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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.
The pentose phosphate pathway. The pentose phosphate pathway (also called the phosphogluconate pathway and the hexose monophosphate shunt or HMP shunt) is a metabolic pathway parallel to glycolysis. [1] It generates NADPH and pentoses (five-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. [1]
Carbon atoms from ribose in PRPP form the linear chain and part of the imidazole ring in histidine. [ 15 ] [ 16 ] [ 17 ] The same is true for the biosynthesis of tryptophan, with the first step being N-alkylation of anthranilic acid catalysed by the enzyme anthranilate phosphoribosyltransferase .
These prefixes are attached to the systematic name of the molecular graph. So for example, D-glucose is D-gluco-hexose, D-ribose is D-ribo-pentose, and D-psicose is D-ribo-hexulose. Note that, in this nomenclature, mirror-image isomers differ only in the ' D '/' L ' prefix, even though all their hydroxyls are reversed.
The pentose phosphate pathway has two metabolic functions: (1) generation of nicotinamide adenine dinucleotide phosphate (reduced NADPH), for reductive biosynthesis, and (2) formation of ribose, which is an essential component of ATP, DNA, and RNA. Transaldolase links the pentose phosphate pathway to glycolysis.
Examples include ribosomes, nucleosomes, and many enzymes. nucleosidase Any of a class of enzymes which catalyze the decomposition of nucleosides into their component nitrogenous bases and pentose sugars. [12] nucleoside An organic molecule composed of a nitrogenous base bonded to a five-carbon sugar (either ribose or deoxyribose).
Ribonucleotides can be synthesized in organisms from smaller molecules through the de novo pathway or recycled through the salvage pathway. In the case of the de novo pathway, both purines and pyrimidines are synthesized from components derived from precursors of amino acids, ribose-5-phosphates, CO 2, and NH 3. [17] [12] The synthesis of IMP.
It is formed by phosphogluconate dehydrogenase in the pentose phosphate pathway. [2] [3] Ribulose 5-phosphate is involved in various metabolic pathways. Ribulose 5-phosphate can be acted upon by phosphopentose isomerase to form ribose 5-phosphate, which is a precursor for nucleotide and co-factor biosynthesis. [2]