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Questions and Answers
What is the primary role of glycine or taurine in the biosynthesis of bile acids?
What is the primary role of glycine or taurine in the biosynthesis of bile acids?
Which statement about the structure of cholic acid is correct?
Which statement about the structure of cholic acid is correct?
In what form are conjugated bile acids primarily found in the duodenum?
In what form are conjugated bile acids primarily found in the duodenum?
What distinguishes sodium cholate from non-conjugated bile acids?
What distinguishes sodium cholate from non-conjugated bile acids?
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Which of the following accurately describes bile acid conjugation?
Which of the following accurately describes bile acid conjugation?
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What is the primary function of lipoproteins in the body?
What is the primary function of lipoproteins in the body?
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Which lipoprotein is characterized as being the largest and having the lowest density?
Which lipoprotein is characterized as being the largest and having the lowest density?
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What type of lipids are predominantly found in low-density lipoproteins (LDL) and high-density lipoproteins (HDL)?
What type of lipids are predominantly found in low-density lipoproteins (LDL) and high-density lipoproteins (HDL)?
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What is the role of apoproteins in lipoproteins?
What is the role of apoproteins in lipoproteins?
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Which lipoprotein has the highest ratio of protein to lipid?
Which lipoprotein has the highest ratio of protein to lipid?
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Which component forms the outer layer of a lipoprotein particle?
Which component forms the outer layer of a lipoprotein particle?
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What characteristic makes chylomicrons unique compared to other lipoproteins?
What characteristic makes chylomicrons unique compared to other lipoproteins?
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What is one of the main roles of HDL cholesterol in the body?
What is one of the main roles of HDL cholesterol in the body?
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Which of the following describes the function of acyl-CoA-cholesterol acyl transferase (ACAT)?
Which of the following describes the function of acyl-CoA-cholesterol acyl transferase (ACAT)?
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What is considered an optimal level of LDL cholesterol in adults, according to the guidelines?
What is considered an optimal level of LDL cholesterol in adults, according to the guidelines?
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Which type of cholesterol is primarily associated with vasculoprotection?
Which type of cholesterol is primarily associated with vasculoprotection?
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What is the typical fate of cholesterol synthesized in the liver?
What is the typical fate of cholesterol synthesized in the liver?
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Which component is NOT typically associated with steroids?
Which component is NOT typically associated with steroids?
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For triglycerides, which level is considered optimal?
For triglycerides, which level is considered optimal?
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Which of the following statements about steroid structures is true?
Which of the following statements about steroid structures is true?
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What is the desirable total cholesterol level in mg/dL for adults?
What is the desirable total cholesterol level in mg/dL for adults?
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What transformation occurs as VLDL degrades in circulation?
What transformation occurs as VLDL degrades in circulation?
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What is the primary role of LDL particles in the body?
What is the primary role of LDL particles in the body?
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What percentage of LDL is transported back to the liver?
What percentage of LDL is transported back to the liver?
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What process is facilitated by HDL particles to benefit the body?
What process is facilitated by HDL particles to benefit the body?
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How does nascent HDL particle mature?
How does nascent HDL particle mature?
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What effect does elevated LDL levels have on health?
What effect does elevated LDL levels have on health?
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What happens to cholesterol from HDL after it reaches the liver?
What happens to cholesterol from HDL after it reaches the liver?
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Which component is NOT a part of nascent HDL structure?
Which component is NOT a part of nascent HDL structure?
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Which tissues primarily receive cholesterol from LDL for steroid hormone synthesis?
Which tissues primarily receive cholesterol from LDL for steroid hormone synthesis?
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What effect does high levels of cholesterol in the blood have on the body?
What effect does high levels of cholesterol in the blood have on the body?
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What is the role of low density lipoproteins (LDL) in the body?
What is the role of low density lipoproteins (LDL) in the body?
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Which compound is a precursor to vitamin D3?
Which compound is a precursor to vitamin D3?
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Which of the following statements about bile acids is accurate?
Which of the following statements about bile acids is accurate?
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How are bile acids primarily found in the body?
How are bile acids primarily found in the body?
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What nutrient deficiency results from insufficient sunlight exposure?
What nutrient deficiency results from insufficient sunlight exposure?
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Bile salts are formed by the conjugation of bile acids with which of the following?
Bile salts are formed by the conjugation of bile acids with which of the following?
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What is the estimated daily synthesis of bile salts?
What is the estimated daily synthesis of bile salts?
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Which type of cholesterol is associated with a higher risk of heart attack?
Which type of cholesterol is associated with a higher risk of heart attack?
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What structure do all bile acids possess?
What structure do all bile acids possess?
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Study Notes
Lipids Chemistry Lecture 3
-
Plasma Lipoproteins:
- Lipoproteins transport lipids (triacylglycerols and cholesterol) from the small intestine or liver to peripheral tissues, then back to the liver.
- Lipoproteins vary in the ratio of proteins to lipids and the specific apoproteins and lipids they contain.
- Lipoprotein particles include chylomicrons, very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL).
Lipoprotein Structure
- Lipoproteins are spherical complexes of lipids and specific proteins (apoproteins).
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Outer coat:
- Apoproteins
- Phospholipids (PL)
- Unesterified cholesterol
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Inner core:
- Triacylglycerol (TAG)
- Cholesteryl ester (CE)
Size and Density of Lipoproteins
- Lipoprotein size and protein-to-lipid ratio determine density, measured by density gradient centrifugation.
- Chylomicrons (CM) are the largest and least dense, containing the most lipid and least protein.
- VLDL and LDL are successively denser, with higher protein-to-lipid ratios.
- HDL particles are the densest.
- TAG is the main lipid in chylomicrons and VLDL, while cholesterol and phospholipids are predominant in LDL and HDL.
Composition of Lipoproteins
- The table shows the percentage composition of proteins and lipids in different lipoprotein classes (chylomicrons, VLDL, LDL, and HDL).
Apoproteins
- Apoproteins, or apolipoproteins, are the protein components of lipoproteins.
- Nine major apoprotein species (A, B, C, D, and E) and various sub-species exist.
- Apoproteins have specific amino acid sequences, chain lengths, and different physiological/biochemical properties.
- They maintain lipoprotein structure integrity.
- They act as enzyme cofactors or inhibitors (e.g., apo C-II for lipoprotein lipase).
- They act as ligands for interaction with lipoprotein receptors in tissues (e.g., apo B-100 and apo E for the LDL receptor).
Chylomicrons
- Function: transport dietary lipids from the intestine to peripheral tissues.
- Synthesis: Intestinal mucosal cells synthesize chylomicrons, which are secreted into the lymph and then blood.
- Fate: Lipoprotein lipase (LPL) in capillary walls of adipose and muscle tissue digests the triacylglycerols in chylomicrons, releasing fatty acids for use by tissues (primarily muscle, heart, and adipose tissue).
- Chylomicrons shrink and become enriched in cholesterol and proteins as they circulate.
VLDL
- Function: transport lipids from the liver to peripheral tissues.
- Origin: Produced in the liver, synthesis of triacylglycerols often from excess dietary glucose.
- Formation of LDL: VLDL lose triacylglycerols as they circulate, transforming to IDL and eventually into LDL.
LDL
- Function: deliver cholesterol to peripheral tissues.
- Composition: Rich in cholesterol and cholesterol esters.
- Fate: 60% of LDL is transported back to liver; the remaining 40% supplies cholesterol to extrahepatic tissues (like adrenocortical and gonadal cells) for steroid hormone synthesis.
- Elevated LDL levels contribute to atherosclerosis plaque formation.
HDL
- Function: remove cholesterol from peripheral tissues and return it to the liver (reverse cholesterol transport).
- Formation: Nascent HDL is synthesized by the liver and intestine.
- Maturation: HDL matures by accumulating cholesterol and phospholipids from cells lining blood vessels, transforming into a more globular shape.
- Cholesterol transport: HDL accepts free cholesterol from peripheral tissues, converting it to cholesterol esters, transporting some to VLDL/IDL/LDL and returning to the liver; the rest is transferred directly in the HDL molecule.
- HDL helps to lower blood cholesterol levels.
Reverse Cholesterol Transport
- A major HDL function is reverse cholesterol transport, removing cholesterol from cells and returning it to the liver.
- This process is crucial for reducing cellular cholesterol levels, particularly in vascular tissue.
- Esterification of cholesterol within HDL prevents it from leaving.
- High HDL levels are considered vasculoprotective.
Cholesterol
- Desired values (NIH US):
- LDL cholesterol optimal less than 100 mg/dL, borderline high 130-159 mg/dL
- HDL cholesterol greater than 40-60 mg/dL
- Total cholesterol desirable less than 200 mg/dL, borderline high 200-239 mg/dL
- Triglycerides 10-150 mg/dL
- VLDL 2-38 mg/dL
- Cholesterol synthesis in the liver:
-
- Esterification with fatty acids forming cholesterol esters.
-
- Export to peripheral tissues via lipoproteins.
-
- Conversion to bile acids for fat digestion.
-
Steroids
- Steroids are a group of plant and animal lipids that share a similar tetracyclic structure.
- Steroid nucleus: Composed of 17 carbon atoms and two methyl groups (C18, C19).
- Steroids include sterols, bile acids & salts, steroid hormones and vitamin D.
- Sterols: Hydroxyl group at C-3, aliphatic side chain at C-17.
- Cholesterol: A solid alcohol with 27 carbon atoms and a steroid nucleus.
- Properties include: amphipathic, major component of cell membranes, precursor to other steroids.
Bile Acids
- Bile acids are hydroxylated steroids synthesized from cholesterol by peroxisomal enzymes within liver cells.
- Bile acids are conjugated to taurine or glycine to form bile salts.
- Classification:
- Primary (cholic and chenodeoxycholic acid)
- Secondary (deoxycholic and lithocholic acid)
- Functions:
- Emulsify fats for digestion & absorption.
- Prevent cholesterol precipitation in bile.
- Major excretory pathway for cholesterol.
- Act as signaling molecules affecting lipid and glucose metabolism.
Steroid Hormones
- Diverse class of hormones with varying structures based on the steroid nucleus.
- Categories include mineralocorticoids, glucocorticoids, sex hormones (male and female).
- Production sites include adrenal cortex and gonads (testes or ovaries).
- Role in regulating critical bodily functions and processes.
Clinical Correlation
- Low-density lipoprotein (LDL) transports cholesterol to tissues (bad cholesterol).
- High-density lipoprotein (HDL) transports cholesterol from tissues to liver (good cholesterol).
- High LDL and low HDL are associated with elevated cardiovascular risk.
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Description
This quiz covers Lecture 3 of Lipid Chemistry, focusing on the structure and function of plasma lipoproteins. Key topics include the transport of lipids, variations in lipoprotein composition, and the size and density characteristics of different lipoproteins. Test your knowledge on these essential biological molecules!
