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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]
Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ribulose 5-phosphate can reversibly isomerize to ribose 5-phosphate.
Phosphoribosyl pyrophosphate (PRPP) is a pentose phosphate. It is a biochemical intermediate in the formation of purine nucleotides via inosine-5-monophosphate, as well as in pyrimidine nucleotide formation. Hence it is a building block for DNA and RNA.
Ribose-5-phosphate isomerase deficiency (RPID) is a rare human disorder caused by mutations in ribose-5-phosphate isomerase, an enzyme of the pentose phosphate pathway.With only four known cases – all diagnosed between 1984 and 2019 – RPI deficiency is the second rarest disease, with Fields condition being the rarest, affecting two known individuals, Catherine and Kirstie Fields.
It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers (in this case structural isomers of pentose). It plays a vital role in biochemical metabolism in both the pentose phosphate pathway and the Calvin cycle. The systematic name of this enzyme class is D-ribose-5-phosphate aldose-ketose-isomerase.
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.
Phosphorylated pentoses are important products of the pentose phosphate pathway, most importantly ribose 5-phosphate (R5P), which is used in the synthesis of nucleotides and nucleic acids. Like some other monosaccharides, pentoses exist in two forms, open-chain (linear) or closed-chain (cyclic), that easily convert into each other in water ...
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]