Lipid Transport

Question 1

Name the major groups ‘lipids’ include

Answer 1

Triacylglycerol, fatty acids, cholesterol, phospholipids, vit A D E K

Question 2

Outline the key characteristics of lipids

Answer 2

Hydrophobic,

~2% transported by albumin,

~98% carried as lipoproteins

Question 3

What do lipoprotein particles consist of?

Answer 3

Phospholipids, cholesterol, cholesterol esters, proteins, TAG

Question 4

What is cholesterol?

Answer 4

Essential component of membranes,
synthesised in liver,
precursor to steroids and bile acids,
transported as cholesterol ester

Question 5

What are the 5 classes of lipoproteins?

Answer 5

Chylomicrons,

VLDL (very low density lipoproteins),

IDL (intermediate density lipoproteins),

LDL (low density lipoproteins),

HDL (high density lipoproteins)

Question 6

What gives blood a creamy appearance?

Answer 6

High levels of chylomicrons

Question 7

What are apolipoproteins?

Answer 7

Each lipoprotein class has a complement of associated proteins = A-H = apolipoproteins.

Integral: through phospholipid bilayer
Peripheral: on top

Function =

1) package hydrophobic lipid.
2) enzyme co-factors.
3) ligands.

Question 8

How does VLDL change to LDL?

Answer 8

Through the addition of different apolipoproteins and by coming into contact with lipoprotein lipase LPL = triglycerides lost = when cholesterol content is greater than content of triglyceride = LDL

Question 9

How is LDL linked to atherosclerosis?

Answer 9

Oxidised LDL is taken up by macrophages = become foam cells = contribute to formation of plaques

Question 10

What is the function of LDL?

Answer 10

Provide cholesterol from liver to peripheral tissue

Question 11

What is the function of chylomicrons?

Answer 11

Transport dietary triacylglycerol from intestine to adipose

Question 12

Outline the role of VLDL

Answer 12

Transport triacylglycerol synthesised in liver to adipose

Question 13

Describe the function of IDL

Answer 13

Transport cholesterol synthesised in liver to tissues

Question 14

What is the function of HDL?

Answer 14

Transport excess cholesterol to liver for disposal in bile salts and to cell requiring additional amounts

Question 15

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

Answer 15

Oxidised LDL is taken up by macrophages = become foam cells = contribute to formation of atherosclerotic plaques = rupture = thrombosis = stroke/MI.

Hypercholesterolemia = depositions = xanthelasma: yellow patches on eyelids, tendon xanthoma = nodules on tendons, corneal arcus = white circles around eyes

Question 16

Explain how hyperlipoproteinaemias may be treated

Answer 16

Diet = reduce cholesterol intake.

Lifestyle = stop smoking, start exercising.

Statins = reduce cholesterol synthesis.

Bile salt sequestrants = bind bile salts in GI forcing liver to make more bile salts using up more cholesterol

Question 17

How do statins work?

Answer 17

Inhibits HMG-CoA reductase needed for the first step in cholesterol synthesis

Question 18

Which lipoprotein contains the most cholesterol?

Answer 18

LDL

Question 19

Which enzyme releases FA from chylomicrons?

Answer 19

Lipoprotein lipase

Question 20

By what mechanism are LDL taken up by peripheral tissues?

Answer 20

Receptor mediated endocytosis

Question 21

What is a normal plasma [cholesterol], and the units?

Answer 21

<5mmol/L

Question 22

What is a cholesterol ester?

Answer 22

Cholesterol + fatty acid = ester - for transport

Question 23

Outline the role of apoB-48

Answer 23

Added to chylomicrons before entering lymphatic duct

Prod from same mRNA as ApoB100 = RNA editing adding premature stop codon

Question 24

What are the characteristics of LDL?

Answer 24

Do not have ApoC or ApoE

Long half life = more susceptible to oxidative damage (macrophages then foam cells then atherosclerotic plaques)

Question 25

What are the defects in hyperlipoproteinaemias I, IIa, III?

Answer 25

I = lipoprotein lipase defect

IIa = LDL receptor defect

III = ApoE defect (associated with CHD)

Question 26

What are the signs of hypercholesterolaemia?

Answer 26

Xanthelasma

Tendon xanthoma

Corneal arcus