According to the two-cell theory of ovarian steroidogenesis, which enzyme is present only in granulosa cells and explains why these cells alone can convert theca-derived androgens into estrogens?
- A 17-alpha-hydroxylase
- B 3-beta-hydroxysteroid dehydrogenase
- C Aromatase (CYP19) ✓
- D Cholesterol desmolase
Correct answer: C. Aromatase (CYP19)
Explanation
Theca cells possess cholesterol desmolase and 17-hydroxylase/17,20-lyase activity, so they synthesize androstenedione and testosterone but lack aromatase. Granulosa cells express aromatase (CYP19), which converts these androgens to estradiol under FSH stimulation. This division of labour is the essence of the two-cell, two-gonadotrophin theory. Cholesterol desmolase and 17-alpha-hydroxylase are theca cell enzymes, so options A, B and D describe steps that occur before the substrate ever reaches the granulosa cell.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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