Cholesterol

Question 1

What is mevalonate?

Answer 1

An intermediate in cholesterol synthesis

Question 2

What is the enzyme that catalyzes the reaction forming mevalonate?

Answer 2

Formed in a reaction catalyzed by HMG- CoA reductase

Question 3

What is the rate limiting enzyme in cholesterol biosynthesis?

Answer 3

HMG- CoA reductase

Question 4

What is squalene?

Answer 4

It is converted to lanosterol which is then converted to cholesterol

Question 5

What activates HMG- CoA reductase?

Answer 5

Insulin

Question 6

What inhibits HMG- CoA reductase?

Answer 6

AMP
Glucagon
High cholesterol levels

Question 7

How is HMG- CoA reductase regulated at the transcriptional level?

Answer 7

Inhibited by sterols like cholesterol

Question 8

How is HMG- CoA reductase regulated at the translational level?

Answer 8

Inhibited by non sterol metabolites derived from mevalonate

Question 9

How is HMG- CoA reductase regulated at the enzyme level?

Answer 9

Degradation is promoted by it s products, mevalonate and cholesterol

Question 10

How is HMG- CoA reductase regulated at the activity level?

Answer 10

Phosphorylation inhibits like via AMP and glucagon

Question 11

What is the rate limiting enzyme in bile acid synthesis?

Answer 11

7-α-hydroxylase

Question 12

What is the function of acyl-CoA cholesterol acyl-transferase (ACAT)?

Answer 12

Converts cholesterol to cholesterol ester

Question 13

What is the effect of increased levels of cholesterol on enzymes in the pathway?

Answer 13

• Inhibits HMG-CoA reductase (decreased cholesterol synthesis)
• Activates ACAT
  (increased cholesterol storage/utilization)
• Activates 7-a-hydroxylase
  (increased bile acid synthesis/utilization)

Question 14

What is the effect of decreased levels of cholesterol on enzymes in the pathway?

Answer 14

• Activates: HMG-CoA reductase (increased cholesterol synthesis)
• Inhibits: ACAT
  (decreased cholesterol storage/utilization)
• Inhibits: 7-a-hydroxylase
  (decreased bile acid synthesis/utilization)