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Question : What is the name of alternate way of glucose breakdown ? Explain the process involved in it.

Answer»

Solution :Pentose Phosphate phthway :
1. During RESPIRATION breakdown of glucose in cytosol occurs both by glycolysis (about 2/3) as well as by oxidative pentose phosphate pathway (about 1/3) . Pentose phosphate pathway was described by warburg Dicknes and LIPMANN (1938).
2. Hence, it is also called warburg -Dickens- Lipmann pathway . it takes place in cytoplasm of mature plant cells. it is an alternate way for breakdown of glucose.

3. It is also known as hexose monophosphate shunt (HMP shunt ) or direct Oxidative pathway. it consists of TWO phases, oxidative phase and non-oxidative phase.
4. The oxidative events convert six MOLECULES of six carbon glucose -6-phosphate to 6 molecules of five carbon sugar ribulose-5 phosphate with loss of `6CO_2` molecules and generation of 12 `NADPH+H^+` (not NADH).
5. The remaining reactions known as non-oxidative pathway convert ribolose -5- phosphate molecules to various intermediates such as ribose-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 regennerated. The overall reaction is :
`{:(6xx"glucose-6-phosphate"+12NADP^++6H_2O),(""darr),(5xx"glucose-6-Phosphate"+6CO_2+"pi"+12 NADPH+12H^+):}`
The net result of complete oxidation of one glucose-6-phosphate YIELD `6CO_2 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^+`.


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