Suppose NAD is unavailable because NADH cannot be oxidized due to a mutation in the NADH dehydrogenase (Complex I). If FAD could substitute for all NAD, how would this affect the total ATP produced by the complete oxidation of glucose

FAD substitution will produce 28 ATP instead of 36.

Explanation:

NAD and FAD are coenzymes involved in reversible oxidation and reduction reactions. These compounds are also known as electron carriers. However NADH produce 3 electrons in electron transport chain and FADH2 produce 2 electron beacuase it transfer the electrons to second complex in ETC.

Normal prduction of ATP from glucose;

2 cytoplasmic NADH formed in glycolysis Each yields 2 ATP + 4

2 NADH formed in the oxidation of pyruvate Each yields 3 ATP + 6

2 FADH2 formed in the citric acid cycle Each yields 2 ATP + 4

6 NADH formed in the citric acid cycle Each yields 3 ATP + 18

2 ATP from glycolysis + 2

2 ATP from citric acid cycle + 2

Net yield ATP + 36

C6H12O6 + 6 CO2 + 36 ADP + 36 Pi ⇒6 CO2 + 6 H2O + 36 ATP

If we replace the NAD with FAD the total ATP production would be.

2 cytoplasmic FADH2 formed in glycolysis Each yields 2 ATP + 4

2 FADH2 formed in the oxidation of pyruvate Each yields 3 ATP + 4

2 FADH2 formed in the citric acid cycle Each yields 2 ATP + 4

6 FADH2 formed in the citric acid cycle Each yields 2 ATP + 12

2 ATP from glycolysis

+2

2 ATP from citric acid cycle + 2

Net yield ATP + 28

C6H12O6 + 6 CO2 + 28ADP + 28 Pi ⇒6 CO2 + 6 H2O + 28 ATP