Question

Oxidative phosphorylation is

• A. formation of ATP by transfer of phosphate group from a substrate to ADP
• B. oxidation of phosphate group in ATP
• C. addition of phosphate group to ATP
• D. formation of ATP by energy released from electrons removed during substrate oxidation

Answer 1

The Correct Option is D

Oxidative phosphorylation is a crucial process that occurs in the mitochondria of eukaryotic cells and is essentially the final step of cellular respiration. Let's break down the details of this process to better understand why option four is the correct choice.

During oxidative phosphorylation:

1. Electrons are transferred from NADH and FADH₂ (produced in earlier stages of cellular respiration) to oxygen via a series of electron carriers in the electron transport chain.
2. As electrons move through the electron transport chain, the energy released is used to pump protons from the mitochondrial matrix to the intermembrane space, creating a proton gradient (also known as a proton motive force).
3. This gradient creates a potential energy difference across the inner mitochondrial membrane.
4. ATP synthase, an enzyme located in the inner mitochondrial membrane, uses this proton gradient to synthesize ATP from ADP and inorganic phosphate. This process is called chemiosmosis.

The key point is that the energy for ATP synthesis is derived from the energy released during electron transport chain reactions, which is fundamentally a series of oxidation-reduction reactions. Hence, the ATP is formed using energy released from electrons that are removed during substrate oxidation.

Now, let's justify why the other options are incorrect:

• Option 1: "Formation of ATP by transfer of phosphate group from a substrate to ADP" - This describes substrate-level phosphorylation, not oxidative phosphorylation.
• Option 2: "Oxidation of phosphate group in ATP" - This process does not accurately describe any major metabolic pathway relevant to ATP synthesis.
• Option 3: "Addition of phosphate group to ATP" - This is incorrect because ATP is phosphorylated from ADP, not from existing ATP.

In conclusion, the correct answer is indeed the fourth option: "Formation of ATP by energy released from electrons removed during substrate oxidation."