Day 6 - Biosynthesis of Cholesterol and Steroids

Can humans metabolize the sterol structure?

No

In the body, ____% of cholesterol is in the free form, ___% is esterified with long-chain FA --> cholesteryl esters

30

70

What are the major sources of liver cholesterol gain?

dietary cholesterol, chylomicron remnants, extrahepatic cholesterol, HDL, de novo synthesis

What are the major routes of liver cholesterol loss?

secretion of VLDL, free cholesterol in bile, conversion to bile

What is the rate-limiting enzyme for de novo cholesterol synthesis? (for sure know for test)

HMG-CoA reductase (1st step: making mevalonic acid)

Where do all of the 27 carbons of cholesterol come from?

Where does this occur?

acetyl-CoA

cytoplasm

What is the third step of cholesterol biosynthesis?

making squalene (involves condensation and reductive condensation)

What is the fourth step of cholesterol biosynthesis?

making cholesterol (squalene monooxygenase)

What are the two rate-limiting enzymes for de novo cholesterol biosynthesis?

What steps are they involved in?

Which one is more important?

HMG-CoA reductase: step 1 (making mevalonic acid), more important

Squalene monooxygenase: step 4 (making cholesterol), less important

What are the 3 crucial players of the cholesterol biosynthetic pathway?

- SREBP2

- HMG-CoA-reductase

- squalene monooxygenase

"don't need to know any more details on this slide" - Dr. Breakwell

What are the most abundant metabolic products of cholesterol?

bile acids

>95% of the bile salts are resorbed in the _______________ and returned to the _____________.

ileum

liver

What cholesterol is used to synthesize PRIMARY bile acids (cholic and chenodeoxycholic acid)?

Hepatic (liver)

Where are cholesterol and progesterone formed?

adrenal glands and gonads

Where are aldosterone and cortisol formed?

mostly in the adrenal glands

Where are testosterone and estradiol formed?

mostly in the gonads