Lipid Transport and function

Question 1

What are the 5 classes of Lipoproteins?

Answer 1

• Chylomicrons
• Very low density lipoproteins (VLDL)
• Low density lipoproteins (LDL)
• Intermediate density lipoproteins (IDL)
• High density lipoproteins (HDL)

Question 2

What is the pathway for exogenous lipids?

Answer 2

• Cholesetrol & TG from the diet are absorbed in the ileum, transport in the chylomicrons to the lymph, blood then capillaries to the muscle & adipose tissue.
• TG is hydrolysed by lipoprotein lipase -> glycerol & free fatty acids released, which are taken up into tissues.
• Remaining chylomicrons remnant with cholesteryl esters travel to liver, bind to receptors & are endocytosed.
• Cholesterol is stored, oxidised to bile acids enters the endogenous pathway.

Question 3

What is the endogenous pathway for lipids?

Answer 3

• Cholesterol & newly synthesised TG travel as VLDL to muscle & adipose tissue.
• TG is hydrolysed in the tissue by lipoprotein lipase -> glycerol & FFA.
• lipoprotein particles become smaller but retain cholesteryl esters & become LDL, which binds to LDL receptors on cells.
• Cholesterol deposited in tissue for cell membrane & other functions.
• Cholesterol can return to plasma & liver for tissues via HDL.
• Cholesterol esterified with LCFA in HDL & transferred to VLDL or LDL in plasma by cholesteryl ester transfer protein.

Question 4

How are LDL receptors recylced?

Answer 4

• LDL enter the coated pit and becomes a coated vehicle.
• Then the coated vehicle becomes a endosome and if lysosome is present it degrades LDL into cholesterol.
• Cholesterol is then used for membrane steroids hormones, bile acids, lipoproteins, regulatory actions.
• Then the receptors on the LDL are then put into a recycling vehicle which is endocytosed to the surface of the cell.