Preferred Label : Oxidative Reactions of the Pentose Phosphate Pathway;
NCIt synonyms : NADPH Pathway; Oxidative Phase of the Pentose Phosphate Pathway;
Alternative definition : BIOCARTA: One form of chemical energy used to drive biosynthetic reactions forward
is the reducing power of the energy carrier NADPH. NADPH is essential to drive the
biosynthesis of fatty acids and cholesterol for example. While NADPH is an important
energy carrier and is closely related to the high-energy electron carrier NADH, NADPH
is distinct from NADH in several ways. NADH in oxidative phosphorylation in mitochondria
transports chemical energy from the Kreb's cycle to the electron transport chain,
but NADPH does not play this role. The cell keeps its pools of NADH and NADPH isolated
biochemically, through the specificity of the enzymes that use and generate these
cofactors. Enzymes that metabolize NADH and NADPH are highly specific for one cofactor
or the other and are in different pathways. While NADH is produced in mitochondria
by the Kreb's cycle, NADPH is produced through a pathway called the pentose phosphate
pathway. Since one of the main purposes of this pathway is to produce NADPH for biosynthesis,
this pathway occurs most predominantly in tissues like liver, fat cells, or adrenal
glands that are involved in fatty acid and cholesterol biosynthesis. This pathway
starts with glucose-6-phosphate, the first committed step in glycolysis, and can provide
an alternative route to glycolysis for energy production. The first portion of the
pentose phosphate pathway involves the oxidation of glucose in three steps, with the
concomitant production of NADPH. The first step in the pentose phosphate pathway is
catalyzed by glucose-6-phosphate dehydrogenase. In normal red blood cells, the NADPH
produced by glucose-6-phosphate dehydrogenase is used to regenerate glutathione and
protect cell membranes. Genetic deficiency in the activity of this enzyme is very
common in some populations, and can result in anemias caused by fragile red blood
cells. In the second and third steps, further oxidation makes more NADPH and releases
carbon dioxide, shortening the sugar from six carbons to five (D-ribulose 5-phosphate).
After isomerization, D-ribose 5-phosphate is produced and provides the starting point
for a series of reactions that converts the 5-carbon ribose into 6-carbon fructose-6-phosphate
and 3-carbon glyceraldehyde-3-phosphate. Ribose is also used to make nucleotides for
RNA and DNA. (This definition may be outdated - see the DesignNote.);
NCIt note : The BIOCARTA Definition (ALT_DEFINITION) for this pathway concept was provided by
BioCarta. This property was not created by, nor is it maintained by the NCI Thesaurus
staff. Additionally, BioCarta is no longer updating its pathway data; thus, the BIOCARTA
Definition might be outdated or inaccurate. Please see the Terms and Conditions for
Use at http://www.biocarta.com/.;
Biocarta ID : pentosePathway;
Origin ID : C91327;
UMLS CUI : C2984167;
Semantic type(s)
- has_gene_product_element
- pathway_has_gene_element
