Which of the following best describes the antioxidant activity of selenium in cellular respiration?

• A. Selenium acts as a cofactor for cytochrome c oxidase in the electron transport chain.
• B. Selenium is required for the synthesis of ATP from ADP and inorganic phosphate.
• C. Selenium is a component of glutathione peroxidase, an enzyme that reduces hydrogen peroxide to water.
• D. Selenium directly scavenges free radicals without the need for enzymes.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the role of selenium in cellular respiration. Selenium is a trace element that plays a critical role in antioxidant defense mechanisms within cells.
2. Step 2: Learn about glutathione peroxidase. Selenium is a key component of this enzyme, which is involved in reducing hydrogen peroxide (H₂O₂) to water (H₂O), thereby protecting cells from oxidative damage.
3. Step 3: Clarify why selenium does not act as a cofactor for cytochrome c oxidase. Cytochrome c oxidase is an enzyme in the electron transport chain, but selenium is not directly involved in this process.
4. Step 4: Explain why selenium is not required for ATP synthesis. ATP synthesis occurs through oxidative phosphorylation, primarily driven by the electron transport chain and ATP synthase, and selenium does not play a direct role in this mechanism.
5. Step 5: Address the misconception about selenium directly scavenging free radicals. Selenium does not act as a free radical scavenger itself; instead, it functions as part of enzymes like glutathione peroxidase to neutralize reactive oxygen species.