L44-lipoprotein Remodelling Flashcards
What are Lipo proteins
In plasma lipids are combined with Apo proteins to form Lipo proteins Divided into four sub groups ▪️Chylomicrons ▪️Vldl ▪️Ldl ▪️Hdl
What is the function of Lipo proteins
To keep their components lipid soluble as they transport them in plasma and to provide an efficient mechanism for transporting the lipid contents to and from the tissues
What is the structure of plasma Lipo proteins
Central core formed of nonpolar lipids such as try glycerol and esterified cholesterol the outer layer contains the more polar lipids such as phospholipids and non-esterified cholesterol and proteins (Apoproteins)
What are Apoproteins
Proteins that bind to lipids they are either peripheral that can be transferred or integral that cannot be transferred
Functions of ApoLipoproteins
▪️Solubilizing lipids in Aqueous environment
▪️Recognition sites for receptors example LDL receptor
▪️Activators for certain enzymes involve in lipoprotein metabolism
What are the enzymes involved in Lipo protein metabolism that are activated by Apolipoproteins
apo-CII activates lipoprotein lipase
Apo-AI activates LCAT 
Types of Apoproteins
ApoLipoprotein A
Apoprotein B(apo-B48-apo-B100)
Apoprotein C(apo-CI,apo-CII,apoCIII)
Apoprotein E
Where does the synthesis of chylomicrons occur
Intestinal mucosal cells secrete nascent chylomicrons
What is the composition of nascent chylomicrons
Rich in triglycerides(dietary exogenous lipids)
Few cholesterol
1 to 2% Apo proteins
Apoproteins: nascent contain apo-B48 which is unique to them
Then acquire apo C and apo E
How do nacesnt chylomicrons become mature chylomicrons
They leave the intestines to the lymphatic through the thoracic duct and then to the bloodstream
when it reaches the plasma the particle is rapidly modified receiving Apo E and apo C from HDL to become a mature chylomicron
What are the triglycerides in the chylomicrons hydrolyzed into and how
Hydrolyzed into glycerol and free fatty acids
By apoCII activating lipoprotein lipase
What is lipoprotein lipase and where is it located
Clearing factor
Located in capillaries of adipose tissue and other peripheral tissue such as cardiac and skeletal muscles
What happens by the end of chylomicron metabolism
ApoLipoproteins C are returned to HDL but not Apo B or E
the remaining particle is called a chylomicron remnant and is rapidly removed from the circulation by the liver whose membranes contain Lipo proteins that recognize Apo E
Where does the synthesis of VLDL occur
In liver
What is the composition of VLDL
60% Endogenous TAG
20% cholesterol
Few phospholipids
5% proteins(apoproteins)
What Apoproteins do VLDL contain
Apo B-100 and they require Apo C and Apo E
What is the function of VLDLs
To carry endogenous TG from the liver to the peripheral tissues
How do the VLDLs become small dense low density lipoproteins
As VLDL pass for the circulation TAG is degraded by LPL causing the VLDL dec in size and become denser
What is transferred from VLDL to HDL
Surface components
Apo C and E
Not apo B-100
Some TAG in an exchange reaction that concomitantly transfers cholesteryl esters fom HDL to VLDL And is accomplished by CETP
When does nonalcoholic fatty liver occur
conditions in which there is an imbalance between hepatic TAG synthesis and the secretion of VLDL
such conditions include obesity and type two diabetes mellitus
Where does the production of LDL occur
From VLDL after most of the TAG has been degraded by LPL
What does the composition of LDL particles
Contain much less TAG than VLDL
have a higher concentration of cholesterol 50%
contain phospholipids and 20% apolipoproteins
What is the apoliporotein in LDL
ApoB-100
Function of LDL
To provide cholesterol to the peripheral tissue or return it to the liver and it’s done by binding to plasma membrane at the end receptors that recognize ApoB100 but not ApoB48
How is the cholesterol content of the cells in LDL pathway regulated
1- allosteric:Release cholesterol suppresses the formation of HMG coA reductase inhibiting de novo synthesis of cholesterol
2-LDL receptors are subjected to feedback regulation so new receptors are not synthesized and so the uptake of additional cholesterol from the plasma LDL is blocked
Why is LDL known as bad cholesterol
Since LDL transports cholesterol particles throughout the body and builds up in the walls of arteries making them hard and narrow(atherosclerosis)
Normal levels of LDL
Less than 110mg/dl
Function of HDL
▪️Serve as a circulating reservoir for apo CII and apoE
▪️Take up cholesterol from non-hepatic tissues and return it to the liver as cholesteryl esters
▪️Excellent acceptors of non esterified cholesterol as a result of their high concentration of phospholipids which are important solubilizers of cholesterol
What happens to the cholesterol taken up by HDL
Immediately esterfied by the plasma enzyme lecithin cholesterol acyltransferase(LCAT)
This enzyme is synthesize and secreted by the liver
LCAT binds to nascent HDL and it’s activated by apo A
Where does the synthesis of HDL occur
Nascent HDL are disc shaped particle synthesize mainly by the liver
What is the composition of HDL
Primarly apoproteins(A,C and E) 40% And phospholipids 30%
What is REVERSE CHOLESTEROL TRANSPORT
important process by which selective transfer of cholesterol from peripheral tissues to HDL and from HDL to the liver occurs
this is important for bile acid synthesis or disposal via the boil which is a key
component of cholesterol hemostasis
Normal HDL levels in males and females
Males 40mg/dl
Females 50mg/dl
Most useful ratio to determine levels of non HDL cholesterol
Total cholesterol/HDL ratio
LDL/HDL ratio
