Question

What is the name of alternate way to glucose breakdown? Explain the process in involved in it?

Answer 1

1. Pentose phosphate pathway is the alternate pathway for breakdown of glucose.
2. Pentose phosphate pathway was described by Warburg, Dickens and Lipmami (1938).
3. It is also known as Hexose monophosphate shunt (HMP shunt) or Direct oxidative phase and non – oxidative phase.
4. The oxidative phase convert six molecules of six carbon Glucose 6 phosphate to 6 molecules of five-carbon sugar Ribulose – 5 Phosphate with loss of 6CO₂ and generation of 12 NADPH + H⁺
5. Non oxidative pathway convert Ribulose – 5 – phosphate molecules to various intermediates such as Ribose – 5 – phosphate (5C), Xylulose – 5 – phosphate (5C), Glyceraldehyde – 3 – phosphate (3C), Sedoheptulose – 7 – phosphate (7C) and Erythrose – 4 – phosphate (4C).
6. Finally five molecules of glucose 6 – phosphate is regenerated
   \[\ce{6 x \underset{\text{↓}}{Glucose-6-Phosphate} + 12NADP+ + 6H2O}\]
   \[\ce{5 x glucose - 6 - phosphate + 6CO2 + Pi + 12 NADPH + 12H+}\]
   The net result of complete oxidation of one glucose – 6 – phosphate yield 6CO₂ and 12 NADPH + H⁺. The oxidative pentose phosphate pathway is controlled by glucose – 6 – phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to NADP^+.