Which of the following does NOT scavenge free radicals in the lens?
**Core Concept:** Scavenging free radicals refers to the process of neutralizing reactive oxygen species (ROS) and reactive nitrogen species (RNS) that can damage cellular components and contribute to diseases like cataract, age-related macular degeneration, and atherosclerosis. Antioxidants are molecules that can neutralize free radicals.
**Why the Correct Answer is Right:** Vitamin C (ascorbic acid) is a potent antioxidant that prevents lipid peroxidation, protein oxidation, and DNA damage caused by free radicals. It protects the lens by neutralizing ROS and RNS, preventing oxidative stress-induced cellular damage.
**Why Each Wrong Option is Incorrect:**
A. Vitamin E (alpha-tocopherol) is an antioxidant that protects lipids, proteins, and DNA from oxidative damage. However, it does not directly protect the lens, making it an incorrect answer.
B. Glutathione peroxidase is an enzyme that reduces hydrogen peroxide to water and prevents lipid peroxidation. Although it plays a role in cellular protection, it doesn't directly protect the lens, rendering it an incorrect answer.
C. Superoxide dismutase (SOD) is an enzyme that converts superoxide radicals into hydrogen peroxide and oxygen, preventing lipid peroxidation and DNA damage. Although it is essential for cellular protection, it doesn't directly protect the lens, making it an incorrect answer.
D. Proline is a non-enzymatic antioxidant, a type of amino acid, that prevents lipid peroxidation and DNA damage. Although it plays a role in cellular protection, it doesn't directly protect the lens, making it an incorrect answer.
**Clinical Pearl:** The correct answer, Vitamin C, plays a vital role in preventing oxidative stress-induced cellular damage by neutralizing free radicals and protecting lens proteins, making it crucial for maintaining lens transparency and preventing cataract formation.
**Correct Answer:** D. Proline
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**Why Each Wrong Option is Incorrect:**
A. Vitamin E (alpha-tocopherol) is an antioxidant and prevents lipid peroxidation, but it doesn't directly protect the lens, making it an incorrect answer.
B. Glutathione peroxidase is an enzyme that reduces hydrogen peroxide to water and prevents lipid peroxidation. Although it is essential for cellular protection, it doesn't directly protect the lens, rendering it an incorrect answer.
C. Superoxide dismutase (SOD) is an enzyme that converts superoxide radicals into hydrogen peroxide and oxygen, preventing lipid peroxidation and DNA damage. Although it is essential for cellular protection, it doesn't directly protect the lens, making it an incorrect answer.
D. Proline is a non-enzymatic antioxidant, a type of amino acid, that prevents lipid peroxidation and DNA damage. Although it plays a role in cellular protection, it doesn't directly protect the lens, making it an incorrect answer.
**Clinical Pearl:** Lens antioxidants like Vitamin C, E, and GSH (Glutathione) directly protect the lens from oxidative damage by scavenging free radicals and preventing lipid peroxidation. In contrast, proline