Duan: Lipoprotein metabolism overview (TMI...)

Question 1

protein-lipid complexes responsible for transport of plasma lipids

Answer 1

lipoproteins

Question 2

What makes up the surface of lipoproteins? What makes up the core?

Answer 2

surface: phospholipids, unesterified cholesterol, Apolipoproteins (Apo)
core: cholesterol esters and TAGs

Question 3

Which lipoproteins have the greatest diameter and the greatest percentage of total lipids?

Answer 3

chylomicrons (greatest diameter, 99% lipid, 1% protein)

VLDL (large diameter, 92% lipid, 8% protein)

Question 4

Which lipoproteins have intermediate/small diameter and the greatest percentage of total protein?

Answer 4

LDL: 80% lipid, 20% protein
HDL: 50% lipid, 50% protein

Question 5

Recall the progression in diameter and density in the different lipoproteins

Answer 5

chylomicrons (largest, most lipids, least protein)
VLDL (large, mostly lipids, little protein)
LDL (small, mostly lipids, 20% protein)
HDL (smallest, 1/2 lipid, 1/2 protein)

Question 6

What are the two pathways for lipoprotein metabolism?

Answer 6

exogenous/chylomicron pathway (dietary fat)
endogenous pathway (lipids synthesized by the liver)

Question 7

Briefly discuss the exogenous pathway of lipoprotein metabolism

Answer 7

Bile emulsifies fat in the chyme of the stomach
Pancreatic lipase cleaves TAGs into 2 FA + 1 MAG
Enterocytes of gut absorb these molecules - inside the enterocytes, they reform into TAGs
Then the TAGs gain APOB-48 and become chylomicrons
Chylomicrons move through lymphatic system into the blood stream
In the blood, HDL donates APOCII and APOE to the chylomicron making it “mature”
Through APOCII, chylomicrons activate LPL on endothelial cells lining blood vessels
This converts the TAGs to glycerol and FAs which can cross into the tissues and be stored in adipose or muscle tissue
The rest of the chylomicron which has lost TGs (chylomicron remnant) continues circulating thru the blood until its APOC is gone.
Then it travels to the liver and thru its APOE receptor is endocytosed into the liver
In the liver, FA and glycerol can be stored for later use

Question 8

Briefly discuss the endogenous pathway for lipoprotein metabolism

Answer 8

In the liver hepatocytes, TAGsare assembled with CEs and APOB100 to form VLDL particles. These are released into the bloodstream.
They pick up APOCII and APOE from HDL in the blood. They are mature.
They encounter LPL on endothelial cells of vessels and are absorbed into peripheral tissues (adipose and muscle) and deliver TAG contents.
The remnant becomes an IDL and can return to the liver, where they can release more glycerol and FAs.
They become LDL
LDL circulates and releases lipids, like cholesterol in the body.

Question 9

What does HDL donate to circulating chylomicrons and VLDL?

Answer 9

APOCII
APOE
cholesterol esters

Question 10

This component of chylomicrons and VLDLs activates lipoprotein lipase and causes the hydrolysis of TGs into glycerol and FFAs

Answer 10

APOCII

Question 11

The primary carrier of cholesterol

Answer 11

LDL

Question 12

Component of VLDL, IDL, and LDL, which is positively correlated with cardiovascular disease

Answer 12

APOB100

Question 13

What happens when LDL binds to LDL receptors on hepatic tissues and extrahepatic tissues?

Answer 13

the LDL complex get endocytosed and releases free cholesterol into the cytoplasm, which can be used in membranes

Question 14

Transport cholesterol from peripheral tissues to liver

Answer 14

HDL