Lippincott's Biochemistry Chapter 18 - Cholesterol, Lipoprotein, and Steroid Metabolism
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Questions and Answers

What is the primary function of cholesterol in animal tissues?

  • Serves as a primary energy source
  • Regulates blood pressure
  • Facilitates insulin production
  • Acts as a structural component of all cell membranes (correct)

    • Which lipoprotein class is primarily responsible for transporting dietary lipids from the intestines to other tissues?

  • Very Low-Density Lipoproteins (VLDL)
  • High-Density Lipoproteins (HDL)
  • Low-Density Lipoproteins (LDL)
  • Chylomicrons (correct)

    • What role do apolipoproteins play in lipid metabolism?

  • They act as energy reserves.
  • They facilitate the transport and uptake of lipoproteins. (correct)
  • They serve as structural components of cell membranes.
  • They synthesize bile acids exclusively in the liver.

    • What mechanism is primarily involved in transporting excess cholesterol from peripheral tissues back to the liver?

    <p>Reverse cholesterol transport</p> Signup and view all the answers

    What condition is primarily associated with the gradual deposition of cholesterol in blood vessels?

    <p>Atherosclerosis</p> Signup and view all the answers

    What is the primary function of apolipoprotein E in cholesterol transport?

    <p>To mediate the uptake of chylomicron remnants by the liver</p> Signup and view all the answers

    Which lipoprotein is primarily responsible for transporting triglycerides from the liver to peripheral tissues?

    <p>Very low-density lipoprotein (VLDL)</p> Signup and view all the answers

    What condition is primarily caused by a defect in the uptake of chylomicron remnants?

    <p>Type III hyperlipoproteinemia</p> Signup and view all the answers

    Which enzyme is inhibited by the endocytosed cholesterol to reduce LDL receptor expression?

    <p>HMG CoA reductase</p> Signup and view all the answers

    What is the role of cholesteryl ester transfer protein (CETP) in lipoprotein metabolism?

    <p>To facilitate the exchange of cholesteryl esters for triglycerides</p> Signup and view all the answers

    Which of the following lipoproteins is least dense and contains the highest proportion of triglycerides?

    <p>Chylomicrons</p> Signup and view all the answers

    What occurs to apo C-II after most TAG is removed from chylomicrons?

    <p>It is returned to HDL</p> Signup and view all the answers

    Defects in which receptor synthesis lead to familial hypercholesterolemia?

    <p>LDL receptors</p> Signup and view all the answers

    What process is primarily responsible for the degradation of LDL in peripheral tissues?

    <p>Receptor-mediated endocytosis</p> Signup and view all the answers

    What happens to the receptors after the lipoprotein remnants in the vesicle are degraded by lysosomal acid hydrolases?

    <p>They can be recycled.</p> Signup and view all the answers

    How does high cholesterol affect HMG CoA reductase gene expression?

    <p>It inhibits gene expression.</p> Signup and view all the answers

    What is the consequence of decreased LDL receptor gene expression?

    <p>Reduced synthesis of new LDL receptor protein.</p> Signup and view all the answers

    What primary metabolites are released from lysosomal degradation of lipoprotein remnants?

    <p>Free cholesterol, amino acids, fatty acids, and phospholipids.</p> Signup and view all the answers

    Which metabolic disorder is associated with a deficiency in the ability to hydrolyze lysosomal cholesteryl esters?

    <p>Wolman disease.</p> Signup and view all the answers

    Which function is NOT related to the role of LDL in cholesterol transport?

    <p>Inhibiting cholesterol synthesis in the liver.</p> Signup and view all the answers

    What is formed during the degradation process of lipoprotein remnants after lysosomal activity?

    <p>Free cholesterol and amino acids.</p> Signup and view all the answers

    Which of the following mechanisms regulates cholesterol homeostasis through lipoprotein interaction?

    <p>Transcriptional regulation of LDL receptor gene by SREBP-2.</p> Signup and view all the answers

    Which lipoprotein class is primarily responsible for delivering dietary cholesterol to the liver?

    <p>Chylomicrons.</p> Signup and view all the answers

    Which metabolic disorder is NOT associated with defects in specific ABC proteins?

    <p>Familial hypercholesterolemia</p> Signup and view all the answers

    What is the distinguishing feature of lipoprotein (a) compared to low-density lipoprotein (LDL)?

    <p>Presence of apo(a)</p> Signup and view all the answers

    How does a high level of lipoprotein (a) primarily influence coronary heart disease risk?

    <p>Competes with plasminogen for fibrin binding</p> Signup and view all the answers

    What genetic factor is primarily responsible for variations in circulating levels of lipoprotein (a)?

    <p>Genetic predisposition</p> Signup and view all the answers

    Which of the following apolipoproteins is associated with lipoprotein (a)?

    <p>Apo B-100</p> Signup and view all the answers

    Which dietary component has been reported to potentially increase levels of lipoprotein (a)?

    <p>Trans fatty acids</p> Signup and view all the answers

    What impact does niacin have on lipoprotein (a) levels?

    <p>Decreases Lp(a) levels</p> Signup and view all the answers

    Which condition is characterized by diseases due to decreased surfactant secretion?

    <p>Respiratory distress syndrome</p> Signup and view all the answers

    In which condition do defects in ABC proteins primarily affect bile salt secretion?

    <p>Liver disease</p> Signup and view all the answers

    What role does plasminogen play in the body related to blood clots?

    <p>Precursor to a protein that breaks down fibrin</p> Signup and view all the answers

    What condition is primarily linked to defects in the synthesis of functional LDL receptors?

    <p>Type Ila hyperlipidemia</p> Signup and view all the answers

    What role do clathrin proteins play in receptor-mediated endocytosis?

    <p>They stabilize the pits on cell membranes.</p> Signup and view all the answers

    How do chylomicron remnants and IDL enter liver cells?

    <p>By receptor-mediated endocytosis.</p> Signup and view all the answers

    What mechanism is utilized by proprotein convertase subtilisin/kexin type 9 (PCSK9) in regulating cholesterol levels?

    <p>To promote internalization and degradation of LDL receptors.</p> Signup and view all the answers

    What is the outcome of a fall in the pH within the endosome during LDL processing?

    <p>Separation of LDL from its receptor.</p> Signup and view all the answers

    Which apolipoprotein is primarily responsible for binding with LDL receptors?

    <p>Apo B-100</p> Signup and view all the answers

    What is the primary consequence of defective apo B-100 in the body?

    <p>Decreased LDL uptake by cells.</p> Signup and view all the answers

    What type of hypercholesterolemia is associated with excessive activity of PCSK9?

    <p>Familial hypercholesterolemia</p> Signup and view all the answers

    Which cellular structure plays a key role in forming endosomes from vesicles containing LDL?

    <p>Vesicles coated with clathrin</p> Signup and view all the answers

    Which of the following statements about the LDL receptor is accurate?

    <p>It is a negatively charged glycoprotein.</p> Signup and view all the answers

    What is primarily responsible for the elimination of cholesterol from the liver?

    <p>Bile salt production</p> Signup and view all the answers

    Which process primarily manages cholesterol influx into the hepatic pool?

    <p>Balanced intake from various sources</p> Signup and view all the answers

    What occurs as a result of an imbalance between cholesterol influx and efflux in the body?

    <p>Cholesterol plaque formation in blood vessels</p> Signup and view all the answers

    What is a likely consequence of excessive cholesterol accumulation in endothelial linings?

    <p>Increased risk of vascular diseases</p> Signup and view all the answers

    What role does cholesterol primarily play in cell membranes?

    <p>Regulator of membrane fluidity</p> Signup and view all the answers

    Which of the following is NOT a source of cholesterol for the liver?

    <p>Cholesterol exported from muscle tissue</p> Signup and view all the answers

    How does the liver contribute to regulating cholesterol levels?

    <p>Through a complex system of transport and biosynthesis</p> Signup and view all the answers

    What effect do high sterol levels have on the SCAP-SREBP complex?

    <p>They cause the complex to remain in the SER and prevent SREBP activation.</p> Signup and view all the answers

    What is the primary mechanism through which high sterol levels regulate HMG CoA reductase activity?

    <p>Proteasomal degradation mediated by INSIG proteins.</p> Signup and view all the answers

    Which of the following is true regarding the phosphorylation state of HMG CoA reductase?

    <p>The phosphorylated form is rendered inactive by high ATP levels.</p> Signup and view all the answers

    Which hormone is associated with activating HMG CoA reductase by promoting dephosphorylation?

    <p>Insulin</p> Signup and view all the answers

    What is one consequence of a high AMP:ATP ratio in terms of cholesterol synthesis?

    <p>Inhibition of cholesterol synthesis through AMPK activation.</p> Signup and view all the answers

    How does the SREBP-2-SCAP complex become activated?

    <p>By translocating to the Golgi after sterol levels decrease.</p> Signup and view all the answers

    What results from the retention of the SCAP-SREBP complex in the SER?

    <p>Downregulation of cholesterol synthesis.</p> Signup and view all the answers

    Which of the following accurately describes the role of SREBP-1c?

    <p>It enhances the expression of enzymes involved in fatty acid synthesis.</p> Signup and view all the answers

    What primarily mediates the degradation of HMG CoA reductase in response to high sterol levels?

    <p>Ubiquitination and subsequent proteasomal action.</p> Signup and view all the answers

    What role do bile acids play in the intestine?

    <p>They act as emulsifying agents for dietary fats.</p> Signup and view all the answers

    What is the initial step in bile acid synthesis?

    <p>Insertion of hydroxyl groups at specific positions.</p> Signup and view all the answers

    How are primary bile acids formed?

    <p>Through synthesis from cholesterol in the liver.</p> Signup and view all the answers

    What is a characteristic of taurocholic acid?

    <p>It is formed by the conjugation of bile acids with taurine.</p> Signup and view all the answers

    Which enzyme regulates the rate-limiting step in bile acid synthesis?

    <p>7-alpha-hydroxylase.</p> Signup and view all the answers

    What is the ratio of glycine to taurine in bile according to the provided information?

    <p>3:1.</p> Signup and view all the answers

    What is the effect of bile acids on the expression of 7-alpha-hydroxylase?

    <p>They downregulate its expression.</p> Signup and view all the answers

    What is the process of conjugation that bile acids undergo before leaving the liver?

    <p>Formation of an amide bond with glycine or taurine.</p> Signup and view all the answers

    Which of the following statements about primary bile acids is true?

    <p>They contain both polar and nonpolar surfaces.</p> Signup and view all the answers

    Which compound is a primary bile acid derived from cholesterol?

    <p>Cholic acid.</p> Signup and view all the answers

    What is the primary component found in very-low-density lipoprotein (VLDL)?

    <p>Endogenous triglycerides</p> Signup and view all the answers

    How are VLDL particles modified after being secreted from the liver?

    <p>They obtain apo C-II and apo E from circulating HDL.</p> Signup and view all the answers

    Which condition is characterized by an imbalance between hepatic triglyceride synthesis and VLDL secretion?

    <p>Hepatic steatosis</p> Signup and view all the answers

    What initial structure do VLDL particles develop from once secreted into the bloodstream?

    <p>Nascent VLDL</p> Signup and view all the answers

    What component of VLDL is primarily synthesized in the liver?

    <p>Triglycerides</p> Signup and view all the answers

    What is the main function of VLDL in the bloodstream?

    <p>To carry triglycerides from the liver to peripheral tissues</p> Signup and view all the answers

    Which apolipoprotein is included in nascent VLDL when secreted from the liver?

    <p>Apo B-100</p> Signup and view all the answers

    Which enzyme is responsible for the degradation of TAG in VLDL once in peripheral tissues?

    <p>Lipoprotein lipase (LPL)</p> Signup and view all the answers

    What happens to VLDL after it delivers triglycerides to peripheral tissues?

    <p>It becomes LDL.</p> Signup and view all the answers

    What is the consequence of obesity regarding VLDL secretion?

    <p>Increased secretion of VLDL</p> Signup and view all the answers

    What is the primary role of lecithin in the esterification of cholesterol?

    <p>To serve as the source of fatty acids for esterification</p> Signup and view all the answers

    Which transformation occurs as nascent HDL accumulates cholesteryl esters?

    <p>It converts from a discoidal to a spherical shape</p> Signup and view all the answers

    What function does hepatic lipase serve in the conversion of HDL2?

    <p>To degrade TAG and phospholipids</p> Signup and view all the answers

    How does CETP contribute to cholesterol metabolism?

    <p>By transferring cholesteryl esters from HDL to VLDL</p> Signup and view all the answers

    What is the consequence of cholesteryl ester accumulation in HDL particles?

    <p>It supports the continued transport of cholesteryl esters to the liver</p> Signup and view all the answers

    Match the following lipoproteins with their primary function:

    <p>VLDL = Transport triglycerides from the liver LDL = Transport cholesterol to tissues HDL = Reverse cholesterol transport Chylomicrons = Transport dietary lipids from intestines</p> Signup and view all the answers

    Match the following components of cholesterol structure with their characteristics:

    <p>Steroid nucleus = Four fused hydrocarbon rings Hydroxyl group = Located at carbon 3 of ring A Branched hydrocarbon chain = Attached to carbon 17 of the D ring Double bond = Between carbon 5 and carbon 6 in ring B</p> Signup and view all the answers

    Match the following sources of liver cholesterol with their descriptions:

    <p>De novo synthesis = Cholesterol produced within the liver Dietary absorption = Cholesterol obtained from food intake Niemann-Pick C1-like 1 protein = Facilitates intestinal uptake of cholesterol Plant sterols = Poorly absorbed by humans</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Sterols = Steroids with a branched hydrocarbon chain Hypertension = Condition linked to cholesterol accumulation Ezetimibe = Drug that reduces dietary cholesterol absorption Efflux = Cholesterol exit routes from the liver</p> Signup and view all the answers

    Match the following types of cholesterol with their associated characteristics:

    <p>HDL = High-density lipoprotein VLDL = Very-low-density lipoprotein Cholesterol = Hydrophobic compound with an 8-carbon chain Chylomicrons = Transport dietary lipids to tissues</p> Signup and view all the answers

    Match the following molecules with their primary characteristics:

    <p>Cholesterol = A sterol that is a component of cell membranes Cholesteryl esters = Esterified form of cholesterol with a fatty acid attached Plant sterols = Compounds that reduce dietary cholesterol absorption Acetyl CoA = Source of carbon atoms in cholesterol synthesis</p> Signup and view all the answers

    Match the following biological processes with their descriptions:

    <p>Cholesterol synthesis = Occurs in virtually all tissues in humans Transport of cholesterol = Requires association with lipoprotein particles Dietary strategies = Involves daily ingestion of plant sterol esters Hydrophobicity of cholesteryl esters = Prevents them from being freely found in membranes</p> Signup and view all the answers

    Match the following components involved in cholesterol metabolism:

    <p>ABCG5/8 = Transporters related to sitosterolemia NADPH = Provides reducing equivalents for cholesterol synthesis Fatty acids = Attached to cholesterol in cholesteryl esters Bile salts = Assist in solubilizing cholesterol for digestion</p> Signup and view all the answers

    Match the following health implications with their corresponding factors:

    <p>Sitosterolemia = Caused by defects in efflux transporters Elevated plasma cholesterol levels = Can be reduced by dietary plant sterols Hydrophobic cholesterol = Must be transported with proteins Low levels of cholesteryl esters = Normal condition in most cells</p> Signup and view all the answers

    Match the following statements with the associated molecules:

    <p>Cholesterol = Synthesized from acetyl CoA Plant sterols = Reduce absorption of dietary cholesterol Cholesteryl esters = Not found in membranes NADPH = Essential for cholesterol reduction during its synthesis</p> Signup and view all the answers

    Study Notes

    Cholesterol, Lipoprotein, and Steroid Metabolism

    • Cholesterol is a steroid alcohol crucial for animal tissues.
    • It is a structural component of cell membranes.
    • It is a precursor for bile acids, steroid hormones, and vitamin D.
    • The liver plays a key role in regulating cholesterol homeostasis.
    • Cholesterol can enter the hepatic pool from dietary sources and de novo synthesis in extrahepatic tissues.
    • Cholesterol is eliminated from the liver in bile as unmodified cholesterol or converted to bile salts.
    • Cholesterol is also a component of plasma lipoproteins that carry lipids.
    • Cholesterol deposition in tissues, particularly blood vessel linings, can lead to atherosclerosis.

    Cholesterol Structure

    • Cholesterol is a hydrophobic molecule.
    • It has four fused hydrocarbon rings (A-D) for its steroid nucleus.
    • It has an 8-carbon branched hydrocarbon chain attached to the D ring.
    • Ring A has a hydroxyl group at carbon 3, and ring B has a double bond between carbon 5 and carbon 6.
    • Steroids with 8-10 carbon atoms in the side chain at carbon 17 and a hydroxyl group at carbon 3 are classified as sterols.
    • Cholesterol is a kind of sterol.

    Cholesterol Synthesis

    • Cholesterol is synthesized by various tissues, with the liver, intestine, adrenal cortex, and reproductive tissues being significant contributors.
    • Acetyl coenzyme A (CoA) provides all the carbon atoms.
    • Nicotinamide adenine dinucleotide phosphate (NADPH) provides the reducing equivalents needed for synthesis.
    • The synthesis pathway is endogenic and requires enzymes in the cytosol, smooth endoplasmic reticulum (SER), and peroxisome.
    • 3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) is a key intermediate in the pathway.
    • HMG-CoA reductase is the rate-limiting step in cholesterol synthesis.
    • Enzyme regulation mechanisms help maintain balance between cholesterol synthesis and excretion.

    Cholesterol Degradation

    • Humans cannot degrade the cholesterol ring structure completely.
    • Cholesterol is eliminated from the body by conversion to bile acids and bile salts.
    • Some cholesterol is excreted in feces and secreted into the bile to be eliminated.
    • Bacteria in the intestines can deconjugate and dehydroxylate bile salts, forming secondary bile salts.

    Bile Acids and Bile Salts

    • Bile is a watery mixture of organic and inorganic compounds.
    • Phosphatidylcholine (PC) and conjugated bile salts are essential organic components.
    • Bile can be secreted directly into the duodenum or stored in the gallbladder.
    • Bile acids contain 24 carbons.
    • They have hydroxyl groups and a side chain ending in a carboxyl group.
    • Bile salts are the deprotonated forms of bile acids.
    • Bile salts are crucial emulsifiers, aiding the digestion of dietary fats.

    Plasma Lipoproteins

    • Plasma lipoproteins are spherical macromolecular complexes of lipids and proteins.
    • They transport lipids in the plasma.
    • Classes of lipoproteins include chylomicrons, VLDL, IDL, LDL, and HDL.
    • Chylomicrons transport dietary lipids.
    • VLDL transport endogenous triacylglycerol.
    • IDL are intermediates in VLDL metabolism.
    • LDL transports cholesterol to peripheral tissues.
    • HDL transport cholesterol from peripheral tissues to the liver (reverse cholesterol transport).

    Steroid Hormones

    • Cholesterol is the precursor for steroid hormones.
    • This includes glucocorticoids (e.g., cortisol), mineralocorticoids (e.g., aldosterone), and sex hormones (androgens, estrogens, progestins).
    • Steroid hormones are synthesized in the adrenal cortex, ovaries, and testes.
    • Steroid hormones are transported in the blood by binding to specific plasma proteins.
    • Synthesis involves cholesterol modification by enzymes to produce various steroid hormones.

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    Description

    Test your knowledge on cholesterol, lipoproteins, and steroid metabolism. This quiz covers the roles of cholesterol in animal tissues, its structural characteristics, and the biological pathways involved in its metabolism. Understand the critical functions and implications of cholesterol in health and disease.

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