Which of the following compounds directly inhibits the expression of the HMG-CoA reductase gene?
A) cholesterol
B) HMG-CoA
C) isopentenyl pyrophosphate
D) lanosterol
E) squalene

Question

Quizplus · Accepted Answer

Cholesterol directly inhibits the expression of the HMG-CoA reductase gene by acting as a feedback inhibitor, reducing the transcription of the gene to regulate cholesterol synthesis.  Regulation of HMG-CoA reductase (HMGR) activity is the primary means for controlling the level of cholesterol biosynthesis. This enzyme catalyzes the conversion of mevalonate to hydroxymethyl glutarylCoA. HMGR activity is controlled by 4 distinct mechanisms: feedback inhibition, control of gene expression, rate of enzyme degradation, and phosphorylationdephosphorylation. The first 3 control mechanisms are exerted by cholesterol itself. Cholesterol acts as a feedback inhibitor of preexisting HMGR as well as inducing rapid degradation of the enzyme. In addition, when cholesterol is in excess, the amount of mRNA for HMGR is reduced because of decreased expression of the gene.

Which of the Following Compounds Directly Inhibits the Expression of the HMG-CoA