24 Cholesterol Metabolism

Question 1

how does dietary cholesterol get absorbed into intestinal epithelial cells

Answer 1

by diffusion

Question 2

purposes of cholesterol

Answer 2

cholesterol is a major component of cellular membranes, precursor of bile salts and steroid hormones. plus, intermediates of cholesterol synthesis can make vitamin D, Coenzyme Q and dolichol

Question 3

the substrate and source of carbon for cholesterol

Answer 3

Acetyl CoA, which is derived from 3 sources , B oxidation of fatty acids, the pyruvate dehydrogenase pathway and the oxidation of ketogenic amino acids in the mitochondrial matrix. all 27 carbons of cholesterol come from Acetyl CoA

Question 4

the rate limiting step of cholesterol synthesis

Answer 4

mevalonate synthesis, the reduction of HMG CoA to mevalonate, using the enzyme HMG CoA reductase, which is located in the ER membrane

Question 5

HMG CoA contains how many Acetyl CoA

Answer 5

It has 3 Acetyl CoAs

Question 6

what are the 4 main stages of cholesterol synthesis

Answer 6

1. formation of HMG CoA from 3 Acetyl CoA and the formation of mevalonate 2.conversion of mevalonate to activated isoprenes 3. condensation of 6 isoprenes to form squalene 4. conversion of squalene to 4 ring steroid