Lecture 22: Cholerstrol synthesis and Lipoproteins

what is the structure of Cholestrol

4 fused rings

hydrocarbon tail

OH group

cholestrol is _____ with a polar head and a nonpolar body

ampipathic

cholestrol is derived from _____

Acetyl-coa

In the first stage of cholestrol synthesis, three acetate (in the form of acetly coA) condenswe to form _______

mevalonate

what is the name of the enzyme that forms mevalonate

HMG-CoA Reductase

in the second stage of cholestrol synthesis, mevalonate converts to phosphorylated ___ _____

5C isoprene

in the third stage of cholestrol synthesis, 6 isoprenes polymerize to form the ____ ____ _____

30 C linear squalene

in the fourth stage of cholestrol synthesis, squalene cyclizes to form the 4 rings that are modified to produce _______

cholestrol

what is the rate limiting step of cholestrol synthesis

The reduction of HMG-CoA to mevalonate by HMG-CoA reductas

Which stage of cholesterol synthesis produces activated isoprenes?

Stage 2 — Mevalonate → isoprenes using ATP.

How many acetyl-CoA molecules are needed to make one cholesterol molecule?

18

What cofactors are required for cholesterol synthesis?

ATP, NADPH, and O₂.

Name three compounds derived from activated isoprenes.

Steroids, vitamin E/K, coenzyme Q (ubiquinone).

steroid hormones are oxidized derivatives of _____

cholestrol

What are the three main fates of cholesterol after synthesis?

Conversion to bile acids, steroid hormones, or cholesteryl esters.

Which cholesterol derivative acts as a detergent to emulsify fats?

Bile acids.

Which derivative regulates cholesterol synthesis through feedback inhibition?

Oxysterols.

what are the storage form of cholestrol

cholestrol ethers

what do cholestrol ethers do

make the cholestrol more hydrophobic, unable to enter membranes and stored in the liver

lipids are carried through the plasma in spherical particle called plasma ______

lipoproteins

which lipoproteins are the largest, and least dense

chylomicrons

Which lipoprotein carries dietary triglycerides from the intestine?

chylomicrons

what is the order of lipoproteins from least to most dense

chylomicrons

very low density lipoproteins (VLDL)

low density lipoprotein (LDL)

high density lipoprotein (HDL)

which lipoprotein is the smallest and most dense

high density lipoprotein (HDL)

What lipoprotein delivers endogenous triglycerides from the liver to tissues?

VLDL

What is the main cholesterol delivery lipoprotein?

LDL

Which lipoprotein is responsible for reverse cholesterol transport?

HDL

- picks up cholestrol from cells and returns them to the liver

What enzyme in HDL converts cholesterol into cholesteryl esters?

Lecithin-cholesterol acyl transferase (LCAT).

what is the first stage in the lipoprotein pathway

chylomicrons deliver dietary fat to tissues

what happens after chylomicrons deliver dietary fat to the tissues

VLDL delivers endogenous fat from the liver to the tissues and becomes LDL

what happens after VLDL becomes LDL

LDL delivers cholestrol from the liver to the tissues

what happens after LDL delivers cholestrol from the liver to the tissues

HDL returns cholestrol from cells to liver