Metabolism of Lipids 9 Sections27 LessonsLifetime
Lipoproteins
Lipoproteins are classified under Complex Lipids.
Definition
Lipoproteins are Physical Complex of Lipids and Proteins.
Classification
Lipoproteins are classified according to the ratio of content of the lipids and proteins.
These are present in different concentrations in different types.
The major content that are present in Lipoproteins are:
Lipids
Triacylglycerol/Triglycerides (TAGs/TGs)
Free Cholesterol (FC)
Cholesterol esters (CE)
Phospholipids (PL)
Proteins
Apo-Proteins
Apo-Protein A – Activator of LCAT.
- Apo AI
- Apo AII
- Apo AIII
Apo-Protein B – Involved in receptor-lipoprotein interactions.
- Apo B-48
- Apo B-100
Apo-Protein C – Activator of LPL.
Apo-Protein D
Apo-Protein E – Involved in receptor-lipoprotein interactions.
Apo-Protein I
Cholesterol & Cholesterol ester
Cholesterol is a steroid with steroid ring with 17-carbon ring structure and 8-carbon open chain and 3 methyl groups attached.
One OH group is attached at carbon no.3.
When a fatty acid is attached to the hydroxyl (OH) group by an ester bond, it is called Cholesterol ester (CE).
Donor of fatty acid is lecithin (enzyme is LCAT )
Lipoproteins
When Lipoproteins are centrifuged, they are separated into different bands according to their density.
Chylomicrons have the least density and biggest in size.
Chylomicrons are rich in TAGs ( about 90%).
Properties of Lipoproteins
Proteins are max. in HDL and min. in chylomicrons.
Chylomicrons have largest size and HDL smallest.
Increased level of HDL is good for health as it acts as a scavenger.
HDL takes extrahepatic cholesterol to the liver – good cholesterol.
Increased LDL is injurious to health as it has high cholesterol content which can cause atherosclerosis – bad cholesterol.
