Lecture 4- Lipid Transort Flashcards
Why might GP’s find lipid profiles useful?
Can look at these in blood samples and see if patient is at potential risk of atherosclerosis due to high quantities of LDL’s etc
How are lipids transported?
2% bound to albumin the rest in lipoproteins
What structure is a lipoprotein?
Amphiphatic monolayer that contains triacylglycerol inside it
Which cholesterol is bad cholesterol?
There is no such thing as bad cholesterol just the lipoproteins that carry it. Reducing cholesterol reduces the bad lipoproteins
Why is cholesterol important?
Essential component of membranes
Precursor for steroid hormones like testosterone and cortisol
Precursor of bile acids
What is cholesterol transported around the body as?
Cholesterol ester
Integral vs peripheral apoproteins?
Integral= embedded
Peripheral= on surface
What do lipoproteins carry?
Triacylglycerol
Cholesterol
Fat soluble vitamins
What are the five classes of lipoproteins?
Chylomicrons
VLDL’s
LDLs
HDLs
What are the main fat carrying lipoproteins?
Chylomicrons which transport fats from GI tract through lymph and into subclavian vein to br borough to adipose tissue etc
VLDLs
What are the mainly cholesterol transporting lipoproteins?
IDLs
HDLs
LDL’s
What is the function of HDL’s
These lipoproteins are very good for you as they transport excess cholesterol from adipose tissue etc back to the liver for disposal. Also removes cholesterol deposited in walls of blood vessels
What is the problem with LDLs?
They have a very long half life which leaves them susceptible to oxidation by free radicals. They are then consumed by macrophages who now with a high fat content become foam cells. These foam cells deposit in arteries and result in the formation of a fatty streak. This fatty streak can cause atherosclerosis and lead to angina or rupture and subsequent clotting (thrombosis) which can result in stroke or myocardial infarction
Apoprotein function?
Structural: packing water insoluble lipid
Functional: ligand for cell surface receptors (endocytosis of LDLs)
Co-factor for enzymes
What does lipoprotein lipase do?
Hydrolysed triacylglycerol in lipoproteins to fatty acid and glycerol
How are chylomicrons metabolised?
Take up fat, cholesterol and fat soluble vitamins in small intestine. Travels through lymp and thoracic duct before joining circulation at left subclavian vein. Lipoprotein lipase on walls of capillaries at muscle and adipose tissue split triacylglycerol into glycerol and fatty acids to be used by tissues. Chylomicron remnants returned to liver and taken up through receptor mediated endocytosis by hepatocytes. Remaining contents degraded by lysosomes and what’s left used in metabolism
VLDL metabolism?
Made in liver to transport synthesised fat to tissues. As fat is deposited after binding to lipoprotein lipase on endothelial walls VLDL becomes LDL and IDL
LDL and IDL metabolism
When VLDL down to 30% of contents forms IDL and at 10% forms LDL which has a high cholesterol content= problematic when consumed by macrophages
Why is LDL cleared poorly by the liver?
Lacks apoE which the liver recognises for receptor mediated endocytosis and so a lot of VDL remains in circulation
How are lipoproteins related to Kwashiorkor?
Lack of apolipoproteins results in flat accumaulation and fatty liver
How are LDL’s taken up by cells
Receptor mediated endocytosis
What are the two ways that lipoprotein contents get into cells?
Receptor mediated endocytosis and lipoprotein lipase
How are HDLs synthesised and why are they important?
Synthesised by liver and intestines in an empty form when TAGg levels are low. They can also bud off from chylomicrons and VLDL as they are digested by lipoprotein lipase. They accumulate cholesterol and phospholipids from cells lining the blood vessels
What cells often take cholesterol from HDLs?
Steroidogenic cells
