Question

For ATP synthesis by oxidative phosphorylation, the P/O ratios of NADH and FADH2 are ~2.5 and ~1.5, respectively. Explain how mitochondrial electron transport, ATP synthase, and other membrane processes account for these numbers?

Answer 1

2 molecules of acetyl CoA enter into Krebs cycle which on subsequent oxidation generate 6NADH2, 2FADH2.. When 6NADH2, 2FADH2 enter into the electron transport system generate 22ATP molecules. In one step, there is substrate level phosphorylation whch directly yield 2ATP molecules. So, during Krebs cycle, every 2 molecules of acetyl CoA enter into Krebs cycle 24 ATP molecules are generated. So, primarily it is a energy producing system. Since, Krebs cycle involves with both anabolic and catabolic processes, it is also described as amphibolic process.

Complete oxidation of one glucose molecule yields a net gain of 38ATP. Out of 38ATP molecules, 4ATP are obtained by direct substrate level phosphorylation, 30ATP through oxidation of NADH2 and 4ATP through oxidation of FADH2. Since, a large number of ATP molecules are produced in the mitochondria, they are called the ‘power houses of the cell’.