This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Biochemistry
Precursor of all steroid hormones - 
Select and explain. 
A. Pregnenolone, B. Deoxycortisol, C. Androstenedione, D. Dehydroepiandrosterone
A: Pregnenolone
Answer: A: Pregnenolone 
Explanation: Ans. is 'a' i.e., Pregnenolone o All steroid hormones originate from cholesterol.o Steps involved in biosynthesis of various steroid hormones are as follows :-Cholesterol is first acted upon by desmolase to form a 21-carbon product pregnenolone, which is the biosynthetic precursor of all steroid hormones.Pregnenolone is converted to progesterone by dehydrogenase.Progesterone is further converted to glucocorticoids and mineralcorticoids by hydroxy lotions. These reactions are affected by monooxygenases w'hich require cytochrome P-450 as an intermediate electrone carrier. These monooxygenases are -17-hydroxylase and 21-hydroxylase - Microsomal11-hydroxyalse - Mitochondrial