Antioxidants & Minerals MCQs

Peroxisomes (or) microbodies are concerned with three vital functions in a cell namely: Generation and degradation of hydrogen peroxide (H2O2) Oxidation of very long chain fatty acids (ag, C20 C22) Detoxification of harmful chemicals Reference: Ganong, 25th edition page no.38

Explanation: Erythrocuprein, also known as ceruloplasmin, is a copper-carrying protein in the blood. Each molecule of ceruloplasmin contains one atom of copper that is essential for its enzymatic activity, which includes oxidising iron and functioning in iron metabolism.

Chemical modification of the proteins or lipids in plasma low-density lipoprotein (LDL) leads to abnormal LDL. Option A & Option B: Such modified LDL is not recognized by the liver LDL receptors, and so is not cleared by the liver. Option C: Such modified LDL is highly atherogenic. Option D: The modified LDL is taken up by macrophage scavenger receptors. Lipid-engorged macrophages infiltrate under blood vessel endothelium (especially when there is already some damage to the endothelium), and are killed by the high content of unesterified cholesterol they have accumulated. This occurs in the development of atherosclerotic plaques. Reference: Harper's illustrated biochemistry 32nd edition CH 45 PN 542

In erythrocytes and other tissues, the enzyme glutathione peroxidase, containing selenium as a prosthetic group, catalyzes the destruction of H2O2 and lipid hydroperoxides through the conversion of reduced glutathione to its oxidized form, protecting membrane lipids and haemoglobin against oxidation by peroxides. So, Option C is correct. Reference: Harper's illustrated biochemistry 32nd edition CH 12 PN 114

In erythrocytes and other tissues, the enzyme glutathione peroxidase, containing selenium as a prosthetic group, catalyzes the destruction of H2O2 and lipid hydroperoxides through the conversion of reduced glutathione to its oxidized form, protecting membrane lipids and hemoglobin against oxidation by peroxides Selenium is present in various enzymes as part of the 21 st amino acid, Selenocysteine. Selenocysteine containing enzymes include: Glutathione Peroxidase (1-8) Iodothyronine Deiodinase (1-3) Thioredoxin reductase (1-3) Glucose-6-phosphate dehydrogenase Exportin-1 LRP-2, LRP-8 eIF-4A3 eEFsec Selenoprotein H, I, K, M, N, O, P, R (1,2,3), S, T, U, V, W Selenocysteine Lyase & Synthase Selenophosphate synthetase 1 & 2 Tocopherol alpha transfer proteins Reference: Harper's 32 nd edition, page 122

Explanation: Glutathione peroxidase (GPx) is a key antioxidant enzyme that reduces hydrogen peroxide and organic hydroperoxides to water and alcohols, respectively, using glutathione as a reducing agent. Selenium is an essential co-factor for this enzyme, as it is incorporated into its active site as the amino acid selenocysteine , which is critical for its catalytic activity. Explanation of other options: Manganese (Option A): Manganese is a co-factor for enzymes like manganese superoxide dismutase and arginase . Copper (Option C): Copper is a co-factor for copper-zinc superoxide dismutase and cytochrome c oxidase. Magnesium (Option D): Magnesium is a co-factor for many ATP-dependent enzymes like kinases and polymerases. Key Takeaways: Selenium is the crucial co-factor for the antioxidant enzyme glutathione peroxidase. A deficiency can impair the body's ability to neutralize peroxides.

Explanation: The enzyme glutathione peroxidase is an important antioxidant enzyme that helps protect cells from oxidative damage by reducing hydrogen peroxide and organic hydroperoxides. Zinc is a cofactor for many enzymes and plays a crucial role in cellular metabolism, immune function, and protein synthesis. It is also involved in the activity of several antioxidant enzymes, such as superoxide dismutase (SOD), which helps neutralize free radicals. However, it is not the primary cofactor for glutathione peroxidase.

Ans. is 'c' i.e., Deficiency of L-gulonolactone oxidase In man, other primates and guinea pigs, ascorbic acid can be synthesized due to absence of L-glucanolactone oxidase, an enzyme used in lower animals to synthesise ascorbic acid as a byproduct of uronic acid pathway (glucuronic acid cycle).