Biochemistry of Lipoprotein Transport

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Questions and Answers

Which apolipoprotein is primarily associated with HDL and serves as a ligand for the HDL receptor?

Apo B-100

Apo E

Apo A-I (correct)

Apo C-II

Which apolipoprotein acts as an activator of lipoprotein lipase and is essential for lipid metabolism?

Apo C-II (correct)

Apo E

Apo C-I

Apo C-III

What is the primary metabolic role of Apo B-100 in the body?

Activates lecithin cholesterol acyltransferase

Functions as a ligand for HDL receptors

Inhibits lipoprotein lipase

Controls the metabolism of LDL (correct)

Which apolipoprotein is synthesized in the intestine and is a truncated form of Apo B-100?

Apo B-48 Signup and view all the answers

High levels of which apolipoprotein are associated with an increased risk of atherosclerosis?

Apo B-100 Signup and view all the answers

Which apolipoprotein serves as an inhibitor for lipoprotein lipase and is linked to the regulation of lipid metabolism?

Apo C-III Signup and view all the answers

Which of the following apolipoproteins is a strong predictor of cardiovascular disease (CVD)?

Apo A-II Signup and view all the answers

Which apolipoprotein is involved in the clearance of lipoprotein particles by serving as a ligand for the LDL receptor?

Apo E Signup and view all the answers

Which lipoproteins are primarily rich in triacylglycerols?

Very low-density lipoproteins (VLDL) Signup and view all the answers

Which of the following best describes the protein content of high-density lipoproteins (HDL)?

High protein content, low lipid content Signup and view all the answers

How are lipoproteins classified based on their characteristics?

By their size and density Signup and view all the answers

Which lipoprotein moves fastest during electrophoresis due to its composition?

High-density lipoproteins (HDL) Signup and view all the answers

Which apolipoprotein is primarily associated with low-density lipoproteins (LDL)?

ApoB Signup and view all the answers

What is a characteristic feature of lipoproteins with high lipid content?

They have low density and float on centrifugation. Signup and view all the answers

Which process best describes how HDL transfers apolipoproteins to VLDL?

Only certain apolipoproteins can be transferred between HDL and VLDL. Signup and view all the answers

What is the primary role of chylomicrons in lipid metabolism?

To transport triglycerides from the intestines to other parts of the body Signup and view all the answers

Which statement accurately describes the role of the LDL receptor?

It mediates the uptake of LDL and chylomicron remnants. Signup and view all the answers

What distinguishes the scavenger receptor from the LDL receptor?

The scavenger receptor is nonspecific and nonregulated. Signup and view all the answers

Which lipoprotein receptor is primarily responsible for mediating the uptake of cholesteryl esters from HDL particles?

Class B Scavenger Receptor B1 (SR-B1). Signup and view all the answers

High levels of which protein are closely associated with an increased risk of atherosclerosis?

Apo(a). Signup and view all the answers

Which of the following statements about lipoprotein receptors is true?

LDL receptors take up IDL and chylomicron remnants. Signup and view all the answers

In which cells is the Class B Scavenger Receptor B1 (SR-B1) primarily expressed?

In liver and steroid producing cells. Signup and view all the answers

What is the function of the LDL receptor-related protein (LRP)?

To mediate the uptake of chylomicron remnants and IDL. Signup and view all the answers

Which of the following characteristics is unique to scavenger receptors compared to LDL receptors?

They can bind chemically modified LDL. Signup and view all the answers

Study Notes

Fatty Acid Transport

Short and medium-chain fatty acids are transported in the blood bound to albumin.
Other lipids are transported in the blood as part of lipoproteins.

Lipoproteins

Lipoproteins are complexes of proteins and lipids.
Have a hydrophilic external surface composed of free cholesterol, phospholipids, and apolipoproteins.
Have a hydrophobic core composed of cholesterol esters and triacylglycerols.

Lipoprotein Classification

Lipoproteins are classified by their density, diameter, protein, phospholipid, and triacylglycerol content.

Types of Lipoproteins

Chylomicrons: Largest and least dense, primarily transport dietary triacylglycerols.
Very Low-Density Lipoproteins (VLDL): Transport triacylglycerols from the liver to tissues.
Intermediate-Density Lipoproteins (IDL): Intermediate in size and density, formed by the breakdown of VLDL.
Low-Density Lipoproteins (LDL): Primarily carry cholesterol to tissues.
High-Density Lipoproteins (HDL): Smallest and densest, transport cholesterol from tissues back to the liver.

Lipoprotein Significance

Chylomicrons and VLDL are rich in triacylglycerols.
LDL and HDL are rich in cholesterol.

Lipoprotein Separation

Lipoproteins can be separated based on their density and size using centrifugation.
Lipoproteins with high lipid content have low density and float during centrifugation.
Lipoproteins with high protein content have high density and sediment during centrifugation.

Electrophoresis

Chylomicrons (fed state) migrate the slowest during electrophoresis.
Beta lipoprotein (LDL) migrates next fastest.
Pre-beta lipoprotein (VLDL) migrates slower than LDL.
Alpha lipoprotein (HDL) migrates the fastest.

Apolipoproteins

Protein components of lipoprotein particles.
ApoB: Embedded in the particle surface, cannot be easily removed.
ApoC: Loosely bound, can be transferred between lipoproteins.

Roles of Apolipoproteins

Determine lipoprotein metabolic fate through interactions with cellular receptors.
Activate and inhibit enzymes involved in lipoprotein metabolism.

Key Apolipoproteins

Apo AI: Major component of HDL, activator of lecithin cholesterol acyltransferase (LCAT), ligand for HDL receptor.
Apo AII: Protein component of HDL, inhibitor of Lipoprotein Lipase.
Apo B100: Major structural component of VLDL, IDL, and LDL, ligand for LDL receptor.
Apo B48: Truncated form of ApoB100, controls chylomicron metabolism, not recognized by LDL receptor.
Apo CI: Inhibitor of cholesteryl ester transfer protein.
Apo CII: Activator of lipoprotein lipase.
Apo CIII: Inhibitor of lipoprotein lipase.
Apo E: Found in VLDL, HDL, chylomicrons, and chylomicron remnants, ligand for LDL receptor, controls receptor binding of remnant particles.
Apo (a): Component of lipoprotein (a), attached to Apo B-100, inhibitor of fibrinolysis, enhances lipoprotein uptake by macrophages.

Lipoprotein Receptors

LDL Receptor: Present in the liver and most tissues, recognizes ApoB100 and ApoE, mediates LDL uptake.
Scavenger Receptor: Present on cell membranes, non-specific and non-regulated, binds chemically modified LDL.
Class B Scavenger Receptor B1 (SR-B1): Expressed in liver, adrenal glands, ovaries, testes, macrophages, and other cells, mediates selective uptake of cholesterol esters from HDL.

Receptor Significance

LDL receptor regulates the uptake of LDL, chylomicron remnants, and IDL.
LRP recognizes Apo E.
SR-B1 mediates the selective uptake of cholesterol esters from HDL and facilitates cholesterol efflux.

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Description

This quiz explores the transport mechanisms of fatty acids and lipoproteins in the blood. You'll learn about the types of lipoproteins, their classifications, and their roles in lipid metabolism. Test your knowledge on how lipoproteins function and their impact on health.