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Questions and Answers
What is the primary component of the nonpolar core in plasma lipoproteins?
What is the primary component of the nonpolar core in plasma lipoproteins?
Which of the following is NOT a component of the hydrophilic outer layer of plasma lipoproteins?
Which of the following is NOT a component of the hydrophilic outer layer of plasma lipoproteins?
The presence of which component is crucial for the solubility of lipoproteins in plasma?
The presence of which component is crucial for the solubility of lipoproteins in plasma?
What functional significance do lipoproteins serve in the body?
What functional significance do lipoproteins serve in the body?
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In a clinical case with elevated LDL and decreased HDL, what condition might this indicate?
In a clinical case with elevated LDL and decreased HDL, what condition might this indicate?
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Which lipoprotein is primarily responsible for transporting cholesterol back to the liver?
Which lipoprotein is primarily responsible for transporting cholesterol back to the liver?
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What role do apolipoproteins play in lipoproteins?
What role do apolipoproteins play in lipoproteins?
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What characteristic of plasma lipoproteins affects their transport efficiency in the bloodstream?
What characteristic of plasma lipoproteins affects their transport efficiency in the bloodstream?
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What is the primary site of synthesis for LDL?
What is the primary site of synthesis for LDL?
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Which component is predominant in the lipid composition of LDL?
Which component is predominant in the lipid composition of LDL?
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Which apolipoprotein is primarily associated with HDL?
Which apolipoprotein is primarily associated with HDL?
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What percentage of circulating LDL is typically cleared by the liver?
What percentage of circulating LDL is typically cleared by the liver?
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Which lipoprotein is primarily responsible for transporting cholesterol from the liver to extrahepatic tissues?
Which lipoprotein is primarily responsible for transporting cholesterol from the liver to extrahepatic tissues?
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What is a significant function of HDL in the metabolism of lipoproteins?
What is a significant function of HDL in the metabolism of lipoproteins?
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What is a key characteristic of HDL compared to other lipoproteins?
What is a key characteristic of HDL compared to other lipoproteins?
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Which receptor is primarily responsible for the uptake of LDL in tissues?
Which receptor is primarily responsible for the uptake of LDL in tissues?
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What is the primary function of chylomicrons in lipid metabolism?
What is the primary function of chylomicrons in lipid metabolism?
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What is formed when chylomicrons are metabolized by lipoprotein lipase?
What is formed when chylomicrons are metabolized by lipoprotein lipase?
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Which enzyme is responsible for converting free cholesterol into cholesteryl esters in HDL metabolism?
Which enzyme is responsible for converting free cholesterol into cholesteryl esters in HDL metabolism?
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What function does hepatic lipase serve in the metabolism of HDL?
What function does hepatic lipase serve in the metabolism of HDL?
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Which apolipoprotein is primarily associated with VLDL?
Which apolipoprotein is primarily associated with VLDL?
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What transformation occurs to nascent VLDL after it enters the circulation?
What transformation occurs to nascent VLDL after it enters the circulation?
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Which receptor is primarily involved in the selective uptake of HDL cholesterol in the liver?
Which receptor is primarily involved in the selective uptake of HDL cholesterol in the liver?
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How are chylomicron remnants removed from circulation?
How are chylomicron remnants removed from circulation?
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In the context of familial hypercholesterolemia, which symptom is commonly observed?
In the context of familial hypercholesterolemia, which symptom is commonly observed?
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What is the role of apoA1 in HDL metabolism?
What is the role of apoA1 in HDL metabolism?
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What is the primary composition of VLDL?
What is the primary composition of VLDL?
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What is the fate of intermediate density lipoproteins (IDL) after VLDL metabolism?
What is the fate of intermediate density lipoproteins (IDL) after VLDL metabolism?
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Which statement best describes the composition of nascent HDL?
Which statement best describes the composition of nascent HDL?
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Which process allows mature HDL to transfer cholesterol esters to apoB-containing particles?
Which process allows mature HDL to transfer cholesterol esters to apoB-containing particles?
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What occurs to triglycerides within mature VLDL?
What occurs to triglycerides within mature VLDL?
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What is the provisional diagnosis for a 38-year-old male with yellow skin lesions and severe xanthomas?
What is the provisional diagnosis for a 38-year-old male with yellow skin lesions and severe xanthomas?
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What is the primary role of plasma lipoproteins?
What is the primary role of plasma lipoproteins?
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Which lipoproteins are primarily responsible for transporting dietary lipids from the small intestine?
Which lipoproteins are primarily responsible for transporting dietary lipids from the small intestine?
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Which lipoprotein type is categorized based on its density as the largest?
Which lipoprotein type is categorized based on its density as the largest?
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Which apolipoprotein is primarily associated with chylomicrons?
Which apolipoprotein is primarily associated with chylomicrons?
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What describes the composition of chylomicrons?
What describes the composition of chylomicrons?
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Which classification of lipoproteins is based on electrophoretic mobility?
Which classification of lipoproteins is based on electrophoretic mobility?
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Which statement is true regarding the metabolism of chylomicrons?
Which statement is true regarding the metabolism of chylomicrons?
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Which of the following lipoproteins has the lowest density?
Which of the following lipoproteins has the lowest density?
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Study Notes
Plasma Lipoproteins
- Complex molecules organized as micelles with a nonpolar core and an outer layer of amphipathic lipids
- Lipid component: triglycerides, cholesterol, and phospholipids
- Protein component: apolipoprotein or apoprotein
Nonpolar Core
- Hydrophobic
- Triglycerides (TG)
- Cholesterol ester (CE)
Outer Layer
- Hydrophilic
- Free cholesterol
- Phospholipids
- Apoproteins
Functions of Plasma Lipoproteins
- Transport lipids in circulation
- Play a key role in transporting dietary lipids from the small intestine, transporting lipids from the liver to peripheral tissues, and transporting lipids from peripheral tissues to the liver
Classification of Plasma Lipoproteins
- Classified based on density and electrophoretic mobility
Classification Based on Density
- Chylomicrons
- Very low-density lipoproteins (VLDL)
- Low-density lipoproteins (LDL)
- High-density lipoproteins (HDL)
Classification Based on Electrophoretic Mobility
- Chylomicrons
- β-lipoproteins (LDL)
- Pre β-lipoproteins (VLDL)
- α-lipoproteins (HDL)
Chylomicrons
- Site of synthesis: intestinal mucosa
- Largest lipoproteins
- Composition: lipid core (TG 85-90% and CE), outer layer of phospholipids and cholesterol, apolipoprotien (mainly apoB-48, 1-2%)
- Function: transport dietary TG from the intestine to peripheral tissues (liver, muscle, and adipose tissue)
Chylomicron Metabolism
- Dietary TG digested in the gut to fatty acids and monoglycerides
- Fatty acids and monoglycerides absorbed into the enterocytes, resynthesized into TGs, and packaged into chylomicrons (CM)
- CM enters circulation and receives apoC-II and apoE from HDL, forming mature chylomicrons
- Lipoprotein lipase (LPL) anchored to capillary endothelium breaks down TGs of mature chylomicrons, releasing large amounts of fatty acids
- Some fatty acids taken up by skeletal and cardiac muscle for oxidation and by adipose tissue for storage, while some bind to albumin and circulate as free fatty acids (FFAs)
- Chylomicron remnants, rich in cholesterol, removed from circulation by the liver via LDL receptor (apoE receptor)
Very Low-Density Lipoproteins (VLDL)
- Site of synthesis: liver
- Composition: lipid core (TG 55% and CE), outer layer of phospholipids and cholesterol, apolipoprotien (mainly apoB-100, 7-10%)
- Function: transport TG from the liver to extrahepatic tissues (muscle and adipose tissue)
VLDL Metabolism
- In hepatocytes, TG and CE transferred to apoB-100, forming nascent VLDL released into circulation
- Nascent VLDL obtains apoC-II and apoE from circulating HDL, becoming mature VLDL
- ApoC-II in mature VLDL activates LPL to cleave stored TG into fatty acids and monoglycerides, releasing them from VLDL
- VLDL core reduced and remnant becomes intermediate-density lipoprotein (IDL)
- Remnants taken up by the liver via LDL receptor (apoB-100, apoE receptor) or further metabolized to LDL in circulation
- VLDL transports endogenous lipids from the liver to extrahepatic tissues (unlike chylomicrons, which carry exogenous dietary lipids from the intestine)
Low-Density Lipoproteins (LDL)
- Site of synthesis: blood from VLDL
- Composition: lipid core (TG 13% and CE 48%), outer layer of phospholipids (28%) and cholesterol, apolipoprotien (mainly apoB-100 and apoE, 20%)
- Function: transport cholesterol from the liver to extrahepatic tissues
LDL Metabolism
- Liver and many extrahepatic tissues express the LDL receptor (apoB-100, apoE receptor)
- Approximately 70% of circulating LDL (rich in CE and PL) cleared by the liver and 30% taken up by extrahepatic tissues
- LDL plays a key role in the formation of atherosclerotic plaques, leading to atherosclerotic cardiovascular disease (bad cholesterol)
High-Density Lipoproteins (HDL)
- Site of synthesis: liver and intestine
- Smallest lipoproteins
- Composition: lipid core (TG 3% and CE 15%), outer layer of phospholipids (25%) and cholesterol, apolipoprotien (mainly apoA, 50%)
- Function:
- Source of apoC and apoE required in the metabolism of chylomicrons and VLDL
- Uptake of free cholesterol from extrahepatic tissues and esterifying it using lecithin cholesterol acyl transferase (LCAT) enzyme, activated by apoA1
- Carry cholesterol ester to the liver (reverse cholesterol transport)
HDL Metabolism
- Nascent HDL consists of discoid phospholipid bilayers containing apoA and free cholesterol
- Free cholesterols converted into cholesteryl esters by LCAT enzyme (activated by apoA1), forming mature spherical HDL
- Cholesterol ester carried in the core of HDL particles transferred to apoB containing particles in exchange for TG by CETP enzyme
- HDL cholesterol primarily delivered to the liver via Scavenger receptor B1 (SR-B1), which promotes the selective uptake of HDL cholesterol
- Hepatic lipase hydrolyzes both TG and PL in HDL
- ApoA1 from the degradation of HDL is recycled for new HDL formation
Clinical Case Scenario: Familial Hypercholesterolemia with Xanthomas
- 38-year-old male presents with yellow skin lesions on his forearm and palmar surfaces of the hands
- Father passed away from myocardial infarction at the age of 52 years
- Physical examination reveals severe xanthomas in the upper and lower extremities
- Laboratory investigations show elevated LDL-C, total cholesterol, and decreased HDL levels
- Provisional diagnosis: familial hypercholesterolemia with xanthomas
- Possible complications: risk of premature atherosclerosis and cardiovascular disease
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Description
This quiz covers the structure and function of plasma lipoproteins, including their components and classifications. It explores the roles of lipoproteins in lipid transport within the body, as well as their classification based on density and electrophoretic mobility. Test your knowledge on the key concepts surrounding these essential molecules.
