Lipid Transport & Storage

Question 1

How are lipids transported?

Answer 1

Associated with a protein - 98% as lipoproteins and 2 % bound non-covalently to albumin

Question 2

Describe the structure of apoproteins

Answer 2

Involved in packaging non-water soluble lipids into a soluble form. Contain hydrophobic and hydrophilic regions.

Question 3

What are the main functions of apoproteins?

Answer 3

Activation of enzymes or recognition of cell surface receptors

Question 4

Describe the structure of a lipoprotein

Answer 4

Spherical, surface coat - phospholipids, cholesterol and apoproteins, hydrophobic core - TAGs and cholesterol esters

Question 5

What keeps lipoproteins stable?

Answer 5

Their shape which is dependent on the ratio of core to surface lipids

Question 6

What is the function of chylomicrons?

Answer 6

Transport dietary TAGs from intestines to tissues

Question 7

What is the function of VLDLs?

Answer 7

Transport of TAGs synthesis in liver to adipose for storage

Question 8

What is the function of LDLs?

Answer 8

Transport of cholesterol synthesised in liver to tissues

Question 9

What is the function of HDLs?

Answer 9

Transport of excess tissue cholesterol to liver for disposal (as bile salts)

Question 10

What happens to dietary TAGs?

Answer 10

Hydrolysed in the small intestine by pancreatic lipase. FAs enter epithelial cells - re-esterified to TAGs and then packaged into chylomicrons

Question 11

How are chylomicrons released into the blood?

Answer 11

Via the lymphatic system, from epithelial cells.

Question 12

Which tissues do chylomicrons affect?

Answer 12

Tissues that express the extracellular enzyme lipoprotein lipase

Question 13

What does lipoprotein lipase do?

Answer 13

Removes the core TAGs from lipoproteins. Hydrolyses TAGs in lipoproteins to give FAs and glycerol.

Question 14

Where can you find lipoprotein lipase?

Answer 14

Attached the inner surface of capillaries in muscles and adipose tissue

Question 15

What does lecithin:cholesterol acyltransferase (LCAT) do?

Answer 15

Restores stability of lipoproteins. Conversion of surface lipid to core lipid - cholesterol - cholesterol ester using FA derived from lecithin

Question 16

What happens if there is a deficiency in lecithin?

Answer 16

Unstable lipoproteins, general failure of lipid transport. Lipid deposits occur in many tissues and can lead to atherosclerosis

Question 17

How do tissues obtain cholesterol from LDLs?

Answer 17

Receptor-mediated endocytosis

Question 18

Outline the mechanism for the uptake of cholesterol

Answer 18

Cells synthesise LDL receptors, bind to specific apoproteins (Apo B100) on the LDL, endocytosis, lysosomal digestion, cholesterol esters - cholesterol

Question 19

What is hyperlipoproteinaemia?

Answer 19

Increased level of one or more of the plasma lipoproteins

Question 20

Describe type 1 hyperlipoproteinaemia

Answer 20

Chylomicrons present in fasting glucose, caused by defective lipoprotein lipase

Question 21

Describe type 2a hyperlipoproteinaemia

Answer 21

Raised LDL, associated with coronary artery disease that may be severe, unknown defect

Question 22

Describe type 2b hyperlipoproteinaemia

Answer 22

Raised LDL and VLDL, associated with coronary artery disease, unknown defect

Question 23

Describe type 3 hyperlipoproteinaemia

Answer 23

Raised LDL and chylomicrons remnants, associated with coronary artery disease, defective apoprotein (Apo E)

Question 24

Describe type 4 hyperlipoproteinaemia

Answer 24

Raised VLDL, associated with coronary artery disease, unknown defect

Question 25

Describe type 5 hyperlipoproteinaemia

Answer 25

Raised chylomicrons and VLDL in fasting plasma, associated with coronary artery disease, unknown defect

Question 26

What is familial hypercholesterolaemia?

Answer 26

Condition in which there may be an absence (homozygous) or deficiency (heterozygous) of functional LDL receptors.

Question 27

How can you diagnose hypercholesterolaemia?

Answer 27

Characterised by elevated levels of LDL and cholesterol in the plasma. Homozygotes - extensive atherosclerosis early

Question 28

How would you treat hyperlipoproteinaemias?

Answer 28

Diet and lifestyle modifications, drug therapy (statins)

Question 29

How does the liver dispose of cholesterol?

Answer 29

Converts it into bile. Bile salt sequestrants increase disposal from body - act by binding to bile salts in GIT, promoting their loss in faeces

Question 30

What are micelles?

Answer 30

Small assemblies of lipid molecules surrounded by polar molecules