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1.5 Vitamin D & Retinoid Synthesis — Test 1
Q1. The biologically active form of vitamin D is:✓ 1,25-dihydroxycholecalciferol (calcitriol)
Q2. In the skin, vitamin D3 (cholecalciferol) is produced from 7-dehydrocholesterol by the action of:✓ Ultraviolet light
Q3. The first hydroxylation of vitamin D (at position 25) occurs in the:✓ Liver
Q4. The second hydroxylation that produces active 1,25-DHC occurs in the kidney and is catalysed by:✓ 1alpha-hydroxylase
Q5. Renal 1alpha-hydroxylase activity is increased by all of the following EXCEPT:✓ High serum phosphate
Q6. Which condition decreases conversion of 25-hydroxycholecalciferol to 1,25-dihydroxycholecalciferol?✓ Chronic renal failure
Q7. Vitamin D is classified as a hormone (rather than a mere vitamin) because it:✓ Is made in the body and acts via intracellular (nuclear) receptors
Q8. 1,25-Dihydroxycholecalciferol increases intestinal calcium absorption mainly by inducing the synthesis of:✓ Calbindin (a Ca2+-binding protein)
Q9. In vitamin D deficiency, the bone disease seen in children is:✓ Rickets
Q10. Retinoids are produced in the body from dietary vitamin A; the major dietary provitamin is:✓ beta-carotene
Q11. Among the retinoids, which form is produced by oxidation of retinal and CANNOT be reduced back?✓ Retinoic acid
Q12. The retinoid that is the functional component of the visual cycle is:✓ Retinal
Q13. Retinoic acid influences growth, differentiation and maintenance of epithelial tissue by:✓ Activating genes via intracellular (nuclear) receptors
Q14. Match each vitamin-D metabolite/compound with its description and select the correct option.✓ A-iii, B-ii, C-i
Q15. Both 1,25-dihydroxycholecalciferol and retinoic acid resemble steroid and thyroid hormones because they:✓ Cross the cell membrane and bind intracellular receptors that act as transcription factors
Q16. Which vitamin is considered to function as a hormone?✓ Vitamin D
Q17. Cholecalciferol, 25-hydroxycholecalciferol and 24,25-dihydroxycholecalciferol are best described as:✓ Inactive precursors/metabolites; only 1,25-DHC is active
Q18. The renal enzyme catalysing the activation step of vitamin D is also known as:✓ CYP27B1
Q19. During pregnancy and lactation, calcium for the fetus/milk is supplied partly from maternal bone. The vitamin-D-dependent process that increases dietary calcium uptake is:✓ Intestinal Ca2+ absorption via calbindin induction
Q20. 7-Dehydrocholesterol, the cutaneous precursor of vitamin D3, is itself a precursor of:✓ Cholesterol