ATPs generated in TCA cycle
Correct Answer: 10
Description: ATP Generating Steps in TCA Cycle There are 3 NADH molecules generated during one cycle, each of them will give rise to 2 1/2 ATPs on oxidation by electron transpo chain (ETC); so altogether they will give 3 x 2 1/2 = 7 1/2 (7.5) high energy phosphates. The FADH2 will generate 1 1/2 molecules of ATP. In addition, one molecule of GTP (equivalent to one molecule of ATP) is formed by substrate-level phosphorylation. Hence, per turn of the cycle, 10 high energy phosphates are produced. These steps are marked in Figure 18.5 and in Table 18.1. The summary is shown in Box 18.2. Note: Recent work shows that in the electron transpo chain, NADH produces only 2.5 ATPs and FADH only 1.5 ATPs. The old values (used in the Table 18.1. ATP generation steps Step Reactions no. CoATPs ATPs enzyme (old(new calculation) 3Isocitrate - -- Alpha-ketoglutarate dehydrogenase reaction is the only one irreversible step in the cycle. The free energy changes of the reactions of the cycle are such that the cycle will operate spontaneously in the clockwise direction. Only about 33% of energy liberated is trapped as ATP. The rest is used to keep the body temperature at a higher level than the environment.Ref: DM Vasudevan Textbook of Medical Biochemistry, 6th edition, page no: 220
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