2.4 Lipoproteins and Lipid transport

Question 1

What happens to a chylomicron once its secreted from the mucosal cells?

Answer 1

the chylomicrons circulate through the lymphatic system until it reaches the superior vena cava. During their time in the lymph and continuing in their plasma, chylomicrons undergo a number of physical-chemical and metabolic changes:

1) Gain apoC-II: Activates lipoprotein lipase. Which intitiates core triacylglycerol hydrolysis.
- triacylglycerol is mostly released to adipose, muscle, heart.
- Glycerol will be recycled to liver
- Apo E has receptors in the liver and the remaining chylomicron remnant will be degraded.

Question 2

Chylomicron is essentially…….???

Answer 2

a fat droplet with triglycerols making up about 90% of its weight.

Question 3

While chylomicron is getting transferred to its desired location, what else is happening? (regards to lipoproteins)

Answer 3

a number of other lipoproteins are formed to facilitate transport through the aqueous blood system.

Question 4

Lipoprotein lipase?

Answer 4

breaks down TAGS to fatty acids and glycerol

Question 5

What’s chylomicron half-life in plasma?

Answer 5

less than a hour.

Question 6

How is chylomicrons triacylglcerol distributed?

Answer 6

80% Fatty acid: adipose, muscle, heart

20% Glycerol: recycled in liver.

Question 7

What happens when fatty acids enter the tissue?

Answer 7

They get trapped in cells by conversion to fatty acyl-coA thioesters

Question 8

What’s the enzyme used to convert fatty acids into fatty acyl-coA thioesters in cells?

Answer 8

fatty acyl-coA synthetase.

Question 9

What is a chylomicron remnant?

Answer 9

it’s the “shrunken” lipoprotein…. Whatever is left of the chylomicron after Triacylglycerol is released via fatty acid and glycerol.

Question 10

What happens to the chylomicron remnant?

Answer 10

The liver has receptors specific to APO E, which will take in the chylomicron remnant and gets degraded and recycled

Question 11

Apo C II and Apo E?

Answer 11

They are picked up from HDL into chylomicrons.
Apo C II + lipoprotein lipase: converts TAG to fatty acid and glycerol.

Apo E: liver has receptor that recognizes it and will degrade chylomicron remnants.

Question 12

Chylomicron: (composition)

Answer 12

• Largest
• lowers in density due to high lipid/protein ratio
• highest in triacylglycerols as % of weight

Question 13

VLDL (composition)

Answer 13

• Very low density lipoprotein

- 2nd highest in triacylglycerols as % of weight

Question 14

IDL (composition)

Answer 14

intermediate density lipoprotein

Question 15

LDL (composition)

Answer 15

low density lipoprotein

highest in cholesterol/cholesteryl esters as % of weight

Question 16

HDL (composition)

Answer 16

High density lipoprotein, highest in density due to high protein/lipid ratio