<prompt> The rate-limiting step in the synthesis of cortisol is catalyzed by:21-Hydroxylase3b-Hydroxysteroid dehydrogenaseCholesterol side-chain cleavage enzyme11b-Hydroxylase  <response>: Ans. C. Cholesterol side-chain cleavage enzymeThe first and rate-limiting step in all steroid biosynthesis is catalyzed by cholesterol sidechain cleavage enzyme, resulting in pregnenolone and iso caproic acid. 17a-hydroxylase, 3b-hydroxysteroid dehydrogenase, 21-hydroxylase, and 11b- hydroxylase are all involved in the synthesis of cortisol, but are not rate-limiting. 3-Hydroxy-3-methylglutaryl CoA reductase catalyzes the rate-limiting step in de novo cholesterol synthesis. 