Lipid Transport Flashcards
(29 cards)
What are there main types of lipids and where are they normally found?
triacylglycerols, fatty acids, cholesterol, cholesterol esters and phospholipids are normally found in blood
Where do the lipids come from?
from the diet or have been synthesised in the body
Are lipids soluble in water?
insoluble in water
How do lipids travel in plasma if they are insoluble in water?
carried in the plasma in association with protein
98% carried as highly specialised non-covalent assemblies called lipoprotein particles, 2% (mostly fatty acids) are carried bound non-covalently to albumin
Where do albumin bound fatty acids come from and what is their use?
fatty acids released from adipose tissue during lipolysis and are used as a fuel by tissues such as muscle
why don’t blood fatty acids levels normally exceed 3 mmol/L
Albumin has a limited capacity to transport fatty acids
What are plasma lipoprotein particles?
multi-molecular complexes that contain variable amounts of different lipids (phospholipids, cholesterol, triacylglycerols and cholesterol esters) in non-covalent (mostly hydrophobic) association with specific proteins
What’s the primary function of plasma lipoprotein particles?
transport water-insoluble lipid molecules in bloodstream
What is the protein component of the lipoprotein called? and what are it’s 2 roles (general)
apoprotein, structural and functional
What is the structural role of apoproteins and how does their
involved in packaging non-water soluble lipid molecules into soluble form as multi-molecular particles. They are able to do this effectively because they contain hydrophobic regions that interact with lipid molecules and hydrophilic regions that interact with water.
What is the functional role apoproteins? how is it’s function determined?
involved in the activation of enzymes or in the recognition of cell surface receptors. particular apoprotein composition of a lipoprotein particle determines its function
What is the general structure of a lipoprotein?
spherical particles that consist of a surface coat (shell) and a hydrophobic core
What do surface coat and core contain?
surface coat contains the phospholipids, cholesterol and apoproteins. hydrophobic core contains triacylglycerols and cholesterol esters
When are lipoproteins stable? what is this dependant on?
Lipoproteins are only stable if they maintain their spherical shape, dependant on the ratio of core to surface lipids.
Are any of the components of a lipoprotein free to transfer?
Many components of the surface coat are free to transfer. The core components can only be removed by special proteins e.g. lipases and transfer proteins
What are proteins embedded in phospholipid monolayer in a lipoprotein called? what about protein on the surface?
Integral apolipoproteins, peripheral apolipoproteins
What are the 5 distinct classes of lipoproteins in order of density?
Chylomicrons, VLDL (Very Low Density Lipoproteins), IDL (Intermediate Density Lipoproteins), LDL (Low Density Lipoproteins), HDL (High Density Lipoproteins)
What are the roles of the 5 lipoprotein classes?
Chylo = Transport dietary triacylglycerols from the intestine to tissues such as adipose tissue VLDL = Transport of triacylglycerols synthesised in the liver to adipose tissue for storage IDL = Short-lived precursor for LDL, has same function LDL = Transport of cholesterol synthesised in the liver to tissues HDL = Transport of excess tissue cholesterol to the liver for disposal as bile salts
Which lipoprotein is densest, which is least dense in order.
How does protein % change density?
(Densest) HDL, LDL, IDL, VLDL, Chylomicrons (Least dense)
More protein % = denser
What are the 6 major classes for apolipoproteins?
A, B, C, D, E, H
Which apolipoproteins are used for which lipoproteins?
apoB = VLDL, IDL and LDL, apoA = HDL
What happens in chylomicron metabolism?
Chylomicrons loaded in small intestine, apoB-48 added before entering lymphatic system
Travel to thoracic duct which empties subclavian vein + aquires apoC and apoE once in the blood
apoC binds lipoprotein lipase on adipocytes + muscle, released fatty acids enter cells + depletes chylomicron fat
When triglyceride around 20%, apoC dissociates and chylomicron = chylomicron remnant
Chylomicron remnant returns to liver. LDL receptor on hepatocyte binds to apoE + chylomicron remnant taken up by receptor mediated endocytosis. lysosome release remaining contents for use in metabolism
What happens in VLDL metabolism?
apoB100 added to VLDL during formation in liver, apoC and ape added from HDL in blood
VLDL binds to lipoprotein lipase on endothelial cells in muscle+adipose tissue, starts to be depleted of triaglycerol
muscle, released FA taken up + used for energy production
adipose, FA used for re-synthesis of triaglycerol + stored ad fat
What is role of Lipoprotein Lipase? How does it do it? Where is it found? what stimulates its synthesis?
The enzyme hydrolyses triacylglycerols in lipoprotein particles, releasing fatty acids and glycerol. Tissues then take up the fatty acids and the glycerols go to the liver. removing the core triacylglycerols from lipoproteins such as chylomicrons and VLDLs. It’s attached to the inner surface of capillaries in tissues such as adipose tissue and muscle. Insulin increases the synthesis of the enzyme
