Lipoproteins Flashcards
Why is it more important to look at LDL than VLDL
LDL has a longer half life, 3-4 days than VLDL which has 3-4 hours
What is the function of LDL and what are the receptors for it
Its receptors are apoB-100 and apoE
Its function is to bind to the LDL to redistribute cholesterol, utilize it and excrete it
What is the function of LRP and what are its ligands
ApoE
Function is to uptake chylomicron remnants and HDL
What are the ligands for scavenger receptor and what is the function of it
Present on macrophages, uptake of LDL and HDL to form foam cells, it can potentially be a good thing or bad thing, leading or inhibiting atherosclerosis
What is the fate of fatty acids that are consumed in the diet
After hydrolysis and absorption, enterocytes convert them into tri, which are then loaded onto the chylomicrons that take it away in the lacteals.
They can either go the peripheral tissue or liver. In the periphery, LPL converts them into fatty acids and they are absorbed by the muscles and other tissues
In the liver, LRP uptakes these chylomicrons where they can stored or used for energy
What is the fate of cholesterol that enters the body
- Some of it is excreted immediately
- What is absorbed goes into the chylomicrons. LPL makes these chylomicrons into chylomicron remnants which can then go to the liver and give away their cholesterol
- In the liver, bile salts are made from cholestrol and excreted
- VLDL takes away cholestrol from the liver.
- HDL can give its cholesterol to VLDL with the help of CETP
- VLDL become LDL through the help of HTGL and LDL goes on to the peripheral tissues to deposit cholesterol
Why does VLDL has such a short half life
Either less than half of it is taken up by the liver or the other half is converted to LDL via the HTGL enzyme. Afterwards LDL goes to the peripheral tissue to give away its cholesterol
What is the receptor in the liver that takes up HDL
SR-B1
Explain the functions of LCAT and CETP
If HDL wants to sequester free cholesterol it uses the enzyme LCAT to do it whereas if HDL wants to transfer its cholesterol to LDL or VLDL it does this with the help of enzymes CETP
What transporters are important for the transfer of free cholesterol from tissues that have too much cholesterol to HDL
ABC transporters are found in cells and they are responsible for transferring excess cholesterol out of the cells that have too much cholesterol and into HDL
What is the name of the enzyme that converts cholesterol to bile acids
7alpha hydroxylase
Explain the function of ABCG5/ABCG8 and ABCB11
ABCG5/ABCG8 pumps cholesterol out of the liver cells for excretion whereas ABCB11 pumps out bile salts
What is the function of ABCA1 and ABCG1
These transporters are found in the peripheral tissues and they are responsible for pumping out cholesterol from these cells and into the HDL/blood stream or whatever the transporter is.
Tangier disease is associated with a deficiency in ABCA1
What are the exogenous and endogenous lipoprotein extraction pathways
Exogenous:
Gut to Chylomicrons to peripheral tissues where they extract the tri using enzyme LPL, this converts chylo to chylo remnants which goes back to the liver and are absorbed via the LPL Related Protein.
Endogenous:
VLDL from the liver goes to the peripheral tissue where its contents are extracted by LPL, converting it into IDL which then goes back to the liver and is converted into LDL in the sinusoids by HTGL
What are the 2 transporters important for the sequester of free cholesterol from the peripheral tissues
ABCA1 and ABCG1
ABCA1 is important for interacting Apo-A
