Question

Question #9 (10 points) - Explain the major functions (pleural) of the pentose phosphate pathway (pentose shunt). (Don't give the pathway)

Answer 1

Pentose phosphate pathway ( or hexose monophosphate pathway or phosphogluconate pathway) is an alternative pathway to glucose oxidation.The enzymes of the pentose phosphate pathway shunt are located in the cytosol and in the plastids.This pathway has two primary functions:

1) To provide NADPH for reductve biosynthesis.

NADPH and NADH are not metabolically interchangeable. NADH uses the free energy of metabolite oxidation to synthesize ATP( oxidative phosphorylation), whereas NADPH uses the free energy of metabolite oxidation for reduction biosynthesis.

NADPH from the pentose phosphate pathway serves as a source of electrons for reductive biosynthesis( such as biosynthesis of fatty acid, cholesterol and nucleotide) and detoxification( such as reduction of oxidized glutathione,the activity of cytochrome P450 monooxygenases).

2) To provide ribose 5 phosphate for nucleotide and nucleic acid biosynthesis.

The pathway synthesizes four-and five- carbon sugars for variety of purposes.The four carbon sugar erythose 4- phosphate is used to synthesize aromatic amino acids and vitamin B6 (pyridoxal). The pentose ribose 5- phosphate is major component of nucleicacids and ribulose 1,5,-bisphosphate is the primary CO2  acceptor in photosynthesis.

3) Intermediates in the pentose phosphate pathway may be used to produce ATP. Glyceraldehyde 3- phosphate from the pathway can enter the three -carbon stage of the glycolytic pathwawy and be converted to ATP and pyruvate.