What classes of lipids are normally found in the blood?
- Fatty acids
- Cholesterol esters
Why must lipids be transported with protein in the plasma?
As they are insoluble in water
How are lipids carried in the blood?
- 98% are carried as highly specialised non-covalent assemblies called lipoprotein particles
- 2% are carried bound non-covalently to albumin
What is the main class of lipid that travels bound to albumin?
Where do the fatty acids bound to albumin come from?
They are released from adipose tissue during lipolysis
What are the fatty acids bound to albumin used for?
As a fuel by tissues, e.g. muscle
What is the result of the limited carrying capacity of albumin?
Blood fatty acid levels do not normally exceed 3mM
Why do plasma lipoproteins have a great significance in medicine?
Since disorders in their metabolism are associated with a number of important diseases, e.g. atherosclerosis and coronary artery disease
How do the classes of lipoprotein differ?
- In the lipid being transported
- In the origins of the lipid
- In the destination
What are the protein components of plasma lipoprotein particles?
What are the apoproteins involved in structurally?
Packaging non-water soluble lipids into soluble form
What allows apoproteins to package non-water soluble lipids into soluble form?
They contain hydrophobic regions that interact with lipid molecules, and hydrophilic regions that interact with water
What are apoproteins involved in functionally?
May be involved in the action of enzymes or recognition of cell surface receptors
What determines the function of a lipoprotein particle
It's apoprotein composition
Describe the structure of a lipoprotein
Sphreical particles that consist of a surface coat (shell), and a hydrophobic core
What does the surface coat of a lipoprotein particle contain?
What does the hydrophobic core of a lipoprotein contain?
Tryacylglycerol and cholesterol esters
What do lipoproteins require in order to remain stable?
Must keep their spherical shape
What is the maintenance of the spherical shape of lipoproteins dependant on?
The ratio of core to surface lipids, therefore as lipid from the hydrophobic core is removed, the surface coat must be reduced
Are the components of the surface coat of lipoproteins molecules free to transfer?
Many are, but the core components can only be removed by special proteins, e.g. lipases and transfer proteins
What are the types of lipoproteins?
What is the transport functions of chylomicrons?
Transport dietary triacylglycerols from the intestine to tissues such as adipose tissue
What is the transport function of VLDL?
Transport of triacylglycerols synthesised in the liver to adipose tissue for storage
What is the transport function of LDL?
Transport of cholesterol synthesised in liver to the tissues
What is the transport function of HDL?
Transport of excess tissue cholesterol to the liver for disposal as bile salts
What must be done to dietary lipids to allow their absorption?
They cannot be absorbed directly, and are hydrolysed in the small intestine by the enzyme pancreatic lipase that release fatty acids and glycerol
What happens to the fatty acids produced by pancreatic lipase in the digestion of dietary lipids?
They enter the epithelial cells of the small intestine, where they're re-esterified back to triacylglycerols using glycerol phosphate from glucose metabolism
What happens to the triacylglycerols produced in the epithelial cells of the small intestines?
They are packaged with other dietary lipids, e.g. cholesterol, fat soluble vitamins into chylomicrons
What happens to the chylomicrons containing the TAGs produced in the epithelial cells of the small intestines?
They are released from the epithelial cells into the blood stream via the lymphatic system, and carried tissues
What tissues are chylomicrons carried to?
Those that express extracellular enzyme lipoprotein lipase, e.g. adipose