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Cholesterol as Precursor for Steroid Hormones Biology Exam Facts
Cholesterol is the key precursor steroid for testosterone, estrogen, and other hormones via enzymatic pathways from pregnenolone—not glycogen, insulin, or glycerol—essential biosynthesis knowledge for General Biology certification.
Question
From which of the following base steroids, do other steroids like testosterone and estrogen are formed?
A. Glycogen
B. Insulin
C. Glycerol
D. Cholesterol
Answer
D. Cholesterol
Explanation
Cholesterol serves as the foundational precursor steroid from which all other steroid hormones, including androgens like testosterone and estrogens like estradiol, are biosynthesized through enzymatic modifications in the gonads, adrenal glands, and placenta. This process begins with cholesterol’s four-ring cyclopentanoperhydrophenanthrene structure, which undergoes side-chain cleavage via cytochrome P450 enzymes (e.g., CYP11A1) to form pregnenolone, the universal starting point for steroidogenesis; subsequent hydroxylations, oxidations, and reductions—such as 17α-hydroxylation and aromatization—yield testosterone (in testes/Leydig cells) and its conversion to estrogen via aromatase in ovarian granulosa cells or adipose tissue. Glycogen (a glucose polysaccharide), insulin (a peptide hormone), and glycerol (a triacylglycerol component) play no role in steroid pathways, as steroids derive exclusively from the mevalonate-isoprenoid-cholesterol route rather than carbohydrate or protein metabolism.