monosaccharides may be named generically based on the number of carbon atoms n: trioses, tetroses, pentoses, hexoses, etc.
Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula C 5 H 10 O 5. Two enantiomers are possible, d-ribulose (d-erythro-pentulose) and l-ribulose (l-erythro-pentulose). d-Ribulose is the diastereomer of d-xylulose.
Common conformations are chair (C), boat (B), skew (S), half-chair (H) or envelope (E). The ring atoms are then numbered; the anomeric, or hemiacetal, carbon is always 1. Oxygen atoms in the structure are, in general, referred to by the carbon atom they are attached to in the acyclic form, and designated O. Then:
The atom numbering convention is used to identify the carbons and nitrogens within a cyclic nucleotide. In the pentose, the carbon closest to the carbonyl group is labeled C-1. When a pentose is connected to a nitrogenous base, carbon atom numbering is distinguished with a prime (') notation, which differentiates these carbons from the atom ...
Specifically, it is the phosphodiester bonds that link the 3' carbon atom of one sugar molecule and the 5' carbon atom of another (hence the name 3', 5' phosphodiester linkage used with reference to this kind of bond in DNA and RNA chains). [3] The involved saccharide groups are deoxyribose in DNA and ribose in RNA.
Enzyme AICAR transformylase assists in the final carbon transfer from N10-formyltetrahydrofolate, forming N-formylaminoimidazole-4-carboxamide ribonucleotide (FAICAR). Lastly, closure of the second ring structure is carried out by IMP synthase to form IMP, where IMP fate would lead to the formation of a purine nucleotide.