Question

Which of the following statements regarding lipid metabolism are correct?

I. All of the atoms of cholesterol are derived from acetyl-SCoA

II. Carbon atoms one and two of acetyl-SCoA are not present in equal amounts in cholesterol

III. 3-HMG-SCoA is a precursor of both mevalonate and acetoacetate

IV. Squalene is cyclized to lanosterol by a series of concerted hydride and methyl shifts requiring O₂ and NADPH

a. I and II

b. III and IV

c. I, II, and III

d. I, III, IV

e. I, II, III, IV

Answer 1

e. is correct option.

• Carbon atoms of cholesterol are derived from acetyl co.A in three stage of synthetic process.
• Carbon atoms one and two of acetyl co.A are not present in equal amount in cholesterol due the presence of hydrogen bonds between them.
• 3HMG-SCoA is a precursor of both mevalonate and ketogenesis pathway. It is formed from acetyl Co A and acetoacetyl Co A by HMG Co A synthase.
• Cyclization of squalene -2,3-epoxide to lanosterol occur through a series of concentrated 1,2- methyl group and hydride shifts along the squalene chain. It require O2​​​​​​​ and NADPH.​​​​