Lipid transport Flashcards
(5 cards)
What are the different pathways of circulating lipids?
Endogenous pathway = liver release of VLDLs into circulation, with LPL hydrolysing TAGs to release FFAs, forming LDLs
FFAs and cholesterol are uptaken by peripheral tissue.
LDLs are then reabsorbed by liver by LDL receptor.
Exogenous pathway = Dietary lipids are digested and pancreatic lipase degrades TAGs into MAGs and FFAs. Long chain FFAs are esterified in enterocytes and packaged into chylomicrons, passing into lymphatic system. LPL degrades Chylomicrons into smaller, chylomicron remnants before uptake by liver.
Recycling pathway = Liver releases HDLs. Free cholesterol in HDLs are esterified into cholesterol esters by LCAT and enter hydrophobic core - enabling gradient for uptake of peripheral excess cholesterol.
Free cholesterol uptaken by HDLs using ABCs.
HDLs absorbed by liver.
What apolipoproteins are found on the different lipoproteins?
HDL contains ApoA1-ApoA3
LDL and VLDLs contain ApoB100
Chylomicrons contain ApoB48.
How does the proportion of protein and lipids differ between lipoproteins?
And sizing?
HDL about 50:50 protein and lipid.
Proportion of TAG is greatest in chylomicrons and reduces between VLDL and LDL.
Cholesterol and Cholesterol esters is greatest in LDLs…. Since transport from HDL to LDL via CETP.
Chylomicrons significantly larger (80-500nm). HDL about 10nm diameter
What phospholipids do we find in lipoprotein structures?
Highest proportion of glycerophospholipids found in HDLs.
But amongst these liporpotein structures, PE and PC are most common.
Phosphatidylethanolamine and Phosphatidylcholine.
What are roles of Apolipoproteins?
ApoA1-A3 in HDL are smaller and exchangeable.
ApoB100 and ApoB48 are larger and non-exchangeable between structures.
They are amphiphilic structures which stabilise Phospholipid monolayer which delimits the structure.
