The number of ATPs generated in one turn of Krebs cycle are -
Ans. is A. o 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 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.nRecent 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 Pathway Step Enzyme Source Method of ATPformation No of ATPs gained pergiucose (new calculation) No of ATPs As per old calculation Glycolysis 1 Hexokinase - Minus 1 Minus 1 Do 3 Phosphofructokinase - Minus 1 Minus 1 Do 5 Glyceraldehyde-3-p DH NADH Respiratory chain 2.5 x 2 = 5 3*2= 6 Do 6 1,3-BPG kinase ATP Substrate level 1x2 = 2 1 *2= 2 Do 9 Pyruvate kinase ATP Substrate level 1 x2 = 2 1 *2= 2 Pyruvate to - Pyruvate NADH Respiratory chain 2.5x 2 = 5 3*2= 6 Acetyl CoA Dehydrogenase TCA cycle 3 Isocitrate DH NADH Respiratory chain 2.5x2 = 5 3*2= 6 Do 4 Alpha keto glutarate DH NADH Respiratory chain 2.5x2 = 5 3*2= 6 Do 5 Succinate thiokinase GTP Substrate level l x2 = 2 1 *2= 2 Do 6 Succicinate DHFADH2 Respiratory chain 1.5x2 = 3 2*2= 4 Do 8 Malate DH NADH Respiratory chain 2.5x2 = 5 3*2= 6 Net generation in glycolytic pathway Generation in pyruvate dehydrogenase reaction Generation in citric acid cycle Net generation of ATP from one glucose mole 9 minus 2 = 7 10 minus 2= 8 = 5 = 6 = 20 = 24 = 32 38
12
24
15
30
Respiratory Chain