Lipoprotein Metabolism Flashcards
What is the lipid element of a lipoprotein made of?
Surface coat - phospholipid + cholesterol
Inner core - triacylglycerol + cholesterol ester
What is the function of the apolipoprotein?
- structural
- enzyme inhibitors/activators
- recognition factors
Which lipoprotein is the largest and which is the smallest?
Chylomicrons –> VLDL –> IDL –> LDL –> HDL
What are the three lipoprotein pathways?
Exogenous pathway Intestine --> other tissues Endogenous pathway Liver --> other tissues Reverse cholesterol pathway Other tissues --> liver
What is Lp(a) and what is it associated with?
LDL particle with apo(a)
High amounts associated with aortic stenosis
What are the two forms of apolipoprotein B and what do they do?
ApoB 100 - LVLDL, IDL, LDL
ApoB 48 - chylomicron and remnants
maintaining structural integrity of particles
What is MTP?
Microsomal triglyceride transfer protein
- expressed in intestine and liver
What does MTP do?
- catalyses the movement of TAG and cholesterol ester between phospholipid membranes
How does the LDL receptor pathway work?
- Receptors in ‘pits’ on membrane LDL
- Most receptors are recycled, some lost
- lost receptors replaced by synthesis of new ones - Accumulation of cholesterol in cell inhibits transcription of LDL receptor genes –> reduces production of new receptors -> number of receptors decreases
- Less LDL uptake –> more LDL in blood
How does reverse cholesterol pathway work?
- preB-1 HDL picks up cholesterol from plasma membrane
- passive mechanism – cholesterol from cell moves into HDL down concentration gradient
- preB-1 binds to receptor on cell and actively promotes the efflux of cholesterol
- preB-1 HDL particles fuse together –> preB-2 HDL
o enzyme LCAT binds to preB-2 HDL particle
o apoAI activates LCAT –> converts free cholesterol into cholesterol ester
