Assuming all NADH is transferred to the mitochondria vis the malate-aspartate sh

Question

Assuming all NADH is transferred to the mitochondria vis the malate-aspartate shuttle, what is the net cost in terms of ATP when 3 molecules of glucose are directed to the pentose phosphate pathway at the level of glucose-6-phosphate rather than continuing through glycolysis?

NOTE: Feed the appropriate products of the oxidative and non-oxidative branch of the pentose phosphate pathway back into glycolysis at the appropriate time so that 3 glucose-molecules through the pentose phosphate pathway generate 5 molecules of pyruvate, while the 3 glucose molecules from glycolysis generate 6 molecules of pyruvate. Stop metabolism at pyruvate. SHOW ALL WORK

Explanation / Answer

When one molecule of glucose is directed to pentose phosphate pathway, 2 NADPH and one CO2 are generated, in the oxidative phase. In this , first glucose converts to glucose6-phosphate, and then glucose 6 phosphate converts to ribose5-phosphate. Through non- oxidative pathway, ribose 5-phosphate is converts into various intermediates of glycosis (including pyruvate).

So, if 3 molecules of glucose are there, (2 NADPH *3)= 6 NADPH will be generated and 3 CO2 will be formed, in the oxidative phase. In the non - oxidative phase, 5 pyruvate molecules can be formed only, not 6

In terms of ATP, 6 NADPH can generate 6*3 = 18 ATP (theoritically)

In transferring , NADPH through mitochondrial membrane , one ATP is lost, so practically 6*2= 12 ATP should be generated.

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