The ATPase Synthase Complex Q12.1: Why are 4 H needed for every ATP synthesized and exported by mitochondria, even though only 3 H need to be translocated by the ATP Synthase Complex to synthesize one ATP

1 H is consumed in exchanging the synthesized ATP in mitochondria with ADP in cytosol by adenine nucleotide translocator (ANT).

Explanation:

The electrons from NADH and FADH2 are transported in electron transport chain through various complexes that act as electron transporter, to oxygen. In this process, the pumping of protons from mitochondrial matrix to intermembrane space causes a concentration gradient and hydrogen ions diffuses out of matrix space through ATP synthase causing the production of ATP.

3 H are enough to pass through ATP synthase for the phosphorylation of ADP to produce ATP. 1 H or 25% of energy yielded from electron transfer is required to exchange the matrix ATP with the ADP in intermembrane space by adenine nucleotide translocator (ANT). This process provides continuous supply of ADP to mitochodaria and ATP which is exported to cytosol is utilized by cell to perform various functions. There will be no ATP production in mitochondria without ADP. So 4 H are required for 1 ATP production.

1 H for importing ADP to mtichodaria + 3 H for phosphorylation of ADP to ATP