Carotenoids and Vitamins: chemistry and physiological significance MCQs With Answer

Introduction: Carotenoids and Vitamins: chemistry and physiological significance MCQs With Answer is designed for M.Pharm students to reinforce core concepts linking molecular structure to biological function. This set focuses on carotenoid chemistry — classification, biosynthesis, isomerization, and provitamin A activity — and on fat- and water-soluble vitamins: their chemical forms, metabolic activation, physiological roles, transport, deficiency signs, and toxicity. Questions probe mechanisms (e.g., antioxidant action, enzyme cofactors, nuclear receptor signaling), pharmacological uses of retinoids and vitamin derivatives, and factors affecting bioavailability. Each MCQ is targeted to develop conceptual depth and exam readiness for advanced pharmaceutical curricula.

Q1. Which structural feature distinguishes xanthophylls from carotenes?

• Presence of oxygen-containing functional groups
• Longer polyene chain length
• Saturated hydrocarbon backbone
• Branched isoprenoid units

Correct Answer: Presence of oxygen-containing functional groups

Q2. Beta-carotene acts as a provitamin A because it can be enzymatically cleaved to yield which product?

• Cholecalciferol (vitamin D3)
• Retinal (vitamin A aldehyde)
• Tocopherol (vitamin E)
• Ascorbic acid (vitamin C)

Correct Answer: Retinal (vitamin A aldehyde)

Q3. The principal enzyme responsible for central cleavage of beta-carotene into two molecules of retinal is:

• Beta-carotene 15,15′-monooxygenase (BCMO1)
• Carotene desaturase
• Carotenoid epoxidase
• Retinol dehydrogenase

Correct Answer: Beta-carotene 15,15′-monooxygenase (BCMO1)

Q4. Which statement best describes the antioxidant action of carotenoids in biological membranes?

• They donate electrons to regenerate glutathione directly
• They quench singlet oxygen and stabilize lipid peroxyl radicals
• They enzymatically decompose hydrogen peroxide
• They chelate free iron to prevent Fenton reactions

Correct Answer: They quench singlet oxygen and stabilize lipid peroxyl radicals

Q5. Which stereoisomeric form of carotenoids is generally more bioavailable and biologically active as provitamin A?

• All-cis isomers
• All-trans isomers
• Racemic mixtures
• Epoxy derivatives

Correct Answer: All-trans isomers

Q6. Which vitamin requires UVB radiation for its cutaneous synthesis from 7-dehydrocholesterol?

• Vitamin A
• Vitamin D3 (cholecalciferol)
• Vitamin E
• Vitamin K

Correct Answer: Vitamin D3 (cholecalciferol)

Q7. Which hepatic activation step converts cholecalciferol to the hormonally active form of vitamin D?

• 25-hydroxylation followed by 1α-hydroxylation in the kidney (to calcitriol)
• Direct epoxidation in the intestine to calcidiol
• Conversion to retinoic acid in the liver
• Methylation to form vitamin D2

Correct Answer: 25-hydroxylation followed by 1α-hydroxylation in the kidney (to calcitriol)

Q8. Which vitamin functions as an electron donor for prolyl and lysyl hydroxylases during collagen biosynthesis?

• Vitamin B12 (cobalamin)
• Vitamin C (ascorbic acid)
• Vitamin K (phylloquinone)
• Vitamin A (retinol)

Correct Answer: Vitamin C (ascorbic acid)

Q9. Tocopherols exert their primary biological action by which mechanism?

• Acting as coenzymes in carboxylation reactions
• Serving as lipid-soluble chain-breaking antioxidants in membranes
• Activating vitamin D receptor signaling
• Cleaving carotenoids to retinoids

Correct Answer: Serving as lipid-soluble chain-breaking antioxidants in membranes

Q10. Which biochemical consequence is most characteristic of vitamin K deficiency?

• Impaired gamma-carboxylation of glutamate residues in clotting factors leading to bleeding tendency
• Reduced formation of hydroxylated collagen and scurvy
• Excessive bone mineralization and hypercalcemia
• Neuropathy due to demyelination

Correct Answer: Impaired gamma-carboxylation of glutamate residues in clotting factors leading to bleeding tendency

Q11. Retinoic acid mediates many of vitamin A’s gene regulatory effects by binding to which nuclear receptors?

• RAR (retinoic acid receptor) and RXR (retinoid X receptor)
• VDR (vitamin D receptor) and PPAR (peroxisome proliferator-activated receptor)
• TLR (toll-like receptors)
• Estrogen receptor alpha and beta

Correct Answer: RAR (retinoic acid receptor) and RXR (retinoid X receptor)

Q12. Which factor decreases intestinal absorption of carotenoids from plant foods?

• Co-ingestion with dietary fat
• Food matrix: carotenoids tightly bound to protein or fiber
• Thermal processing that breaks cell walls
• Presence of bile salts and pancreatic lipase

Correct Answer: Food matrix: carotenoids tightly bound to protein or fiber

Q13. Hypervitaminosis A is most likely to produce which clinical finding?

• Night blindness amelioration
• Teratogenic effects and hepatotoxicity
• Hypocalcemia and rickets
• Hemorrhagic diathesis due to under-carboxylated clotting factors

Correct Answer: Teratogenic effects and hepatotoxicity

Q14. Which laboratory marker best reflects recent dietary intake of vitamin C?

• Serum ascorbic acid concentration
• Plasma retinyl esters
• Serum 25-hydroxyvitamin D
• Prothrombin time

Correct Answer: Serum ascorbic acid concentration

Q15. Which process explains why smoking lowers carotenoid and vitamin C status in the body?

• Increased oxidative stress leading to faster depletion of antioxidants
• Enhanced intestinal absorption of carotenoids
• Inhibition of hepatic metabolism of vitamins
• Upregulation of provitamin A conversion enzymes increasing retinol stores

Correct Answer: Increased oxidative stress leading to faster depletion of antioxidants

Q16. Which carotenoid is most potent as a provitamin A in humans?

• Alpha-carotene
• Beta-carotene
• Lutein
• Canthaxanthin

Correct Answer: Beta-carotene

Q17. The transport of newly absorbed fat-soluble vitamins and carotenoids from enterocytes to circulation primarily involves incorporation into:

• Chylomicrons
• High-density lipoproteins (HDL) only
• Albumin-bound monomers exclusively
• Direct portal vein transport without lipoproteins

Correct Answer: Chylomicrons

Q18. Which vitamin deficiency is classically associated with cheilosis, glossitis, and seborrheic dermatitis and also serves as a precursor for FAD and FMN?

• Vitamin B2 (riboflavin)
• Vitamin B12 (cobalamin)
• Vitamin K
• Vitamin A

Correct Answer: Vitamin B2 (riboflavin)

Q19. Which therapeutic retinoid is commonly used topically for acne and acts by normalizing keratinization and reducing comedone formation?

• Tretinoin (all-trans-retinoic acid)
• Calcitriol (1,25-dihydroxyvitamin D3)
• Isotretinoin (13-cis-retinoic acid) oral only, not topical
• Phytonadione (vitamin K1)

Correct Answer: Tretinoin (all-trans-retinoic acid)

Q20. Which statement best describes the metabolic interconversion among vitamin A forms in target tissues?

• Retinol is irreversibly converted to retinal and then to retinoic acid; retinoic acid cannot be reduced back to retinal
• Retinoic acid is the storage form transported in chylomicrons
• Retinol binds to cellular retinol-binding protein (CRBP) and can be reversibly oxidized to retinal for visual cycle or irreversibly oxidized to retinoic acid for gene regulation
• Retinal is converted to vitamin D in the kidney

Correct Answer: Retinol binds to cellular retinol-binding protein (CRBP) and can be reversibly oxidized to retinal for visual cycle or irreversibly oxidized to retinoic acid for gene regulation

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