Number of ATP generated in one TCA cycle ?
Ans. is 'c' i.e., 10 In a single TCA cycle 10 molecules of ATP are produced (12 molecules according to older calculations). One turn of the TCA cycle, staing with acetyl CoA produces 10 ATPs. When the staing molecule is pyruvate, the oxidative decarboxylation of pyruvate, the oxidative decarboxylation of pyruvate yields 2.5 ATPs and therefore, 12.5 ATPs are produced when staing compound is pyruvate. Since, two molecules of pyruvate enter the TCA cycle when glucose is metabolized (glycolysis produces 2 molecules of pyruvate), the number of ATPs is doubled. Therefore, 25 ATP molecules, per glucose molecule, are produced when pyruvate enters the TCA cycle. Note : Previously calculations were made assuming that NADH produces 3 ATPs and FADH generates 2 ATPs. This will amount a net generation of 30 ATP molecules in TCA per molecule glucose and total 38 molecules from staing. Recent experiments show that these values are overestimates and NADH produces 2.5 ATPs and FADH produces 1.5 ATPs. Therefore, net generation during TCA is 25 ATPs and complete oxidation of glucose through glycolysis plus citric acid cycle yield a net 32 ATPs. Energy yield (number of ATP generated) per molecule of glucose when it is completely oxidized through glycolysis plus citric acid cycle, under aerobic conditions, is as follows :-
2
8
10
11