Free Online biochemistry lessons for medical and Allied health sciences students by Biochemistry Club
HDL (High Density Lipoproteins)
HDL acts as a scavenger. It transports cholesterol from extra hepatic tissues to the liver.
In the liver this cholesterol will be converted to bile acids or excreted as such in the bile.
There is reverse transport of cholesterol by HDL as compared to VLDL, Chylomicrons and LDL.
Increased HDL is good for health. Less than 35 mg% is atherogenic and greater than 60 mg% is good for health.
HDL is synthesized in intestine and liver.
It is small size and disc like in shape and cause Nascent HDL.
Core is made up of cholesterol ester and TAG, outer side is lipid bilayer made of phospholipids and proteins.
Proteins present in HDL are ApoA-1 (major protein 70%), ApoA-2, ApoC-1, ApoC-2, ApoC-3, ApoD and ApoE.
55% of HDL is protein.
When HDL comes in circulation it takes up LCAT enzyme that is activated by ApoA-I.
HDL takes cholesterol from extrahepatic tissues and converts them to cholesterol ester.
Cholesterol ester is more hydrophobic than free cholesterol.
Cholesterol ester forms the inner core of HDL.
HDL increases in size becomes spherical called HDL3.
It also takes some cholesterol from circulating VLDL and chylomicron remnants.
It gives cholesterol ester to them and takes up more TAG from the VLDL remnants and further increases in size called HDL 2.
HDL2 goes to the liver where there are protein receptors SR-B1 receptors.
These receptors recognize . . .
FOR COMPLETE LESSONS ON LIPID METABOLISM PLEASE VISIT THE BIOCHEMISTRY II SECTION, CLICK CURRICULUM TO VIEW THE FULL LIST AND THEN VIEW THE LESSON OF YOUR CHOICE.