21. Plasma Lipoproteins

Question 1

What are lipoproteins?

Answer 1

Spherical, macromolecular complexes of lipids and specific proteins

Question 2

What are the functions of lipoproteins?

Answer 2

1. Transport lipids to and from tissue

2. Keep lipid components soluble for transport in the plasma

Question 3

What are the 4 types of lipoproteins?

Answer 3

Chylomicrons
HDLs
LDLs
VLDLs

Question 4

Describe lipoprotein structure

Answer 4

Amphipathic outer shell

Neutral lipid core containing triacylglycerols and cholesterol esters

Question 5

What are the functions of apolipoproteins?

Answer 5

1. Structural components
2. Ligands for cell-surface receptors
3. Coenzymes for lipid metabolism enzymes

Question 6

What do chylomicrons transport?

Answer 6

Dietary fats and fat soluble vitamins

Question 7

What do chylomicrons contain?

Answer 7

Cholesterol
Cholesterol esters
Fat soluble vitamins
TAGs

Question 8

Name the steps in chylomicron metabolism

Answer 8

1. Apolipoprotein synthesis
2. Lipid synthesis
3. Chylomicron assembly
4. Maturation
5. Utilisation of chylomicron TAGs by the tissues
6. Clearance of chylomicron remnants

Question 9

What is synthesised in the first step of chylomicron metabolism?

Answer 9

Apolipoprotein B-48

Rough endoplasmic reticulum

Question 10

What is synthesised in the second step of chylomicron metabolism?

Answer 10

TAGs, cholesterol, phospholipids

Smooth endoplasmic reticulum

Question 11

What happens during chylomicron assembly?

Answer 11

Apo B-48 protein is loaded with lipid
Moves into golgi apparatus
Chylomicrons are packaged into secretory vesicles and released into the lymphatic system

Question 12

What do chylomicrons receive additional apolipoproteins from?

Answer 12

HDL particles

Question 13

Which apolipoprotein activates lipoprotein lipase?

Answer 13

Apo C

Question 14

Which apolipoprotein is recognised by liver receptors?

Answer 14

Apo E

Question 15

What does lipoprotein lipase do?

Answer 15

Degrades TAGs within the chylomicron to release fatty acids and glycerol

Question 16

How are chylomicron remnants cleared?

Answer 16

Chylomicrons get smaller and more dense as TAGs are removed
Apo C lost back to HDL
Liver receptors recognise Apo E on remnants and clear them from circulation for breakdown

Question 17

What do VLDLs transport?

Answer 17

Endogenously synthesised TAGs

Question 18

What do LDLs transport?

Answer 18

Endogenously synthesised cholesterol

Question 19

What do HDLs transport?

Answer 19

Cholesterol from tissues to the liver

Question 20

Which is the major protein in VLDL synthesis?

Answer 20

Apo B-100

Question 21

How do VLDLs become LDLs?

Answer 21

Losing Apo C and E back to HDL

Exchange of lipids with HDL

Question 22

How is LDL metabolised?

Answer 22

Oxidised-LDLs can be taken up by macrophages with high levels of SR-A
Macrophages become engorged with Ox-LDL and form Foam cells
This is a key step in the formation of atherosclerotic plaque

Question 23

How are HDLs formed?

Answer 23

Addition of lipids to Apo A-1

Question 24

What are the functions of HDLs?

Answer 24

1. Reservoir of apolipoproteins
2. Accumulation of unesterified cholesterol
3. Esterification of cholesterol
4. Reverse cholesterol transport

Question 25

What are disorders of VLDL and chylomicrons known as?

Answer 25

Hypertriglyceridaemia

Excess circulating VLDL

Question 26

What are the three types of Hypercholesterolaemia?

Answer 26

Heterozygous familial
Apoprotein B-100 gene mutations
Polygenic

Question 27

What is Tangier disease?

Answer 27

Autosomal recessive disease involving the ABCA1 gene mutation
Low plasma HDL cholesterol concentration
Accumulation of cholesterol in tissues and arteries