s2m1 biochem – cholesterol metabolism

what’s the most important enzyme to start cholesterol synthesis?

what does it convert to what?

which drugs inhibit it?

how is it activated / inactivated?

what hormone stimulates activation?


converts Acetyl-CoA to Mevalonate

statins inhibit it

activated by dephosphorylasing by HMG-CoA reductase phosphorylase

inactivated by protein kinase that adds a phosphate

activated by insulin

what does SREBP (sterol regulatory element binding protein) do?

what acts as negative feedback for it?

it stimulates synthesis of the enzyme HMG-CoA reductase

cholesterol acts as negative feedback

what are the two Primary bile acids?

which enzyme is the rate limiting step for bile acid synthesis? what does the enzyme do?

Glycocholic acid ; Taurocholic acid


7;-hydroxylase (adds an OH group to cholesterol)

how is 7;-hydroxylase negatively regulated?

what hormone ; enzyme does it require for activation?

neg regulation by bile acids

requires thyroid hormones ; Vit C


how does the body get rid of excess cholesterol?

what’s the role of bile acids in this? (3 functions)

through feces

bile acids solubilize cholesterol preventing precipitation of it into gallbladder


they also act as emulsifying agents making dietary triacylglycerides accessible to pancreatic enzymes


they facilitate intestinal absorption of fat-soluble vitamins

what are the three symptoms of an obstructed bile duct?


pale (lack of bile) floating stools (high fat content)

Itching: bile in blood stream

jaundice: conjugated bilirubin 

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