This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cholesterol and Lipoproteins, Subject name: Biochemistry
In cholesterol synthesis, which is rate limiting amino acid 
Select and explain. 
A. HMG CoA reductase, B. HMG CoA synthetase, C. 7 alpha hydroxylase, D. Phosphofructokinase
A: HMG CoA reductase
Answer: A: HMG CoA reductase 
Explanation: Ans. is 'a' i.e. HMG CoA reductase In cholesterol synthesis this step-HMG CoA - Mevalonate is the rate limiting step and HMG-CoA reductase is the rate limiting enzyme.HMG CoA synthetase is the rate limiting enzyme for ketone bodies synthesis* 7 alpha hydroxylase is for - Bile acid synthesis* Phosphofructokinase is for - Glycolysis*