L43-cholestrol Metabolism

Question 1

Where is cholesterol synthesized

Answer 1

By liver and extra-hepatic tissues and enters circulation as component of lipoproteins

Question 2

Main food sources of dietary cholesterol

Answer 2

Egg yolk
Shrimp
Beef
Poultry 
Cheese
Butter

Question 3

Imp of cholestrol

Answer 3

1-For synthesis of bile salts that are important in lipid digestion and absorption
2-For the synthesis of steroid hormones that are biologically important like sex hormones estrogen and progesterone
3-For the synthesis of vitamin D3
4-As a structure and material in biological membranes
5-As a component of Lipo proteins transport forms of lipid based energy

Question 4

Describe the process of synthesis of cholesterol

Answer 4

Two acetyl coa molecules combine by thiolase forming acetoactylcoA
HMG coA synthase turns it in to HMG CoA
HMG coA reductase turns it in to mevalonate obtaining hydrogens from NADPH

Question 5

Primary source of cholesterol

Answer 5

LDL

Question 6

Where are all the carbon atoms in cholesterol provided

Answer 6

By acetyl coA from CAC and NADPH provides reducing equivalents

Question 7

How is cholesterol synthesis regulated

Answer 7

Allosteric regulation:
dietary cholesterol inactivates HMG-coA reductase
Hormonal regulation:
Insulin activates by dephosphorylation
Glucagon inhibits by phosphorylation
Long term: drugs used to inhibit HMG-coA reductase as statins

Question 8

Cholesterol degradation

Answer 8

Eliminated by body by conversion to bile acids and bile salts

Question 9

Describe hypercholestrolemia

Answer 9

Term used for high blood cholesterol level
Leads to atherosclerosis inc risk for myocardial infarction and strokes
Can get deposited under skin and cause xanthomas
Can be due to genetic disorders where regulatory coA reductase is not sensitive to feedback inhibition or cholesterol receptors are defective This is known as familial hypercholesterolemia