Biochemistry of Lipid Metabolism
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Questions and Answers

What is the role of bile salts in the digestion of dietary fats?

  • They transport triacylglycerols through the bloodstream.
  • They convert triacylglycerols to fatty acids.
  • They emulsify dietary fats to form mixed micelles. (correct)
  • They enhance the absorption of fatty acids in the intestinal mucosa.
  • Which enzyme is responsible for converting triacylglycerols to fatty acids and glycerol?

  • Lipoprotein lipase (correct)
  • Gastric lipase
  • Chylomicron lipase
  • Pancreatic lipase
  • What happens to fatty acids and other breakdown products in the intestinal mucosa?

  • They remain in the gut lumen.
  • They are excreted as waste.
  • They are immediately transported to the blood.
  • They are converted back into triacylglycerols. (correct)
  • What are chylomicrons composed of?

    <p>Triacylglycerols, cholesterol, and apolipoproteins</p> Signup and view all the answers

    Where do chylomicrons primarily travel after their formation?

    <p>Through the lymphatic system and bloodstream</p> Signup and view all the answers

    What triggers the activation of lipoprotein lipase?

    <p>ApoC-II</p> Signup and view all the answers

    What is the main function of intestinal lipases?

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

    In which part of the body does the digestion and absorption of dietary lipids primarily take place?

    <p>Small intestine</p> Signup and view all the answers

    What is produced during the conversion of a fatty acid to fatty acyl–CoA?

    <p>Inorganic pyrophosphate</p> Signup and view all the answers

    Where do fatty acyl–CoA esters formed in the cell typically undergo oxidation?

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

    Which enzyme catalyzes the conversion of fatty acids to fatty acyl–CoA?

    <p>Fatty acyl–CoA synthetase</p> Signup and view all the answers

    What is the byproduct of the reaction involving fatty acyl–CoA synthetase?

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

    What is the overall change in Gibbs free energy ($ abla G$) for the reaction involving fatty acyl–CoA?

    <p>$34 kJ/mol$</p> Signup and view all the answers

    Which of the following substrates can be used to synthesize ATP in the cytosol?

    <p>Fatty acyl–CoA</p> Signup and view all the answers

    What is a common fate of glycerol once it enters glycolysis?

    <p>Conversion to D-Glyceraldehyde 3-phosphate</p> Signup and view all the answers

    What type of reaction does acyl-CoA synthetase catalyze?

    <p>Formation of a thioester linkage</p> Signup and view all the answers

    What is the end product of the reaction catalyzed by acyl-CoA synthetase?

    <p>Fatty acyl–CoA</p> Signup and view all the answers

    In which cellular compartment are fatty acyl–CoA esters formed?

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

    Which molecule is coupled to the formation of fatty acyl–CoA?

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

    What is released upon the cleavage of ATP during the reaction of forming fatty acyl–CoA?

    <p>PPi and AMP</p> Signup and view all the answers

    In what organelle does the reaction catalyzed by acyl-CoA synthetase take place?

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

    What is the role of NAD in the reactions mentioned?

    <p>As an electron carrier in redox reactions</p> Signup and view all the answers

    What is a key intermediate formed during the process of converting fatty acids to fatty acyl–CoA?

    <p>Fatty acyl–adenylate</p> Signup and view all the answers

    What is the initial substrate needed for the acyl-CoA synthetase reaction?

    <p>Fatty acid</p> Signup and view all the answers

    What type of reaction occurs when the thiol group of coenzyme A attacks the enzyme-bound mixed anhydride?

    <p>Nucleophilic attack</p> Signup and view all the answers

    What is produced when AMP is displaced in the reaction involving coenzyme A?

    <p>Fatty acyl–CoA</p> Signup and view all the answers

    Which of the following statements accurately describes the overall energy change associated with the reaction?

    <p>It is highly exergonic.</p> Signup and view all the answers

    Which enzyme is responsible for transferring the acyl group to carnitine in the mitochondrial outer membrane?

    <p>Carnitine acyltransferase I</p> Signup and view all the answers

    Where does the thioester formation reaction primarily take place?

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

    What role does carnitine play in fatty acid catabolism?

    <p>It transports fatty acyl groups into the mitochondria.</p> Signup and view all the answers

    Which statement about the acyl-carnitine/carnitine transporter is true?

    <p>It facilitates the movement of acylated carnitine across the mitochondrial membranes.</p> Signup and view all the answers

    What is the effect of the reaction's overall energy of $-19 kJ/mol$ and $-15 kJ/mol$?

    <p>It implies a spontaneous reaction.</p> Signup and view all the answers

    Which auxiliary enzyme is required along with enoyl-CoA isomerase for oxidation?

    <p>NADPH-dependent 2,4-dienoyl-CoA reductase</p> Signup and view all the answers

    What is formed as a result of the combined action of enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase?

    <p>trans-2-enoyl-CoA</p> Signup and view all the answers

    Why can the cis-3,cis-6 configuration intermediate not be used in the β-oxidation pathway?

    <p>Its double bonds are in the wrong position.</p> Signup and view all the answers

    How many passes does linoleoyl-CoA undergo in the β-oxidation cycle?

    <p>Three passes</p> Signup and view all the answers

    Which carbon fatty acid undergoes β-oxidation as described in the content?

    <p>18-carbon linoleate</p> Signup and view all the answers

    What is the main reason that oleoyl-CoA requires an additional enzyme during oxidation?

    <p>To convert the double bonds to the correct isomer</p> Signup and view all the answers

    What type of fatty acid configuration is necessary for optimal β-oxidation?

    <p>Trans-cis configuration</p> Signup and view all the answers

    How many molecules of acetyl-CoA are produced from the three passes of linoleoyl-CoA through the β-oxidation sequence?

    <p>Three molecules</p> Signup and view all the answers

    Study Notes

    Bile Salts and Lipid Digestion

    • Bile salts emulsify dietary fats in the small intestine, creating mixed micelles.
    • Intestinal lipases, activated by apoC-II, degrade triacylglycerols into fatty acids and glycerol.

    Chylomicron Formation and Transport

    • Fatty acids and other breakdown products are absorbed by the intestinal mucosa and converted back into triacylglycerols.
    • Triacylglycerols, along with cholesterol and apolipoproteins, form chylomicrons.
    • Chylomicrons pass through the lymphatic system and bloodstream to deliver fats to muscle and adipose tissues.

    Fatty Acid Activation

    • Acyl-CoA synthetases catalyze the activation of fatty acids, forming fatty acyl-CoA from fatty acids, CoA, and ATP.
    • This reaction involves a two-step process, yielding AMP and pyrophosphate (PPi) as by-products.
    • The overall reaction of fatty acid activation is exergonic, releasing 34 kJ/mol of energy.

    Entry of Fatty Acids into Mitochondria

    • Fatty acyl-CoA esters are transported across the outer mitochondrial membrane for oxidation.
    • Carnitine acyltransferase I and II facilitate the transport of fatty acids into mitochondria via the acyl-carnitine/carnitine transporter.

    β-Oxidation of Fatty Acids

    • β-oxidation of saturated fatty acids yields acetyl-CoA as a primary product.
    • Monounsaturated fatty acids require additional enzymes, such as enoyl-CoA isomerase, for proper oxidation.
    • Linoleate, an 18-carbon unsaturated fatty acid, undergoes multiple cycles of β-oxidation, resulting in acetyl-CoA production.

    Role of Enzymes in Fatty Acid Metabolism

    • Enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase are crucial for the oxidation of fatty acids with double bonds, converting incorrect configurations for proper processing.
    • The action of these enzymes enables the oxidation pathway to accommodate varied fatty acid structures and prolongs energy production from dietary fats.

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    Description

    Explore the role of bile salts and lipoprotein lipase in dietary fat emulsification and metabolism in the small intestine. This quiz covers essential concepts related to lipoprotein interactions and the importance of apoC-II in fat digestion.

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