Question

When ADP levels are low, ___________.

A Option A: there is a sustained build-up in the proton-motive force B

Option B: all of the choices are correct

C Option C: the proton pumping reactions of the electron transport chain are inhibited

Option D: the consumption of oxygen by cytochrome oxidase is inhibited

Answer 1

Answer: option C and D, the proton pumping reaction of electron transport chain are inhibited and consumption of oxygen by cytochrome oxidase is inhibited.

Oxidative Phosphorylation or electron transport chain is the last step in aerobic cellular respiration. In this the reducing power in the form NADH and FADH is used to generate energy (ATP) The reducing power NADH and FADH2 in the matrix of mitochondria will pump the protons outside the inner membrane of mitochondria, this will generate a proton gradient and these protons will come back through ATP synthase back to the matrix and in the process the energy generated is used to phosphorylate ADP to ATP. This is called oxidative phosphrylation. This is the chemiosmotic theory for energy generation.

Electron transport will give rise to pumping of protons and it is coupled to Phosphorylation of ADP. Hence the most important factor which determines the rate of oxidative Phosphorylation is ADP.

The last electron transfer(in ETC) from cytochrome oxidase to oxygen is dependent on the presence of ADP. Electrons will not flow in ETC to oxygen unless there is need of ATP. Need of ATP is judged by the presence of ADP hence more the amount of ADP more transfer of electrons to oxygen takes place.

Hence when ADP levels are low proton pumping reaction of electron transport chain are inhibited and consumption of oxygen by cytochrome oxidase is inhibited and in the process ATP generation will be inhibited.