How many molecules of NADH are produced directly from the citric acid cycle?

In one complete turn of the citric acid cycle, three molecules of NADH are generated. The cycle begins with the condensation of acetyl-CoA and oxaloacetate, forming citrate, and it undergoes a series of enzymatic transformations. During this process, particular steps lead to the reduction of NAD+ to NADH.

1. At the isocitrate dehydrogenase step, isocitrate is converted to α-ketoglutarate, resulting in the production of one NADH molecule.

2. Subsequently, in the conversion of α-ketoglutarate to succinyl-CoA, another NAD+ molecule is reduced to NADH, yielding a second molecule of NADH.

3. In the conversion of malate to oxaloacetate, the final step of the cycle, another reaction occurs that reduces NAD+ to NADH, producing the third molecule.

This means that in total, three NADH molecules are produced per turn of the cycle, which is an essential outcome since NADH plays a critical role in the electron transport chain, ultimately leading to ATP production.