Question

De novo fatty acid synthesis is primarily regulated by phosphorylation of acetyl-CoA carboxylase, which is stimulated by glucagon and/or epinepherine.

True

False

Which of these intermediates in cholesterol biosynthesis is the substrate for the enzyme at the key regulatory step of the pathway?

		dimethylallyl pyrophosphate
		beta-hydroxy-beta-methylglutaryl-CoA
		beta-isopentyl pyrophosphate
		mevalonate

Answer 1

Answer 1. True, Phosphorylation of acetyl-CoA carboxylase, which is stimulated by insulin, glucagon and epinepherine. Glucagon and epinephrine are resposible for inhibiting acetyl- CoA carboxylase to prevent synthesis of fatty acids. Insulin but acts exactly opposite to their function and activates carboxylase enzyme.

Answer 2.Correct answer is beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA). The key regulatory step in cholesterol biosynthesis is the conversion of beta-hydroxy-beta-methylglutaryl-CoA to mevalonate(HMG-CoA) by NADPH. Thus HMG-CoA is the required intermediate for the substrate for the enzyme during cholesterol synthesis.

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