Lipoproteins 1

Question 1

Answer 1

Question 2

Describe polarity of apolipoprotein.

Answer 2

They are amphipathic

Question 3

What are 3 things that apolipoproteins provide?

Answer 3

1) Structural stability
2) Mediate cellular uptake
3) regulate enzymes in lipid metabolism

Question 4

Density is _______ proportional to diameter

Answer 4

Inversely

Question 5

Answer 5

Question 6

What is HDLs role with respect to apolipoproteins?

Answer 6

HDL acts as a reservoir of apolipoproteins and it exchanges apolipoproteins with other lipoproteins .

Question 7

What function does ApoB serve?

Answer 7

Structural Apolipoprotein

Question 8

VLDL contain ApoB ###?

Chylomicrons contain ApoB###

Answer 8

100

48

Question 9

What is the relationship between ApoB100 and ApoB48

Answer 9

They are made from the same transcript. ApoB48 is 48% of ApoB100. Example of RNA editing that results in different gene product from same trasncript.

Question 10

Where are chylomicrons and VLDL metabolized?

Answer 10

In the vascular system b/c they are too large to diffuse out of the vasculature

Question 11

Apo_____ on Chylomicrons and VLDL is recognized by lipoprotein lipase in the membrane of endothelial cells.

Answer 11

C2

Question 12

Describe how chylomicrons and VLDL are metabolized.

Answer 12

Circulating –> lipoprotein lipase recognize ApoC2 on liporotein –> binding between ApoC2 and LPL –> LPL degrade lipoprotein and free FA diffuse into tissue and are used for energy or converted bak to TAGs for storage

Question 13

When Chylomicrons and VLDL are metabolized, the tissue does not take up all the contents of the lipoprotein. What is the name for the remaining lipoprotein?

Answer 13

Remnant

Question 14

Describe the process of forming a chylomicron remnant.

Answer 14

Chylomicron digested in circulation –> when LPL activity is done chylomicron transfers ApoC2 and ApoE back to HDL to become chylomicron remnant.

Question 15

Chylomicron remnants taken up by the _____

Answer 15

Liver

Question 16

_____ is the remnant formed from VLDL

In the formation of this remnant, what apolipoproteins are exchanged?

40-60% of this remnant is taken up by what organ?

Answer 16

IDL

VLDL returns ApoC2 and ApoE back to HDL

Liver

Question 17

What is the remnant formed from IDL?

Where does this remodeling of IDL occur?

What is this lipoprotein rich in?

What apolipoprotein exchanges happens?

Answer 17

LDL

Liver –> enzyme that acts on IDL is hepatic lipase

Cholesterol esters

IDL transfer ApoE to HDL to become LDL

Question 18

What 2 apolipoproteins are needed for chylomicron remnant to be recognized by the liver?

Answer 18

ApoB48 and ApoE

Question 19

What 2 apolipoproteins are needed on LDL in order for it to be taken up by peripheral cells?

Answer 19

ApoE

ApoB-100

Question 20

Why is IDL and LDL clearance from the plasma slower than VLDL?

Answer 20

Because it has lower amounts of ApoE, which is necessary for both lipoproteins to be recognized by their target tissues (Liver for IDL and peripheral tissues for LDL).

Question 21

What does the slow clearance of LDL allow it to achieve?

Answer 21

Escapes vasculature and is able to gain access to all tissues and lymphatics except brain (blood/brain barrier)

Question 22

What is the role of PCSK9?

Answer 22

It binds to the LDL receptor and stimultes the internalization and degradation of the receptor. The receptor is recycled to the plasma membrane by endosomes.

Question 23

If a person had deficient PCSK9, what would be the result on their blood levels?

What if they had too much PCSK9?

Answer 23

Low PCSK9 –> low LDL receptor recycling –> Hypocholesterolemia

Hypercholesterolemia

Question 24

How are antibodies used to interact with PCSK9 to treat hypercholesterolemia?

Answer 24

They bind to PCSK9 and block its activity –> similar to low levels of recycling –> reduces cholesterol in blood.

Question 25

What is reverse cholesterol transport?

Answer 25

The transport of cholesterol back to the liver from the periphery. This process is mediated by HDL.

Question 26

What effect does the reverse cholesterol transport system have on cholesterol synthesis?

Answer 26

Most of cholesterol is made in the liver. Cholesterol acts as inhibitor of its own production via regulation of HMGcoA reductase –> more cholesterol from periphery coming to liver reduces production of cholesterol by liver.

Question 27

What effect does reverse cholesterol transport have on LDL levels?

Answer 27

If levels of cholesterol in cells decreases b/c it is being sent back to the liver, those cells will upregulate expression of their LDL receptors to get more cholesterol into the cells. As such, LDL levels will decrease because the cells need more cholesterol.

Question 28

Describe the means by which HDL delivers cholesterol to peripheral cells via selective cholesterol uptake.

Answer 28

HDL delivers cholesterol to liver and steroidgenic tissues directly by binding to SR-BI receptor. This transfer is not dependent on internalization of receptor/lipoprotein compelx and subsequent internal degradation. HDL just releases cholesterol esters to cell and releases without changing HDL levels in blood.