L14 Cholesterol and Lipoprotein Metabolism Flashcards

1
Q

What is the composition of a triglyceride?

A

Glycerol backbone and three fatty acids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the composition of a phospholipid?

A

Two fatty acids attached to glycerol and phosphate with a variable head group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are some roles of cholesterol? (good and not so good) (3)

A
  • Structural component of cell membrane for cell integrity and fluidity
  • Precursor of steroid hormones, vitamin D and bile acids
  • Accumulation in arteries leading to CHD and stroke
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where is cholesterol mainly synthesised?

A

Liver and intestine, however can be synthesised in all cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is cholesterol synthesis controlled by? (3)

A
  • Dietary intake
  • Cholesterol levels
  • Hormones
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What condition do ‘statins’ treat?

A

Hypercholesterolaemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How are cholesterol levels normally balanced?

A

Balance between intake, synthesis, use, reabsorption and excretion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is HMG-CoA reductase?

A

A rate limiting enzyme to control cholesterol synthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the structure of a lipoprotein?

A

Polar surface with phospholipids, cholesterol and proteins
Non-polar lipid core with TGs and cholesteryl esters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the main component of chylomicrons? Is it the highest or lowest density?

A

Triglycerides
Lowest density due to its high fat and low protein content

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the main component of VLDL?

A

Triglycerides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the main component of LDL?

A

Cholesterol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the main component of HDL?

A

Protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where are chylomicrons produced?

A

Inside enterocytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where are VLDLs produced?

A

In the liver from chylomicron remnants and lipids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How are LDLs produced?

A

From VLDL (via IDL) after lipoprotein lipase removes triglycerides

17
Q

Where are HDLs produced?

A

Initiated in the liver but mature in circulation

18
Q

What apo-lipoporotein is associated with HDL?

19
Q

What apo-lipoporotein is associated with LDL and VLDL?

20
Q

What apo-lipoporotein is associated with chylomicrons and chylomicron remnants?

21
Q

What is the main function of lipoproteins? (1)
What are its three pathways? (3)

A
  • Used for transporting lipids
  • Exogenous pathway - digestive system to liver
  • Endogenous pathway - liver to other tissues
  • Reverse transport - from tissues back to the liver
22
Q

What are functions of apolipoproteins? (2)

A
  • Helping stabilise lipoproteins
  • Interact with receptors on cell surfaces
23
Q

How does the exogenous lipid transport pathway work? (4 steps)

A
  • Dietary lipids are packaged into chylomicrons inside enterocytes
  • Chylomicrons are absorbed into the lymphatic system via lacteals
  • Then enter the bloodstream via thoracic and right lymphatic ducts
  • Remodelling of chylomicrons
24
Q

How do chylomicrons work? (4 steps)

A
  • Chylomicrons interact with capillaries of muscle and adipose tissue
  • Lipoprotein lipase hydrolyses TGs
  • FAs and glycerol enter the cell for storage or fuel
  • Converted into chylomicron remnants that travel back to the liver
25
How does the VLDL lipid transport pathway work? (3 steps)
- Liver produces VLDLs which carry TGs and cholesteryl esters to tissues - Lipoprotein lipase removes TGs from VLDL to cells - Removal of TGs result in VLDL remnants which are mostly returned to the liver
26
How is LDL formed? (3 steps)
- Remaining VLDL remnants in circulation become IDLs - Some IDLs are reabsorbed by the liver via LDL receptor - Remaining IDLs are hydrolysed by hepatic lipase which forms LDLs
27
What lipoprotein is the main lipoprotein that transports cholesterol to cells in the body?
LDL
28
How is LDL taken up by cells? (3 steps)
- LDL's apoB-100 binds to LDL receptor (LDLR) on the cell surface - LDLR-mediated endocytosis occurs; cell membrane encloses LDL into a vesicle which enters the cell - LDL is hydrolysed and cholesterol is released
29
What is the chain of events from an oversupply of cholesterol? (6)
- Increased intracellular cholesterol - Inhibited cholesterol synthesis - Inhibited LDLR synthesis - Down-regulation of LDLR synthesis - Decreased LDL uptake - Hypercholesterolaemia
30
What happens when there is excess LDL? (2)
- LDL accumulates in the arterial walls - May become oxidised leading to atheroma formation
31
How do HDL particles fill with cholesterol? (1)
By ApoAI binding to ABCAI
32
Describe HDL maturation (3 steps)
- HDL binding to ABCAI causes efflux of free cholesterol and phospholipids - Free cholesterol is esterified by lecithin-cholesterol acyltransferase (LCAT) and stored as cholesterol esters - Cholesterol esters move to hydrophobic core of particle and produces a mature HDL
33
Describe HDL reverse transport - direct pathway (2)
- HDL particles circulate and remove cholesterol from cells, and pick up phospholipids via phospholipid transport protein (PLTP) - HDL then delivers cholesterol to the liver or steroidogenic organs such as adrenals, testes and ovaries
34
a) What does HDL use in its indirect transport pathway? (1) b) What does it promote the transfer of? (2) c) Why is this pathway beneficial? (1)
a) Cholesteryl ester transfer protein (CETP) b) Promotes the transfer of: - TG from VLDL and LDL to HDL - Cholesterol esters from HDL to VLDL and LDL c) Enables HDLs to stay in circulation to remove cholesterol