Conversion of cholesterol into steroid hormones MCQs With Answer is an essential topic for B.Pharm students studying steroidogenesis, enzymology, and endocrine pharmacology. This introduction covers key concepts such as cholesterol transport, the rate-limiting side-chain cleavage to pregnenolone by CYP11A1, mitochondrial involvement, regulatory proteins like StAR, and downstream enzymes (3β-HSD, CYP17, CYP21A2, CYP11B1, aromatase). Understanding zones of the adrenal cortex, hormonal regulation by ACTH/LH/FSH, cofactors, and clinical implications like congenital adrenal hyperplasia and pharmacologic inhibitors is crucial. The following focused, exam-style MCQs reinforce biochemical pathways, enzyme defects, regulation, and therapeutic connections. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which enzyme catalyzes the conversion of cholesterol to pregnenolone, initiating steroidogenesis?
- 3β-Hydroxysteroid dehydrogenase
- CYP11A1 (side-chain cleavage enzyme)
- Aromatase (CYP19)
- HMG-CoA reductase
Correct Answer: CYP11A1 (side-chain cleavage enzyme)
Q2. Where does the conversion of cholesterol to pregnenolone primarily occur within the cell?
- Endoplasmic reticulum
- Golgi apparatus
- Mitochondrial inner membrane
- Peroxisome
Correct Answer: Mitochondrial inner membrane
Q3. Which protein facilitates the rate-limiting transfer of cholesterol into mitochondria for steroidogenesis?
- Apolipoprotein B
- Steroidogenic acute regulatory protein (StAR)
- Cholesteryl ester transfer protein (CETP)
- LDL receptor
Correct Answer: Steroidogenic acute regulatory protein (StAR)
Q4. Which cofactor is essential for cytochrome P450 enzymes involved in steroid biosynthesis?
- ATP
- NADH
- NADPH
- FADH2
Correct Answer: NADPH
Q5. Which enzyme converts pregnenolone to progesterone?
- 3β-Hydroxysteroid dehydrogenase (3β-HSD)
- 17β-Hydroxysteroid dehydrogenase
- 21-hydroxylase
- CYP19 (aromatase)
Correct Answer: 3β-Hydroxysteroid dehydrogenase (3β-HSD)
Q6. Which enzyme is responsible for 17α-hydroxylation and 17,20-lyase activity in steroidogenesis?
- CYP21A2 (21-hydroxylase)
- CYP11B1 (11β-hydroxylase)
- CYP17A1 (17α-hydroxylase/17,20-lyase)
- CYP19 (aromatase)
Correct Answer: CYP17A1 (17α-hydroxylase/17,20-lyase)
Q7. In the adrenal cortex, which zone primarily synthesizes aldosterone?
- Zona fasciculata
- Zona glomerulosa
- Zona reticularis
- Medulla
Correct Answer: Zona glomerulosa
Q8. Which hormone is the main regulator of adrenal cortisol synthesis?
- Luteinizing hormone (LH)
- Adrenocorticotropic hormone (ACTH)
- Atrial natriuretic peptide (ANP)
- Thyroid-stimulating hormone (TSH)
Correct Answer: Adrenocorticotropic hormone (ACTH)
Q9. Aromatase (CYP19) converts which substrates into estrogens?
- Cholesterol directly into estradiol
- Progesterone into estrone
- Androgens (e.g., androstenedione, testosterone) into estrogens
- Cortisol into cortisone
Correct Answer: Androgens (e.g., androstenedione, testosterone) into estrogens
Q10. Which enzyme deficiency is most commonly associated with congenital adrenal hyperplasia (CAH)?
- 11β-Hydroxylase deficiency
- 21-Hydroxylase deficiency
- 17α-Hydroxylase deficiency
- Aromatase deficiency
Correct Answer: 21-Hydroxylase deficiency
Q11. Which electron carrier system transfers electrons to mitochondrial P450 enzymes during steroidogenesis?
- Cytochrome P450 reductase directly from cytosol
- Adrenodoxin reductase and adrenodoxin (ferredoxin)
- NADH dehydrogenase complex I
- Glutathione peroxidase system
Correct Answer: Adrenodoxin reductase and adrenodoxin (ferredoxin)
Q12. Which steroid is the immediate product of CYP11A1 activity on cholesterol?
- Progesterone
- Pregnenolone
- Deoxycortisol
- Androstenedione
Correct Answer: Pregnenolone
Q13. Which enzyme converts 17α-hydroxypregnenolone to dehydroepiandrosterone (DHEA)?
- 3β-HSD
- 17,20-lyase activity of CYP17
- 21-hydroxylase
- Aromatase
Correct Answer: 17,20-lyase activity of CYP17
Q14. Which protein transports cholesterol in the blood to steroidogenic tissues?
- Cholesterol esterase
- Low-density lipoprotein (LDL)
- Albumin only
- Collagen
Correct Answer: Low-density lipoprotein (LDL)
Q15. Which enzyme converts 11-deoxycortisol to cortisol?
- CYP21A2 (21-hydroxylase)
- CYP11B1 (11β-hydroxylase)
- 3β-HSD
- 17β-HSD
Correct Answer: CYP11B1 (11β-hydroxylase)
Q16. What is the main storage form of cholesterol in steroidogenic cells?
- Free cholesterol in membrane bilayers
- Cholesteryl esters in lipid droplets
- Phospholipids in ER
- Sphingomyelin vesicles
Correct Answer: Cholesteryl esters in lipid droplets
Q17. Which enzyme converts androstenedione to testosterone?
- 17β-Hydroxysteroid dehydrogenase (17β-HSD)
- 3β-HSD
- Aromatase
- CYP21A2
Correct Answer: 17β-Hydroxysteroid dehydrogenase (17β-HSD)
Q18. Which adrenal zone primarily produces cortisol?
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
- Medulla
Correct Answer: Zona fasciculata
Q19. Which hormone stimulates aldosterone secretion from the zona glomerulosa?
- ACTH only
- Angiotensin II
- Prolactin
- Calcitonin
Correct Answer: Angiotensin II
Q20. In steroidogenesis, which step is considered the rate-limiting step?
- Conversion of progesterone to deoxycorticosterone
- Uptake of LDL by receptor-mediated endocytosis
- Transport of cholesterol into mitochondria and side-chain cleavage
- Aromatization of androgens to estrogens
Correct Answer: Transport of cholesterol into mitochondria and side-chain cleavage
Q21. Which enzyme deficiency leads to accumulation of 17-hydroxyprogesterone and androgen excess?
- 21-Hydroxylase deficiency
- 11β-Hydroxylase deficiency
- 17α-Hydroxylase deficiency
- Aromatase deficiency
Correct Answer: 21-Hydroxylase deficiency
Q22. Which protein carries most circulating cortisol in blood?
- Sex hormone-binding globulin (SHBG)
- Albumin only
- Corticosteroid-binding globulin (CBG)
- Transferrin
Correct Answer: Corticosteroid-binding globulin (CBG)
Q23. Which enzyme converts progesterone to 11-deoxycorticosterone in the mineralocorticoid pathway?
- 21-Hydroxylase (CYP21A2)
- 11β-Hydroxylase (CYP11B1)
- CYP17A1
- 3β-HSD
Correct Answer: 21-Hydroxylase (CYP21A2)
Q24. Which of the following is a direct precursor of aldosterone?
- Cortisol
- 11-Deoxycorticosterone (DOC)
- Testosterone
- Estradiol
Correct Answer: 11-Deoxycorticosterone (DOC)
Q25. In peripheral tissues, which enzyme converts estrone to estradiol?
- Aromatase (CYP19)
- 17β-Hydroxysteroid dehydrogenase (17β-HSD)
- 3β-HSD
- 11β-HSD
Correct Answer: 17β-Hydroxysteroid dehydrogenase (17β-HSD)
Q26. Which drug inhibits aromatase and is used to block estrogen synthesis?
- Ketoconazole
- Letrozole
- Spironolactone
- Metyrapone
Correct Answer: Letrozole
Q27. Which enzyme is inhibited by metyrapone in cortisol synthesis tests?
- 11β-Hydroxylase (CYP11B1)
- 21-Hydroxylase (CYP21A2)
- Aromatase (CYP19)
- HMG-CoA reductase
Correct Answer: 11β-Hydroxylase (CYP11B1)
Q28. Which enzyme converts testosterone to estradiol in granulosa cells of the ovary?
- CYP17A1
- Aromatase (CYP19)
- 3β-HSD
- CYP11A1
Correct Answer: Aromatase (CYP19)
Q29. Which adrenal enzyme deficiency causes hypertension due to accumulation of 11-deoxycortisol or DOC?
- 21-Hydroxylase deficiency
- 11β-Hydroxylase deficiency
- 17α-Hydroxylase deficiency
- Aromatase deficiency
Correct Answer: 11β-Hydroxylase deficiency
Q30. Which enzyme reduces cortisone to active cortisol in peripheral tissues?
- 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1)
- 11β-Hydroxysteroid dehydrogenase type 2 (11β-HSD2)
- 3β-HSD
- 17β-HSD
Correct Answer: 11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1)
Q31. Which pathway yields androgens from cholesterol?
- Cholesterol → pregnenolone → progesterone → DOC → aldosterone
- Cholesterol → pregnenolone → 17α-hydroxypregnenolone → DHEA → androstenedione
- Cholesterol → squalene → lanosterol → cortisol
- Cholesterol → bile acids → testosterone
Correct Answer: Cholesterol → pregnenolone → 17α-hydroxypregnenolone → DHEA → androstenedione
Q32. Which molecule supplies electrons to mitochondrial CYP11A1 during cholesterol side-chain cleavage?
- NADH via complex I
- Adrenodoxin (ferredoxin) after reduction by adrenodoxin reductase
- Cytochrome c
- Glutathione
Correct Answer: Adrenodoxin (ferredoxin) after reduction by adrenodoxin reductase
Q33. Which of the following is NOT a source of cholesterol for steroidogenesis?
- De novo synthesis via HMG-CoA reductase
- LDL receptor-mediated uptake
- Hydrolysis of cholesteryl esters from lipid droplets
- Conversion of bile acids back to cholesterol
Correct Answer: Conversion of bile acids back to cholesterol
Q34. Which enzyme converts 17α-hydroxyprogesterone to 11-deoxycortisol?
- 17,20-lyase
- 21-Hydroxylase (CYP21A2)
- Aromatase (CYP19)
- 3β-HSD
Correct Answer: 21-Hydroxylase (CYP21A2)
Q35. Which process is critical for acute stimulation of steroid hormone synthesis?
- Increased expression of LDL receptor only
- Rapid upregulation and activity of StAR protein
- Immediate activation of aromatase
- Activation of HMG-CoA reductase
Correct Answer: Rapid upregulation and activity of StAR protein
Q36. Which enzyme is primarily responsible for converting DHEA to androstenedione?
- 17β-HSD
- 3β-HSD
- Aromatase
- 21-Hydroxylase
Correct Answer: 3β-HSD
Q37. Which change is expected in classic 21-hydroxylase deficiency?
- Decreased androgens and salt wasting
- Decreased androgens and hypertension
- Increased androgens and salt wasting
- Increased estrogens and hypertension
Correct Answer: Increased androgens and salt wasting
Q38. Which enzyme activity is targeted by ketoconazole to suppress steroidogenesis?
- Aromatase only
- Multiple CYP enzymes including CYP17 and CYP11A1
- 3β-HSD exclusively
- HMG-CoA reductase
Correct Answer: Multiple CYP enzymes including CYP17 and CYP11A1
Q39. Where is aromatase primarily expressed for estrogen synthesis in females?
- Adrenal medulla only
- Placenta, granulosa cells, adipose tissue
- Zona glomerulosa exclusively
- Pancreas
Correct Answer: Placenta, granulosa cells, adipose tissue
Q40. Which steroid-binding protein carries most testosterone in men?
- Corticosteroid-binding globulin (CBG)
- Sex hormone-binding globulin (SHBG)
- Transferrin
- Albumin only
Correct Answer: Sex hormone-binding globulin (SHBG)
Q41. Which enzyme converts deoxycorticosterone to corticosterone in the adrenal cortex?
- CYP11B2 (aldosterone synthase)
- CYP17A1
- Aromatase
- 3β-HSD
Correct Answer: CYP11B2 (aldosterone synthase)
Q42. Which adrenal enzyme has both 11β-hydroxylase and aldosterone synthase activities in humans?
- CYP11A1
- CYP11B1 and CYP11B2 are distinct but related enzymes
- CYP17A1
- Aromatase (CYP19)
Correct Answer: CYP11B1 and CYP11B2 are distinct but related enzymes
Q43. Which lipid droplet enzyme mobilizes cholesteryl esters to free cholesterol for steroidogenesis?
- Hormone-sensitive lipase (HSL)
- HMG-CoA reductase
- Lecithin–cholesterol acyltransferase (LCAT)
- ACAT (acyl-CoA:cholesterol acyltransferase)
Correct Answer: Hormone-sensitive lipase (HSL)
Q44. Which deficiency would reduce sex steroid (androgen/estrogen) production but spare mineralocorticoid synthesis?
- 21-Hydroxylase deficiency
- 17α-Hydroxylase deficiency
- 11β-Hydroxylase deficiency
- CYP11A1 deficiency
Correct Answer: 17α-Hydroxylase deficiency
Q45. Which clinical test assesses peripheral aromatase activity or estrogen production?
- ACTH stimulation test
- Measurement of plasma estrone/androstenedione ratio
- Oral glucose tolerance test
- Thyroid function test
Correct Answer: Measurement of plasma estrone/androstenedione ratio
Q46. Which enzyme catalyzes the conversion of cholesterol to bile acids, separate from steroid hormone synthesis?
- CYP7A1 (cholesterol 7α-hydroxylase)
- CYP11A1
- CYP17A1
- Aromatase
Correct Answer: CYP7A1 (cholesterol 7α-hydroxylase)
Q47. Which factor increases transcription of steroidogenic enzymes in the adrenal cortex chronically?
- Acute sympathetic stimulation
- Chronic elevation of ACTH
- Increased insulin only
- Decreased angiotensin II
Correct Answer: Chronic elevation of ACTH
Q48. Which enzyme interconverts active cortisol and inactive cortisone in the kidney to protect mineralocorticoid receptors?
- 11β-HSD2
- 11β-HSD1
- 3β-HSD
- 17β-HSD
Correct Answer: 11β-HSD2
Q49. In steroid biosynthesis, what is the role of HMG-CoA reductase relative to cholesterol availability?
- Directly converts cholesterol to pregnenolone
- Rate-limiting enzyme for de novo cholesterol synthesis supplying substrate for steroidogenesis
- Degrades cholesterol esters
- Transports cholesterol into mitochondria
Correct Answer: Rate-limiting enzyme for de novo cholesterol synthesis supplying substrate for steroidogenesis
Q50. Which pharmacologic agent blocks StAR function or expression and thereby reduces steroid hormone synthesis acutely?
- Fludrocortisone
- ACTH analog
- There are no widely used direct StAR inhibitors clinically; StAR dysfunction is primarily genetic
- Letrozole
Correct Answer: There are no widely used direct StAR inhibitors clinically; StAR dysfunction is primarily genetic
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