Question

The pentose phosphate pathway ismost tightly integrated with which metabolic pathway in
mammals?

(a) glycolysis
(b) TCA cycle
(c) tricarboxylate transport pathway
(d) fatty acid oxidation
(e) fatty acid elongation

Answer 1

Correct answer is a. Glycolysis

Pentose phosphate pathway is basically an anabolic pathway i.e pathway that requires energy to build up larger molecules that takes place in cytosol, Whereas glycolysis takes place in cytoplasm.

In this pathway, the first phase is the oxidative phase where NADPH is generated (required for cells) whereas in second phase 5 carbon sugar is synthesized which is non oxidative along with ribose- 5 phosphate (required for synthesis of DNA) which acts as presursor for synthesis of nucleotides. Basically, metabolism of glucose-6-phosphate by this pathway is linked with glycolysis metabolic pathway.

Glycolysis involves one investment step, where ATP is required for phosphorylation of the substrates and an energy yielding phase where ATP is produced via phosphorylation and in this step NAD+ is reduced to NADH. Thus, this glycolysis pathway gives 2 ATP and 2NADH molecules and this NADH further enters the electron transport chain where ATP is produced by oxidative phosphorylation.

Glycolysis breaks 6 carbon sugar into 3 carbon sugar, which is then oxidized to form two molecules of pyruvate.

Thus, glycolysis provides the first 6 carbon molecule to the pentose phosphate pathway. Glucose is converted to glucose-6-phosphate (by addition of phosphate group) and these molecules of glucose-6-phosphate can be used by pentose phosphate pathway.

In this way, Glycolysis and pentose phosphate pathway are tightly integrated with each other.