What common substrate is used in the biosynthesis of adrenal steroids, including androgens and estrogens?

• A. Cortisol
• B. Catecholamines
• C. Progesterone
• D. Cholesterol

Answer: (D)

Steroid hormones in the adrenal cortex all originate from cholesterol. Cholesterol is taken into mitochondria and cleaved to pregnenolone, then through a series of enzymatic steps is converted into the various adrenal steroids—glucocorticoids, mineralocorticoids, and adrenal androgens—with estrogens formed later by aromatization of androgens. Because this single molecule provides the four-ring structure needed for all these hormones, cholesterol is the common substrate for their biosynthesis. The other substances listed are either products of this pathway (like cortisol) or come from different biosynthetic routes (like catecholamines from tyrosine), not the universal starting material.