Question

What supports the contention that proton gradient drives ATP formation in mitochondria? Explain the process of ATP synthesis?

Answer 1

In the aerobic respiration process the last process known as Electron Transport Chain (ETC) takes place in the mitochondria of the cell. The ETC is nothing but the creation of proton gradient through the proton pumping due to which ATP are synthesized in huge amount in the mitochondria. The ATP synthase present in the inner membrane of the mitochondria generates ATP when the proton moves in to the matrix of the mitochondria by proton pumping to create proton gradient and also spins the ATP synthase. This spin like movement of the ATP synthase converts the ADP in to ATP and produces ATP in the mitochondria.

Process of ATP synthesis :

Before knowing the process of ATP synthesis in the mitochondria, let us discuss the structure of the mitochondria first. The mitochondria are cell organelles which are present in each cell. Its number may vary from cell to cell as per the physiological function of the cell. As the cells of heart contains more number of mitochondria as compare to the cells of the skin. The mitochondria is double membrane bound organelle. The outer membrane allows the movement of the small molecules along with the ions. But the inner membrane is highly folded (crista) which don't allow the free flow movement of the small molecules and even of the ions. The molecules responsible for the movement of electron of the respiratory chain and the molecules responsible for synthesis of ATP which is ATP synthase or ATP synthatase are present in the inner membrane of the mitochondria. Also the inner membrane bound space of the mitochondria called matrix contains enzymes responsible for the Kreb's Cycle and hence resluts in the production of NADH and FADH2 which are used as substrate for the synthesis of ATP in mitochondria. Also the movement or exchange of charged metabolites are mediated by the carrier presents in the inner membrane of the mitochondria and are done on one-one exchange principle.

When the Hydrogen ion from FADH2 or NADH is transferred to Oxygen, the protons (Hydrogen ion) pumped across the crista/inner membrane of mitochondria hence converting the chemical energy of the previously synthesised substrate molecules in to electrical energy and also generates an electric potential across the membranes of the mitochondria. The electric pitential ranges fron 200 to 300 milivolt. The crista contains ATP synthase in them which can facilitates the binding of ADP, ATP and Pi to it. The ATP synthase has a special structure of polypeptides which forms a proton pore on the inner membrane of the mitochondria. When the ADP and Pi are attached to the ATP synthetase, the extra hydrogen ions formed outside the mitochondrial matrix flows back to the mitochondrial matrix resulting in the spinning of the ATP synthase and the production of ATP from the ADP and Pi. In this process again the electrical energy is converted in to chemical energy and are stored in the form of ATP. The rate of ATP synthesis depends upon the amount of ADP which can be supplied.

( I may have written ATP Synthatase instead of ATP Synthetase, please have a eye on this spelling mistake)