MEH: Lipid Transport

Question 1

What feature of lipids make them difficult to transport in the blood?

Answer 1

They’re insoluble in water

Question 2

How are fatty acids transported in the blood?

Answer 2

Bound to albumin

Question 3

How are the majority of lipids transported in the blood?

Answer 3

Lipoprotein particles

Question 4

Where does the body get the majority of its cholesterol from?

Answer 4

Some is obtained form the diet, but the majority is synthesised by the liver.

Question 5

Name 2 classes of molecules that cholesterol is the precursor for.

Answer 5

1. Bale acids

2. Steroid hormones (e.g. cortisol, aldosterone, testosterone, oestrogen)

Question 6

How is cholesterol transported around the body?

Answer 6

In the form of cholesterol esters (cholesterol with fatty acid chains)

Question 7

Describe the structure of a lipoprotein.

Answer 7

• Peripheral and integral apolioproteins
• Phospholipid monolayer
• Cargo (consisting of triacylglyerol, cholesterol ester, ADEK vits)

Question 8

Name 5 different lipoproteins.

Answer 8

1. Chylomicrons
2. VLDL
3. IDL
4. LDL
5. HDL

Question 9

Name the 2 lipoproteins involved in carrying fat.

Answer 9

• Chylomicrons

- VLDL

Question 10

Name the 2 lipoproteins involved in carrying cholesterol esters.

Answer 10

• IDL
• LDL
• HDL

Question 11

Put the 5 main lipoproteins in order of size. (Largest to smallest)

Answer 11

1. Chylomicron
2. VLDL
3. IDL
4. LDL
5. HDL

Question 12

Describe the 2 main roles of apolipoproteins.

Answer 12

1. Structural: packing of water insoluble lipid

2. Functional: Co-factor for enzymes and ligand surface receptors

Question 13

What apolipoproteins are found on VLDL, IDL, LDL?

Answer 13

apoB

Question 14

What apolipoproteins are found on HDL?

Answer 14

apoAI

Question 15

What apolipoproteins are found on chylomicrons?

Answer 15

apoB-48

apoC and apoE (once in the blood)

Question 16

Explain how tissues obtain the lipids they require from

lipoproteins.

Answer 16

• apoC binds to LPL (lipoprotein lipase) on adipocytes and muscle
• This releases fatty acids
• When triglyceride is reduced to ~20%, apoC dissociates and the chylomicron becomes a chylomicron remnant

Question 17

What happens to chylomicron remnants?

Answer 17

They return to the liver where the LDL receptor on hepatocytes bind apo E and it is taken up by receptor mediated endocytosis.

Question 18

What structural feature of LDL means they aren’t efficiently cleared by the liver?

Answer 18

They don’t have apoC or apoE

The liver LDL-Receptor has a high affinity for apoE

Question 19

Explain how disturbances to the transport of lipids can lead to
clinical problems.

Answer 19

• The half life of LDL is much longer than VLDL or IDL
• This means it is more susceptible to oxidative damage
• This can be taken up by macrophages that transform into foam cells
• These contribute to formation of atherosclerotic plaques

Question 20

What is the function of HDL?

Answer 20

Empty vessels to transport excess cholesterol from peripheral cells back to the liver for metabolism.

Question 21

Explain how hyperlipoproteinaemias may be treated.

Answer 21

• Diet (however most of cholesterol is synthesised by the body so this doesn’t help much)
• Lifestyle (increase exercise, stop smoking)
• Statins (inhibit HMG-CoA reductase)
• Bile salt sequestrants (cholesterol is the precursors to this)

Question 22

How does a patient with hyperlipoproteinaemia present.

Answer 22

• Yellow patches on the eyelid (Xanthelesma)
• Nodules on tendon (Tendon Xanthoma)
• Corneal Arcus

Question 23

What is the cause of type I, IIa and III type hyperlipoproteinaemias?

Answer 23

I: defective lipoprotein lipase causes chylomicrons in fasting plamsa.
IIa: Defective LDL receptor (Associated with CVD)
III: Defective apoE (Associated with CVD)