Question

The end product of oxidative phosphorylation is………………………….
A. NADH
B. Oxygen
C. ADP
D. ATP + Water

Answer 1

The metabolic pathway through which the electron passes from one carrier to another is called the electron transport system and it is present in the inner mitochondrial membrane. Electron transport systems are also called oxidative phosphorylation.

Complete answer: 1. The respiratory breakdown of glucose in presence of oxygen is an oxidative process. During this process, several intermediates such as phosphoglyceraldehyde, pyruvic acid, iso citric acid, succinic acid, and malic acid are oxidized.
2. Electrons produced in the mitochondrial matrix during the citric acid cycle are oxidized by an NADH dehydrogenase (complex I), and electrons are then transferred to ubiquinone located within the inner membrane.
3. Ubiquinone also receives reducing equivalents via FADH2 that is generated during the oxidation of succinate in the citric acid cycle.
The reduced ubiquinone is then oxidized with the transfer of electrons to cytochrome bc1 complex
4. Cytochrome c is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for the transfer of electrons between complex III and complex IV. Complex IV refers to cytochrome c oxidase complex containing cytochromes a and a3, and two copper centers.
5. When the electrons pass from one carrier to another via complex I to IV in the electron transport chain, they are coupled to ATP synthase for the production of ATP molecules synthesized depending on the nature of the electron donor.
6. Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of ${FADH}_{2}$ produces 2 molecules of ATP.
7. So it can be concluded that the transfer of electrons to oxygen to form water in the mitochondrial electron transport chain is coupled to ATP synthesis from ADP and inorganic phosphate by the ATP synthase.

So the correct answer is option D. ATP and Water.

Note: Oxygen acts as the final hydrogen acceptor. Unlike phosphorylation where it is the light energy that is utilized for the production of proton gradient required for phosphorylation in respiration, it is the energy of oxidation-reduction utilized for the same process. It is for this reason that the process is called oxidative phosphorylation.