lipoproteins Flashcards
how are most fatty acids taken up from the body?
from the diet
why are TAGs packaged into lipoproteins?
not easily transported in the blood bc they’re hydrophobic
what do lipoproteins consist of?
cholesterol and apoproteins
what are chylomicrons?
dietary TAG lipoproteins
how is liver derived TAG released?
as VLDL
what are lipoproteins?
a method of transporting TAG, cholesterol and phospholipids and some vitamins between organs and tissues
describe the structure of lipoproteins
hydrophobic core with cholesterol esters and TAG
outer layer of phospholipids, free cholesterol and apoproteins
what do apoproteins do?
control fate of lipoproteins, interact with the cellular receptors and activate/inhibit enzymes
where are apoproteins found in a lipoprotein?
embedded (e.g. apoB) or loosely bound (e.g. apoC)
what is the main component and apoprotein of chylomicron?
TAG
B48
what is the main component and apoprotein of VLDL?
TAG
B100
what is the main component and apoprotein of IDL?
TAG, cholesterol
B100
what is the main component and apoprotein of LDL?
cholesterol
B100
what is the main component and apoprotein of of HDL?
protein
AI, AII, C, E
what does apoB100 do?
controls metabolism of LDL
what does apoB48 do?
controls chylomicrons
what does apoE do?
controls receptor binding of particles –> makes the chylomicron a target for disposal
what does apoC do?
enzyme inhibitor
where is lipoprotein lipase found?
epithelium adjacent to target cells
which apoprotein activates LPL?
apoC2
what does LPL do?
degrades TAG in chylomicrons and VLDL – releases free fatty acids and glycerol for uptake by adjacent cells
where are chylomicrons formed?
in the lumen of the gut
what are chylomicrons made up of?
TAG, esterified cholesterol, phospholipids, B48
describe the life of a chylomicron?
formed in gut lumen
released by exocytosis into lacteals into the bloodstream
in the blood it exchanges components with high density lipoproteins
HDL donates ApoC-II and ApoE to chylomicron.
ApoC-II activates LPL, which breaks down TAG and unloads FAs.
Gives ApoC-II back to HDL and becomes a remnant. Bc of ApoE - taken up by liver
what is cholesterol a precursor to?
steroids and bile acids
what regulates the uptake of cholesterol into cells?
HMG-CoA
what does transcription factor SREBP do?
regulates expression of HMG-CoA reductase –> regulates how much cholesterol is taken in
where is HDL assembled?
liver and intestine
where does HDL transport cholesterol?
from peripheral tissues to the liver for disposal via bile
how does HDL scavenge free cholesterol and what does it do with it?
via the ABCA1 transporter and esterifies it to cholesterol esters
what effect do LDL and HDL have on the risk of heart disease?
LDL - increases CVD risk
HDL - cardioprotective
what conditions are caused by high TAG levels?
atherosclerosis –> risk of CHD and stroke
what condition is common In diabetes?
dyslipidaemia
what do oxidised LDLs promote?
formation of atherosclerotic plaques
what causes oxidised LDL formation?
smoking and diabetes
how does oxidised LDL lead to plaque formation?
Scavenger receptors aren’t feedback regulated by cholesterol –> macrophages become lipid laden –> foam cells –> fatty streaks in arterial wall –> plaque formation
how do statins work?
blocking HMG-CoA reductase inside the cells –> can’t make cholesterol themselves so the cells have to meet cholesterol demand by taking cholesterol from the blood
what is the mechanism of action of cholestryamine?
bind bile acids in the gut, preventing enterohepatic circulation
what are the adverse effects of cholestryamine?
GI adverse effects mainly; nausea, flatulance, abdominal bloating, alteration of bowel habit
what are the long term safety considerations of cholestryamine?
not systematically absorbed therefore the safety is good
fat soluble vitamins might be needed
