Number of ATPs formed per cycle of TCA -: (A) 10, (B) 24, (C) 8, (D) 30
Answer is A. Ans. is 'a' i.e., 10o Every turn of TCA cycle produces -i) 10 A TPs - If starting meterial is considered acetyl CoAii) 12 5 ATPs - It starting material is considered pyruvate.Energetics of TCA cycleso One turn of the TCA cycle, starting with acetyl CoA 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 cycleo 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 followsPathwayStep EnzymeSourceMethod of ATP formationNo of ATPs gained perglucose (new calculation)No of ATPs As per old calculationGlycolysis1 Hexokinase_ Minus 1Minus1Do3 Phosphofructokinase- Minus 1Minus1Do5 Glyceraldehyde-3-p DHNADHRespiratory chain2.5x2 =53x2=6Do6 1,3-BPG kinaseATPSubstrate level1x2 =21x2=2Do9 Pyruvate kinaseATPSubstrate level1 x 2 =21x2=2Pyruvate to Acetyl CoAPyruvateDehydrogenaseNADHRespiratory chain2.5 x 2 =53x2=6TCA cycle3 Isocitrate DHNADHRespiratory chain2.5 x 2 =53x2=6Do4 Alpha keto glutarate DHNADHRespiratory chain2.5 x 2 =53x2=6Do5 Succinate thiokinaseGTPSubstrate level1x2 =21x2=2Do6 Succicinate DHFADH2Respiratory chain1.5 x 2 =32x2= 4Do8 Malate DHNADHRespiratory chain2.5 x 2 =53x2= 6Net generation in glycolytic pathway9 minus 2=7 10 minus 2 = 8Generation in pyruvate dehydrogenase reaction=5= 6Generation in citric acid cycle=20= 24Net generation of ATP from one glucose mole=32= 38