Lipoproteins Notes

Lipoprotein metabolism and lipid disorders

Functions of lipids

-Energy: Triacylglycerides, fatty acids-very reduced so large amounts of energy are released per gram. Disadv: very hydrophobic, problematic for transport-Slow

-Structural: Phospholipids, cholesterol, sphingolipids

-Signalling: Prostoglandins, ionsitol lipids, steroid hormones, sphingolipids

-Involvement in inflammatory responses

Lipids in plasma

Lipids carried by lipoproteins

-Triacylglycerol: non polar

-Esterified cholesterol: Non polar

-Unesterified cholesterol: relatively polar/ampihatic

Albumin: Non esterified free fatty acids, ampiphatic, concentrations of free fatty acids (non esterified must remain very low due to their detergent like properties of dissolving membranes)

Lipoprotein particle

Core: material transported- Triacylglycerol, cholesterol ester – both very hydrophobic molecules, also fat soluable vitamins A,D,E,K, fat soluable toxins

Surface shell/monolayer: Unesterified cholesterol, monolayer of phospholipids- ampiphatic molecules that can react with both the hydrophobic and hydrophilic environments

-There are also apolipoproteins. Apolipoprotein B has a structural role, only one copy present and is a very large protein. Apolipoprotein E is a ligand for the tissues that express lipoprotein receptors. Apolipoprotein C2 is a coenzyme for lipase enzyme

Lipoprotein lipase

-Lipoprotein lipase is found attached to the endothelial cells of capillaries by a heparan sulphate proteoglycans anchor and cleaves the triglyceride from the lipoprotein-chylomicrons/Very low density lipoproteins

-Requires apolipoprotein C2 as a coactivator which is found on chylomicrons/VLDL

-This allows the triglycerides to enter tissues such as the heart/adipose tissue

-When the Triglyceride is removed the Chylomicron forms the chylomicron remnant, VLDL forms the intermediate density lipoprotein, further broken down into low density lipoprotein

Types of Lipoproteins

Exogenous pathway for lipoprotein metabolism

i) Chylomicrons: Transport Dietary Triacylglyceride, apolipoproteins: B48, A1,A2,C,E

-Synthesised in the enterocytes and released into the lacteals where they enter the systemic circulation through the thorasic duct and they bypass the portal circulation

-Apolipoprotein C2 found on the surface of the chylomicron activates Lipoprotein lipase on the surface of the endothelial cells of capillaries. The lipoprotein lipase cleaves the triglyceride...

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