Cholesterol and Lipid Metabolism

Question 1

What are 3 main features of lipids?

Answer 1

insoluble (or partially soluble) in water
essential for membrane integrity and biogenesis
energy sources, precursors for hormones and signalling molecules

Question 2

How are non-polar lipids transported?

Answer 2

in the blood as lipoproteins

Question 3

Name 2 non-polar lipids.

Answer 3

cholesterol esters and triglycerides

Question 4

What are the 2 classifications of lipoproteins?

Answer 4

HDL and LDL

Question 5

Atherosclerosis is strongly associated with high HDL and low LDL.
True/False?

Answer 5

False
Elevated LDL
Decreased HDL

Question 6

Esterified cholesterol and triglycerides make up which component of lipoproteins?

Answer 6

hydrophobic core

Question 7

What makes up the hydrophilic coat of lipoproteins?

Answer 7

monolayer of amphipathic cholesterol, phospholipids & apoproteins

Question 8

Which major lipoproteins contain apoB-100?

Answer 8

LDL and VLDL particles

Question 9

Which major lipoprotein contains apoA1 and apoA2?

Answer 9

HDL

Question 10

Cylomicrons contain apoB-48 and are the largest major lipoprotein.
True/False?

Answer 10

true

Question 11

What are the roles of apoB-contiaing lipoproteins?

Answer 11

Deliver triglycerides to:
muscles for ATP synthesis
Adiopocytes for storage

Question 12

Where are chylomicrons formed and which pathway are the involved in?

Answer 12

intestinal cells

exogenous pathway

Question 13

Where are VLDL particles formed and which pathway are they involved in?

Answer 13

liver cells

endogenous pathway

Question 14

Which type of triglycerides does the exogenous pathway transport?

Answer 14

dietary triglycerides

Question 15

Which type of triglycerides does the endogenous pathway transport?

Answer 15

triglycerides synthesised in that organ i.e. the liver

Question 16

What are the 3 steps in the life-cycle of ApoB-containing liposomes?

Answer 16

1. Assembly & Activation
2. Intravascular metabolism
3. Receptor mediated clearance

Question 17

What is MTP and what does it do?

Answer 17

Microsomal Triglyceride transfer Protein

Lipidates apoB100 to form VLDL which joins with triglyceride droplets

Question 18

Where do the free fatty acids used in VLDL assembly come from?

Answer 18

adipose tissue - particularly during fasting

de novo synthesis

Question 19

How are chylomicrons and VLDL particles activated?

Answer 19

transfer of apoCII from HDL particles

Question 20

Where do VLDL particles assemble?

Answer 20

hepatocytes

Question 21

Which lypolitic enzyme is associated with capillary endothelium?

Answer 21

Lipoprotein lipase (LPL)

Question 22

What does ApoCII facilitate?

Answer 22

binding of chylomicrons + VLDL particles to LPL

Question 23

What does LPL do to core triglycerides so that they can enter tissue?

Answer 23

hydrolyses them to free fatty acids + glycerol

Question 24

What are chylomicron and VLDL remnants?

Answer 24

Particles depleted of their triglycerides, but still containing cholesteryl esters

Question 25

What happens after the chylomicrons and VLDL dissociate from LPL?

Answer 25

ApoC II is transfered to HDL in exchange for ApoE - particles are now remnants

Question 26

What is apoE?

Answer 26

a high affinity ligand for receptor mediated clearance

Question 27

What do remnants do?

Answer 27

return to liver where they are further metabolised by hepatic lipase

Question 28

What percentage of remnants are cleared by receptor mediated endocytosis into hepatocytes?

Answer 28

All of ApoB-48 containing remnants & 50% of apoB-100 containing remnants

Question 29

What is clearance of LDL particles crucially dependent upon?

Answer 29

the LDL receptor expressed by liver and other tissues

Question 30

Hepatocytes endocytose LDL particles by receptor-mediated endocytosis. What happens then within the cell?

Answer 30

cholesterol is released from cholesteryl esters by hydrolysis

Question 31

What does this released cholesterol cause?

Answer 31

inhibition of HMG-CoA reductase
down-regulation of LDL receptor expression
storage of cholesterol as cholesteryl ester

Question 32

What is HMG-CoA reductase?

Answer 32

the rate limiting enzyme in de novo cholesterol synthesis