Lipid Metabolism: Cholesterol Synthesis

Question 1

What is the fate of cholesterol after synthesis?

Answer 1

Used in cell membranes

Converted into bile acids and secreted into small intestine through the bile duct

Converted to cholesteryl esters and either stored in intracellular lipid droplets or packed into lipoproteins and exported into circulatory system (Acyl-CoA cholesterol acyltransferase, ACAT)

Question 2

How does receptor mediated endocytosis of LDL work?

Answer 2

LDL receptors of liver, muscle, adipose tissue, macrophages that will recognize the ApoB-100.

ApoB-100 enables these cells (liver cells, etc.) to take up LDL particles via receptor-mediated endocytosis.

Once in the cell, receptors will be recycled and sent to plasma membrane while the LDL fuses with lysosome.

LDL needs to be degraded to release amino acids, fatty acids and cholesterol so the lysosome will degrade the ApoB-100 and cholesteryl esters.

Question 3

Where does LDL get made?

Answer 3

LDL made in ER and processed into plasma membrane through Golgi apparatus

Question 4

How does HDL particles reverse cholesterol transport?

Answer 4

ApoA-I on the surface of HDL activates lecithin-cholesterol acyltransferase (LCAT) in plasma

LCAT esterifies cholesterol in peripheral cell membranes with a fatty acid tail derived from phosphatidylcholine (lecithin)

The esterified cholesterol is taken up into HDL particles and can be returned to the liver

Question 5

What is LCAT?

Answer 5

lecithin-cholesterol acyltransferase

takes fatty acid and puts it with cholesterol to become cholesteryl ester