L43-cholestrol Metabolism Flashcards
Where is cholesterol synthesized
By liver and extra-hepatic tissues and enters circulation as component of lipoproteins
Main food sources of dietary cholesterol
Egg yolk Shrimp Beef Poultry Cheese Butter
Imp of cholestrol
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
Describe the process of synthesis of cholesterol
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
Primary source of cholesterol
LDL
Where are all the carbon atoms in cholesterol provided
By acetyl coA from CAC and NADPH provides reducing equivalents
How is cholesterol synthesis regulated
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
Cholesterol degradation
Eliminated by body by conversion to bile acids and bile salts
Describe hypercholestrolemia
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