Question

If the aspartate in ATP synthase that functions to shuttle protons across the inner mitochondrial membrane is mutated to glycine, ATP synthase function would be:

A) Decreased because the R group of glycine cannot change protonation state

B) Decreased because the R group of glycine is non-polar

C) Increased because the R group of glycine is smaller than the R group of aspartic acid, so more protons can flow

D) Unaffected because the R group of glycine is small enough to allow protons to continue to flow

The correct answer is A but i dont know why. Please explain

Answer 1

Ans a) Decreased because R group of glycine cannot change protonation state. The R group of glycine is very simple as it consists of only H. The R group of aspartate consists of CH₂-COO^-. The protonation state can be changed by the aspartate owing to its R group and hence helps ATP synthase in efficient movement of the protons across inner mitochondrial membrane. Due to H as R group, the protonation state cannot be changed by the glycine and hence retards the function of ATP synthase.