This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Precursor of all steroid hormones ? 
Select and explain. 
A. Pregnenolone, B. Deoxycoisol, C. Androstenedi one, D. Dehydroepiandrosterone
A: Pregnenolone
Answer: A: Pregnenolone 
Explanation: All steroid hormones originate from cholesterol.Steps involved in biosynthesis of various steroid hormones are as follows :?i) Cholesterol is first acted upon by desmolase to form a 21-carbon product pregnenolone, which is the biosynthetic precursor of all steroid hormones.ii) Pregnenolone is conveed to progesterone by dehydrogenase.iii) Progesterone is fuher conveed to glucocoicoids and mineralcoicoids by hydroxylations. These reactions are affected by monooxygenases which require cytochrome P-450 as an intermediate electrone carrier. These monooxygenases are -a) 17-hydroxylase and 21-hydroxylase Microsomalb) 11-hydroxyalse --> Mitochondrial