Question

Outlines of cholesterol biosynthesis includes: A. 2 Acetyl CoA $\rightarrow$ Acetoacetyl CoA B. Mevalonate $\rightarrow$ HMG CoA C. Acetoacetyl CoA $\rightarrow$ HMG CoA D. Acetoacetyl CoA $\rightarrow$ 2 Acetyl CoA E. HMG CoA $\rightarrow$ Mevalonate Choose the correct answer from the options given below:

• A. A, B and C only \
• B. A and D only \
• C. A, C and E only \
• D. A, B and D only

Hint:

Acetyl-CoA $\rightarrow$ Acetoacetyl-CoA $\rightarrow$ HMG-CoA $\rightarrow$ Mevalonate. HMG-CoA Reductase is the key target blocked by statin drugs to lower blood cholesterol!

Answer 1

The Correct Option is C

Step 1: Concept Cholesterol synthesis is an intricate anabolic pathway occurring in the cytosol of eukaryotic cells, starting from basic 2-carbon acetyl units.

Step 2: Meaning The early stage of cholesterogenesis forms mevalonate, which acts as the committed 6-carbon building block for building isoprenoid units.

Step 3: Analysis Let us trace the initial sequential steps of the biosynthesis pathway: *
Step 1: Two molecules of acetyl-CoA condense via thiolase to yield Acetoacetyl-CoA $\rightarrow$ Statement A is a correct step. *
Step 2: Acetoacetyl-CoA condenses with a third acetyl-CoA via HMG-CoA synthase to form $\beta$-hydroxy-$\beta$-methylglutaryl-CoA (HMG-CoA) $\rightarrow$ Statement C is a correct step. *
Step 3: HMG-CoA is reduced by HMG-CoA reductase using $\text{NADPH}$ to form Mevalonate $\rightarrow$ Statement E is a correct step. Statements B and D describe inverted reactions that do not match the forward biosynthetic flux.

Step 4: Conclusion The correct set containing the valid forward biosynthetic reactions is A, C, and E. Final Answer: (C)