Lipoprotein Handling Flashcards Preview

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Flashcards in Lipoprotein Handling Deck (36):

Name the two pathways by which lipoproteins can be formed?

Endogenous (made by liver in the form of VLDL) or exogenous (from dietary sources, transported in chylomicrons post-absorption in the intestines)


Describe the endogenous pathway of lipoprotein synthesis

VLDLs transport endogenously synthesised TAG from the liver to the tissues


Describe the exogenous pathway of lipoprotein synthesis

Chylomicrons transport dietary lipids, that have been absorbed by the intestine, to the tissues.


Describe the general structure of lipoprotein

Cholesterol esters and TAG are located in the hydrophobic core and the outer layer contains phospholipids, free cholesterol and apoproteins


When does endogenous fatty acid synthesis usually occur?

In the presence of excess energy intake, where fatty acids are combined with glycerol-3-phosphate to form TAG


What is the most abundant form of lipid in the body?

TAG (90% of fatty acids go on to form this)


Why does the transport of TAG require modification to become lipoprotein?

TAG is hydrophobic and therefore can't be transported in aqueous blood so it is packaged into lipoproteins to enable transport


What role do apoproteins play in lipoproteins?

Control the fate of the lipoproteins by interacting with cellular receptors as well as playing a role in activating and inhibiting enzymes


Name the 5 different types of lipoprotein in order of density, from lowest to highest.

Chylomicron, VLDL, IDL, LDL, HDL


What is the main component of chylomicron and what is it's main apoprotein?

Main component = TAG.
Main apoprotein = B48


What is the main component of VLDL and what is it's main apoprotein?

Main component = TAG
Main apoprotein = B48


What is the main component(s) of IDL and what is it's main apoprotein?

Main components: TAG and cholesterol
Main apoprotein = B100


What is the main component of LDL and what is it's main apoprotein?

Main component: cholesterol
Main apoprotein: B100


What is the main component of HDL and what is it's main apoprotein(s)?

Main component: protein
Main apoproteins: AI, AII


What is the role of the B100 apoprotein?

controls the metabolism of LDL


What is the role of the B48 apoprotein?

controls chylomicrons


What is the role of the ApoE apoprotein?

controls receptor binding of receptor particles


What is the role of the ApoC apoprotein?

acts as enzyme inhibitor


What is the function of chylomicrons?

Transport dietary TAG


What is the function of VLDLs?

Transport TAG from liver to the periphery


How are IDLs formed?

From the shrinking of VLDLs into a remnant particle (IDL)


How are LDLs formed?

From the conversion of IDL particles to LDL particles in the liver


What is the function of LDL?

Mainly contain esterified cholesterol which they deliver to the peripheral tissues


What is the function of lipoprotein lipase?

Degrades TAG in chylomicrons and VLDL to release FFA and glycerol for uptake by adjacent cells.


Describe lipoprotein lipase activity after a meal

LPL activity high in adipose tissue


Describe lipoprotein lipase activity during starvation

LPL activity high in muscle so fatty acids derived from VLDL are mainly fed into oxidation (to release energy)


Which enzyme converts IDL to LDL?

hepatic TAG lipase


Why may cells take up LDL?

if intracellular cholesterol levels decline (only if reactions to make cholesterol cease)


How do cells take up LDL?

LDL (apoB/E) receptor on the plasma membrane of the cell whereby binding causes cholesterol to be released and esterified within the cell


Why is cholesterol essential?

Essential part of cell membranes and is a precursor for bile acids and steroids


Which transcription factor regulates the expression of HMG-CoA reductase and the LDL receptor?



How may smoking/diabetes contribute to the formation of atheromatous plaques?

Oxidised LDL (free radical) generated which binds to scavenger receptor instead of LDL receptors in macrophages. Because these scavenger receptors take up cholesterol, and have no negative feedback system, the macrophages become laden with lipid and form foam cells which leads to the formation of fatty streaks in the arterial wall, leading to the formation of a plaque.


How do statins work to reduce blood cholesterol levels?

In the liver HMG-CoA reductase is an enzyme involved in cholesterol sythesis which is packaged into VLDL, statins inhibit this enzyme to reduce blood cholesterol levels


How does cholestryamine work to reduce blood cholesterol levels?

Binds bile acids in the gut to prevent enterohepatic circulation


Where are HDLs formed?

Liver and intestine


What is the role of HDL?

Scavenges free cholesterol from cell membranes via ABCA1 membrane transporter and esterifies this cholesterol. In addition, HDL transports cholesterol from the peripheral tissues to the liver for disposal as well as binding to scavenger receptors to transfer cholesterol to the cell membrane.