Question

The chemiosmotic theory of ATP synthesis in the chloroplasts and mitochondria is based on

• A. Proton gradient
• B. Accumulation of K ions
• C. Accumulation of Na ions
• D. Membrane potential

Answer 1

The correct option is A Proton gradient

The chemiosmotic theory explains how ATP is generated in the mitochondria via the electron transfer chain (ETC). ETC is an oxidative phosphorylation reaction taking place in the inner membrane of the mitochondria. It begins with NADH and $FAD{H}_2$ that loses electrons. These electrons are transferred along the chain. As each complex accepts electrons and passes it on, energy is released. This energy is used to pump the protons that move against the concentration gradient from the matrix of the mitochondria to the inner membrane space. Eventually, there is a high concentration of proton buildup in the membrane space and the protons try to move back into the matrix. However, the inner membrane is impermeable to protons. A proton motive force (PMF) is set up and ATP synthase undergoes the conformational change and uses the PMF to make ATP from ADP. ATP synthase allows the proton to diffuse back down their gradient.