Plasma Lipoproteins

Question 1

what is the function of lipoproteins?

Answer 1

functions

• to transport ipids to and from tissues
• to keep their lipid components soluble for transport in the plasma

Question 2

what is the most dense lipoprotein? Least dense?

Answer 2

most dense= HDL

least dense = chylomicrons

Question 3

there is a high concentration of cholesterol and cholesterol esters in which lipoprotein?

Answer 3

in the LDLs

Question 4

what is the function of apolipoproteins?

Answer 4

structural components and ligands for cell-surface receptors

• coenzymes for lipid metabolism enzymes

Question 5

what are the five major classes of apolipoproteins and their subclasses?

Answer 5

apolipoprotein A,B,C,D,E

Question 6

how are dietary lipids transported throughout the body?

Answer 6

by chylomicrons

Question 7

describe how Chylomicrons are made and destroyed?

Answer 7

1. apolipoprotein synthesis- in rough ER
2. lipid synthesis- of TG, cholesterol, phospholipids in smooth ER
3. chylomicron assembly in Golgi apparatus -
4. maturation - in blood plasma - given Apo C and E from HDLs
5. utilization of chylomicron TG by tissues- by activation of lipoprotein lipase (by Apo C/C2)
6. clearance of chylomicron remnants (no Apo C present anymore, but Apo E is exposed) - Apo E recognized by liver and remnants are sequentially destroyed

Question 8

what is the purpose of Apo C and Apo C2? How about Apo E ?

Answer 8

Apo C /C2 activate lipoprotein lipase in tissues and allow for extraction of TGs from the chylomicron

Apo E is recognized by liver receptors

Question 9

What is the purpose of VLDL, LDL and HDL in the body?

Answer 9

VLDL = transport endogenously synthesised TG

LDL= tranport endogenously synthesized cholesterol

HDL = transport cholesterol from tissues to liver

Question 10

Describe the synthesis and degradation of VLDLs

Answer 10

1. made in liver by process similar to chylomicrons
2. secreted into circulation - pick up ApoC/E from HDL
3. TG contained in VLDLs is degraded by Lipoprotein lipase
4. as TGs are removed, VLDL gets smaller and more dense- eventually becoming LDLs once they lose their ApoC/E

Question 11

what is the purpose of LDLs?

Answer 11

delivery of cholesterol to the peripheral tissues by receptor mediated endocytosis via LDL receptor

Question 12

what does the LDL receptor recognise?

Answer 12

it recognizes (Apo B-100) and (Apo E)

Question 13

what does the LDL receptor NOT recognize?

Answer 13

Apo B-48

Question 14

how do macrophages become foam cells?

Answer 14

they eat too many oxidised LDLs

Question 15

what can foam cells lead to?

Answer 15

atherosclerotic plaque

Question 16

how are HDLs synthesised?

Answer 16

they are formed in the blood by addition of lipids to apolipoprotein Apo A1 which is synthesised by liver and small intestine and develops into nascent HDL

Question 17

what is the function of HDL cells?

Answer 17

• reservoir of apolipoproteins C/E
• accumulating unesterified cholesterol
• rapid esterification of cholesterol
• reverse cholestrol transport - very important

Question 18

why does cholesterol need to be transported back to the liver?

Answer 18

for conversion to bile salts

excretion of bile

and use in steroid synthesis

Question 19

Hypertriglyceridaemia is a disorder of what?

Answer 19

of VLDL and chylomicrons

• lipoprotein lipase deficiency = lack of metabolism of TG
• apoprotein C2 deficiency = no activation of LPL

Question 20

hypercholesterolaemia is a disorder of what?

Answer 20

of LDLs

• lack of LDL receptor in heterozygous familial hypercholesterolaemia
• apoprotein B100 gene mutation - required for bindin gLDL to receptor
• polygenic hypercholesterolaemia - most high cholesterol cases

Question 21

Tangier disease is a disorder of what?

Answer 21

of HDLs

it is a mutation of the ABCA1 gene - leads to low plasma HDL cholesterol and accumulatio of cholesterol in tissues

Question 22

what is familial autosomal dominant HDL deficiecy?

Answer 22

ABCA1 gene mutation - leads to low HDL levels

Question 23

what is the most common patient group for hyperlipidaemia

Answer 23

polygenic - increased risk of CV disease due to high LDL levels and suppression of HDL by high TG levels