Pentose pathway produces -
Ans. is 'b' i.e., NADPH Hexose monophosphate shunt (HMP) or pentose phosphate pathway (PPP)o HMP is an alternative route for the oxidation of glucose (beside glycolysis).o It is also called as "pentose phosphate pathway", "Dickens - Horecker pathway", "Shunt pathway" or "phosphogluconate oxidative pathway".o HMP shunt is required for provision of reduced NADPH and fiver-carbon sugars (Pentose phosphates) for nucleic acid synthesis. Normally, 90% of glucose is oxidized by glycolysis and 10% is oxidized by HMP shunt.o However, in liver and RBCs HMP shunt accounts for oxidation of 30% glucose.o HMP shunt occurs in the cytosol.o It is highly active in liver, adipose tissue, adrenal cortex, lens, cornea, lactating (but not the nonlactating) mammary gland, Gonads0 (testis , ovary) and erythrocytes,o Activity of this pathway is minimal in muscle and brain, where almost all of the glucose is degraded by glycolysis.Reactions of the HMP shunto HMP shunt is a multicyclic process in which 3 molecules of glucose-6-phosphate give rise to 3 molecules of CO2 and 3 molecules of 5-carbon sugars (ribulose-5-phosphate).o The latter are rearranged to generate 2 molecules of glucose-6-phosphate (through fructose-6-phosphate) and 1 molecule glyceraldehyde-3-phosphate.o HMP shunt does not generate ATP3 Glucose-6-phosphate + 6 NADP - 2 glucose-6-phosphate + 1 glyceraldehyde-3-phosphate + 6 NADPH +3CO2o The reaction of HMP shunt are divided into two phases : - 1) Phase I (Oxidative irreversible phase): - During this phase, 3 molecules of glucose-6-phosphate are oxidized with generation of 6 molecules of NADPH, and three molecules of pentose phosphate (ribulose-5-phosphate), with liberation of three molecules of CO2. Metabolites produced during this phase are 6- phosphoglucanolactone, 6-phosphogluconate and ribulose-5-phosphate. ii) Phase II (Non-oxidative reversible phase): - During this phase, pentose phosphate is converted to intermediates of glycolysis, i.e., glucose-6-phosphate and glyceraldehyde-3-phosphatec. Intermediary metabolites of this phase are xylulose-5-phosphatee, ribose-5-phosphate, sedoheptulose-7-phosphate, erythrose-4-phosphate and fructose-6-phosphate.
ATP
NADPH
ADP
AcetylCoA
HMP Shunt Pathway, Fructose, Galactose Metabolism