Q.Give a detailed, step-by-step account of the tricarboxylic acid (TCA) cycle, from the formation of citric acid to the regeneration of oxaloacetic acid, and state the total number of carbon dioxide molecules released, NADH and FADH2 generated, and ATP captured, over the two turns of the cycle corresponding to one glucose molecule.

[!TLDR]

One turn: acetyl CoA + OAA to citrate to isocitrate to (2 oxidative decarboxylations, 2 CO2 + 2 NADH) succinyl CoA to (1 ATP/GTP) succinate to (FADH2) fumarate to malate to (NADH) OAA. Per turn: 2 CO2, 3 NADH, 1 FADH2, 1 ATP. Per glucose (2 turns): 4 CO …

Each turn of the TCA cycle, in the mitochondrial matrix, begins when acetyl CoA combines with oxaloacetic acid (OAA, 4C), catalysed by citrate synthase, to form citric acid (6C), releasing coenzyme A. Citric acid is rearranged to isocitric acid, which is then oxidatively decarboxylated (1 NAD+ to NADH, 1 CO2 released) to alpha-ketoglutaric acid (5C); this in turn is oxidatively decarboxylated a second time (a second NAD+ to NADH, a second CO2 released) to succinyl CoA (4C, bound to CoA). Succinyl CoA is converted to succinic acid, capturing the cycle's only direct substrate-level phosphorylation as 1 GTP (equivalent to 1 ATP). Succinic acid is oxidised by succinate dehydrogenase (using FAD, not NAD+) to fumaric acid, reducing FAD to FADH2; fumaric acid is hydrated to malic acid, which is finally oxidised (a fourth NAD+ to NADH) back to oxaloacetic acid, regenerating the compound the turn began with. …

Walk through the cycle step by step from citrate synthase to the regeneration of OAA, noting where CO2, NADH, FADH2 and ATP are each produced, then double …

Reporting the per-turn totals (2 CO2, 3 NADH, 1 FADH2, 1 ATP) as the per-glucose totals, forgetting the cycle …