Number of ATP generated in one TCA cycle-
Ans. is 'c' i.e., 10 o In a single TCA cycle 10 molecules of ATP are produced (12 molecules according to older calculations),o One turn of the TCA cycle, starting with acetyl Co A produces 10 ATPs. When the starting 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 starting 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,o 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 starting. 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.o 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 :- Method of ATP formationNo of ATPs gained perglucose (new calculation)No of ATPs As per old calculationPathwayStepEnzymeSourceGlycolysis1Hexokinase- Minus1Minus 1Do3Phosphofructokinase- Minus1Minus IDo5Glyceraldehyde-3-p DHNADHRespiratory chain2.5x2 =53x2=6Do61J-BPG kinaseATPSubstrate level1x2 =21x2=2Do9Pyruvate kinaseATPSubstrate level1x2 =21x2=2Pyruvate to Acetyl CoA-PyruvateDehydrogenaseNADHRespiratory chain2.5 x 2 =53x2=6 TCA cycle3Isocitrate DHNADHRespiratory chain2.5 x 2 =53x2=6Do4Alpha keto glutarate DHNADHRespiratory chain2.5 x 2 =53x2=6Do5Succinate thiokinaseGTPSubstrate level1x2 =21x2=2Do6Succicinate DHFADH2Respiratory chain1.5 x 2 =32x2=4Do8Mai ate DHNADHRespiratory chain2.5 x 2 =53 x 2= 6Net generation in glycolytic pathway 9 minus 2=710 minus 2=8Generation in pyruvate dehydrogenase reaction=5=6Generation In citric acid cycle=20=24Net generation of ATP from one glucose mole=32=38
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5
10
11
Kerbs Cycle