L44-lipoprotein Remodelling

Question 1

What are Lipo proteins

Answer 1

In plasma lipids are combined with Apo proteins to form Lipo proteins
Divided into four sub groups
▪️Chylomicrons
▪️Vldl
▪️Ldl
▪️Hdl

Question 2

What is the function of Lipo proteins

Answer 2

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

Question 3

What is the structure of plasma Lipo proteins

Answer 3

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)

Question 4

What are Apoproteins

Answer 4

Proteins that bind to lipids they are either peripheral that can be transferred or integral that cannot be transferred

Question 5

Functions of ApoLipoproteins

Answer 5

▪️Solubilizing lipids in Aqueous environment
▪️Recognition sites for receptors example LDL receptor
▪️Activators for certain enzymes involve in lipoprotein metabolism

Question 6

What are the enzymes involved in Lipo protein metabolism that are activated by Apolipoproteins

Answer 6

apo-CII activates lipoprotein lipase

Apo-AI activates LCAT 

Question 7

Types of Apoproteins

Answer 7

ApoLipoprotein A
Apoprotein B(apo-B48-apo-B100)
Apoprotein C(apo-CI,apo-CII,apoCIII)
Apoprotein E

Question 8

Where does the synthesis of chylomicrons occur

Answer 8

Intestinal mucosal cells secrete nascent chylomicrons

Question 9

What is the composition of nascent chylomicrons

Answer 9

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

Question 10

How do nacesnt chylomicrons become mature chylomicrons

Answer 10

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

Question 11

What are the triglycerides in the chylomicrons hydrolyzed into and how

Answer 11

Hydrolyzed into glycerol and free fatty acids

By apoCII activating lipoprotein lipase

Question 12

What is lipoprotein lipase and where is it located

Answer 12

Clearing factor

Located in capillaries of adipose tissue and other peripheral tissue such as cardiac and skeletal muscles

Question 13

What happens by the end of chylomicron metabolism

Answer 13

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

Question 14

Where does the synthesis of VLDL occur

Answer 14

In liver

Question 15

What is the composition of VLDL

Answer 15

60% Endogenous TAG
20% cholesterol
Few phospholipids
5% proteins(apoproteins)

Question 16

What Apoproteins do VLDL contain

Answer 16

Apo B-100 and they require Apo C and Apo E

Question 17

What is the function of VLDLs

Answer 17

To carry endogenous TG from the liver to the peripheral tissues

Question 18

How do the VLDLs become small dense low density lipoproteins

Answer 18

As VLDL pass for the circulation TAG is degraded by LPL causing the VLDL dec in size and become denser

Question 19

What is transferred from VLDL to HDL

Answer 19

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

Question 20

When does nonalcoholic fatty liver occur

Answer 20

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

Question 21

Where does the production of LDL occur

Answer 21

From VLDL after most of the TAG has been degraded by LPL

Question 22

What does the composition of LDL particles

Answer 22

Contain much less TAG than VLDL
have a higher concentration of cholesterol 50%
contain phospholipids and 20% apolipoproteins

Question 23

What is the apoliporotein in LDL

Answer 23

ApoB-100

Question 24

Function of LDL

Answer 24

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

Question 25

How is the cholesterol content of the cells in LDL pathway regulated

Answer 25

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

Question 26

Why is LDL known as bad cholesterol

Answer 26

Since LDL transports cholesterol particles throughout the body and builds up in the walls of arteries making them hard and narrow(atherosclerosis)

Question 27

Normal levels of LDL

Answer 27

Less than 110mg/dl

Question 28

Function of HDL

Answer 28

▪️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

Question 29

What happens to the cholesterol taken up by HDL

Answer 29

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

Question 30

Where does the synthesis of HDL occur

Answer 30

Nascent HDL are disc shaped particle synthesize mainly by the liver

Question 31

What is the composition of HDL

Answer 31

Primarly apoproteins(A,C and E) 40%
And phospholipids 30%

Question 32

What is REVERSE CHOLESTEROL TRANSPORT

Answer 32

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

Question 33

Normal HDL levels in males and females

Answer 33

Males 40mg/dl

Females 50mg/dl

Question 34

Most useful ratio to determine levels of non HDL cholesterol

Answer 34

Total cholesterol/HDL ratio

LDL/HDL ratio