Lipid Transport

Question 1

How are lipids transported in blood?

Answer 1

Lipids are insoluble in water. Approximately 2% of lipids are carried bound to albumin. Approximately 98% of lipids are carried as lipoprotein particles, consisting of phospholipid, cholesterol, cholesterol esters, proteins and TAG

Question 2

What is the range of total cholesterol found in the blood?

Answer 2

> 5.0 mmol/L is healthy

Question 3

Where is cholesterol obtained?

Answer 3

Some from diet but most synthesised in the liver (from acetyl-CoA)

Question 4

What are the 5 classes of lipoproteins?

Answer 4

• Chylomicrons (transport dietary fats)
• VLDL
• IDL
  -LDL
  -HDL

Question 5

What are the main carriers of TAGs

Answer 5

Chylomicrons and VLDL

Question 6

What are the main carriers of cholesterol esters?

Answer 6

IDL, LDL and HDL

Question 7

How do the size of lipoproteins change with density?

Answer 7

More dense particles are smaller in diameter
I.e. chylomicrons are the largest and HDL are the smallest

Question 8

What roles do apolipoproteins play in lipoproteins?

Answer 8

Structural: packaging water insoluble lipid
Functional: co-factor for enzymes, ligands for cell surface receptors

Question 9

What is the primary function of LDL?

Answer 9

To provide cholesterol from liver to peripheral tissues

Question 10

Why can’t the liver efficiently clear LDL?

Answer 10

LDL don’t have apoC or apoE
Liver LDL-receptor has high affinity for apoE

Question 11

Why is LDL more susceptible to oxidative damage than other lipoproteins?

Answer 11

LDL has a longer half life. Macrophages take up oxidised LDL, transform to foam cells and contribute to formation of atherosclerotic plaque

Question 12

Briefly explain reverse cholesterol transport

Answer 12

HDL have the ability to remove cholesterol from cholesterol-laden cells and return it to the liver. ABCA1 protein within the (cholesterol-laden) cell facilitates transfer of cholesterol to HDL. Mature HDL taken up by liver via specific receptors. Cells requiring additional cholesterol can utilise scavenger receptor to obtain cholesterol from HDL. HDL can also exchange cholesterol ester for TAG with VLDL via action of cholesterol exchange transfer protein

Question 13

What is the rate limiting enzyme (which statins inhibit) of the cholesterol synthetic pathway?

Answer 13

HMG-CoA reductase