Lipid Transport & Storage Flashcards
How are lipids transported?
Associated with a protein - 98% as lipoproteins and 2 % bound non-covalently to albumin
Describe the structure of apoproteins
Involved in packaging non-water soluble lipids into a soluble form. Contain hydrophobic and hydrophilic regions.
What are the main functions of apoproteins?
Activation of enzymes or recognition of cell surface receptors
Describe the structure of a lipoprotein
Spherical, surface coat - phospholipids, cholesterol and apoproteins, hydrophobic core - TAGs and cholesterol esters
What keeps lipoproteins stable?
Their shape which is dependent on the ratio of core to surface lipids
What is the function of chylomicrons?
Transport dietary TAGs from intestines to tissues
What is the function of VLDLs?
Transport of TAGs synthesis in liver to adipose for storage
What is the function of LDLs?
Transport of cholesterol synthesised in liver to tissues
What is the function of HDLs?
Transport of excess tissue cholesterol to liver for disposal (as bile salts)
What happens to dietary TAGs?
Hydrolysed in the small intestine by pancreatic lipase. FAs enter epithelial cells - re-esterified to TAGs and then packaged into chylomicrons
How are chylomicrons released into the blood?
Via the lymphatic system, from epithelial cells.
Which tissues do chylomicrons affect?
Tissues that express the extracellular enzyme lipoprotein lipase
What does lipoprotein lipase do?
Removes the core TAGs from lipoproteins. Hydrolyses TAGs in lipoproteins to give FAs and glycerol.
Where can you find lipoprotein lipase?
Attached the inner surface of capillaries in muscles and adipose tissue
What does lecithin:cholesterol acyltransferase (LCAT) do?
Restores stability of lipoproteins. Conversion of surface lipid to core lipid - cholesterol - cholesterol ester using FA derived from lecithin
What happens if there is a deficiency in lecithin?
Unstable lipoproteins, general failure of lipid transport. Lipid deposits occur in many tissues and can lead to atherosclerosis
How do tissues obtain cholesterol from LDLs?
Receptor-mediated endocytosis
Outline the mechanism for the uptake of cholesterol
Cells synthesise LDL receptors, bind to specific apoproteins (Apo B100) on the LDL, endocytosis, lysosomal digestion, cholesterol esters - cholesterol
What is hyperlipoproteinaemia?
Increased level of one or more of the plasma lipoproteins
Describe type 1 hyperlipoproteinaemia
Chylomicrons present in fasting glucose, caused by defective lipoprotein lipase
Describe type 2a hyperlipoproteinaemia
Raised LDL, associated with coronary artery disease that may be severe, unknown defect
Describe type 2b hyperlipoproteinaemia
Raised LDL and VLDL, associated with coronary artery disease, unknown defect
Describe type 3 hyperlipoproteinaemia
Raised LDL and chylomicrons remnants, associated with coronary artery disease, defective apoprotein (Apo E)
Describe type 4 hyperlipoproteinaemia
Raised VLDL, associated with coronary artery disease, unknown defect
Describe type 5 hyperlipoproteinaemia
Raised chylomicrons and VLDL in fasting plasma, associated with coronary artery disease, unknown defect
What is familial hypercholesterolaemia?
Condition in which there may be an absence (homozygous) or deficiency (heterozygous) of functional LDL receptors.
How can you diagnose hypercholesterolaemia?
Characterised by elevated levels of LDL and cholesterol in the plasma. Homozygotes - extensive atherosclerosis early
How would you treat hyperlipoproteinaemias?
Diet and lifestyle modifications, drug therapy (statins)
How does the liver dispose of cholesterol?
Converts it into bile. Bile salt sequestrants increase disposal from body - act by binding to bile salts in GIT, promoting their loss in faeces
What are micelles?
Small assemblies of lipid molecules surrounded by polar molecules
