Beta-Oxidation and ATP Production
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What is the first step in the process of β-oxidation for fatty acyl-CoA?

  • Cleavage by β-ketoacyl-CoA thiolase
  • Oxidation to β-Ketoacyl-CoA
  • Formation of Enoyl-CoA (correct)
  • Hydration to 3-L-Hydroxyacyl-CoA

    • Which enzyme is responsible for the hydration step in β-oxidation?

  • β-ketoacyl-CoA thiolase
  • Enoyl-CoA hydratase (correct)
  • Acyl-CoA dehydrogenase
  • 3-L-hydroxyacyl-CoA dehydrogenase

    • During β-oxidation, what is produced when 3-L-hydroxyacyl-CoA is oxidized?

  • FADH2
  • Acetyl-CoA
  • NADH + H+ (correct)
  • Fatty acyl-CoA

    • How many ATP molecules are generated from one molecule of Palmitic Acid during complete β-oxidation?

    <p>106 ATP</p> Signup and view all the answers

    What happens during the cleavage step of β-oxidation?

    <p>Formation of Acetyl-CoA and a shorter fatty acyl-CoA</p> Signup and view all the answers

    Which of the following fatty acids produces more ATP through β-oxidation?

    <p>Stearic Acid (C18:0)</p> Signup and view all the answers

    What is the role of CoA-SH in the β-oxidation pathway?

    <p>Cleaves β-ketoacyl-CoA to form Acetyl-CoA</p> Signup and view all the answers

    What is a crucial requirement for the activation of fatty acids before β-oxidation can occur?

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

    What is the primary function of Carnitine-Acyl Carnitine Translocase (CACT)?

    <p>Facilitate the entry of acylcarnitine into mitochondria</p> Signup and view all the answers

    Which enzyme is responsible for converting LCFA-CoA to Acylcarnitine?

    <p>Carnitine Palmitoyl Transferase - 1 (CPT-1)</p> Signup and view all the answers

    What happens to carnitine after acylcarnitine is converted back to LCFA-CoA?

    <p>It is released into the cytosol</p> Signup and view all the answers

    Why can long-chain fatty acids (LCFAs) not cross the mitochondrial membrane in their CoA-activated form?

    <p>They are incompatible with the lipid bilayer</p> Signup and view all the answers

    During what conditions does the carnitine shuttle notably help regulate fatty acid availability for energy?

    <p>During periods of fasting</p> Signup and view all the answers

    Where is Carnitine Palmitoyl Transferase - 2 (CPT-2) located?

    <p>Inner mitochondrial membrane</p> Signup and view all the answers

    What is the significance of the carnitine shuttle in fatty acid metabolism?

    <p>It allows fatty acids to undergo β-oxidation for energy</p> Signup and view all the answers

    What is initially required to synthesize carnitine?

    <p>Nε-trimethyllysine (TML)</p> Signup and view all the answers

    What is the role of 3-ketoacyl-CoA transferase in the ketolysis process?

    <p>It converts acetoacetate to acetoacetyl-CoA.</p> Signup and view all the answers

    Why can't the liver perform ketolysis?

    <p>It lacks the necessary enzyme for the process.</p> Signup and view all the answers

    Which hormone is primarily responsible for activating hormone-sensitive lipase during low fuel states?

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

    What process is primarily stimulated by glucagon and epinephrine in the liver?

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

    What is a result of the breakdown of fatty acids during energy mobilization?

    <p>Production of ketone bodies</p> Signup and view all the answers

    What is the primary output of odd-chain fatty acid catabolism?

    <p>Propionyl-CoA</p> Signup and view all the answers

    What is the main energy source mobilized by the body when fuel levels are low?

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

    Which enzyme is required for the conversion of propionyl-CoA to (S)-methylmalonyl-CoA?

    <p>Propionyl-CoA Carboxylase</p> Signup and view all the answers

    What is necessary for the enzymatic reaction involving Methylmalonyl-CoA Mutase?

    <p>Vitamin B12</p> Signup and view all the answers

    Which enzyme is responsible for catalyzing the splitting of Acetoacetyl-CoA into two Acetyl-CoA molecules?

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

    What is the consequence of the liver's inability to perform ketolysis?

    <p>It primarily engages in ketogenesis.</p> Signup and view all the answers

    Which molecule is produced after the conversion of succinyl-CoA that integrates into the TCA cycle?

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

    During ketogenesis, which organ primarily produces ketone bodies?

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

    In the conversion sequence of propionyl-CoA to succinyl-CoA, which step does NOT directly consume ATP?

    <p>Conversion of (S)-methylmalonyl-CoA to (R)-methylmalonyl-CoA</p> Signup and view all the answers

    What substance is released during the conversion of malate to pyruvate?

    <p>CO2</p> Signup and view all the answers

    Which of the following is NOT a product in the pathway leading from propionyl-CoA to succinyl-CoA?

    <p>Acetyl-CoA</p> Signup and view all the answers

    What is the primary function of Acyl-CoA in fatty acid metabolism?

    <p>To activate fatty acids for β-oxidation</p> Signup and view all the answers

    Which step in the formation of Acyl-CoA involves the hydrolysis of pyrophosphate?

    <p>Hydrolysis of inorganic pyrophosphate (PPi)</p> Signup and view all the answers

    What is produced as a byproduct during the formation of Acyl-CoA?

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

    Which enzyme is responsible for the conversion of Carnitine and LCFA-CoA to Acylcarnitine?

    <p>Carnitine palmitoyl transferase - 1 (CPT-1)</p> Signup and view all the answers

    What is the role of ATP in the formation of Acyl-CoA?

    <p>To activate the fatty acid</p> Signup and view all the answers

    Why is the hydrolysis of PPi crucial in the reaction pathway of Acyl-CoA formation?

    <p>It prevents reverse reactions from occurring</p> Signup and view all the answers

    Which of the following lipids can Acyl-CoA directly contribute to the synthesis of?

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

    What is the main purpose of the carnitine shuttle mechanism?

    <p>To transport long-chain fatty acids into mitochondria</p> Signup and view all the answers

    What is the primary problem encountered during the catabolism of unsaturated fatty acids like linoleic acid?

    <p>Presence of double bonds</p> Signup and view all the answers

    Which enzyme is crucial for the isomerization step in the beta-oxidation of unsaturated fatty acids?

    <p>3,2-enoyl-CoA isomerase</p> Signup and view all the answers

    What distinguishes the beta-oxidation of very long-chain fatty acids in peroxisomes from that in mitochondria?

    <p>Direct transport system into peroxisome</p> Signup and view all the answers

    What is the role of catalase in the peroxisomal β-oxidation process?

    <p>Decompose hydrogen peroxide into water and oxygen</p> Signup and view all the answers

    Which component is NOT generated during the beta-oxidation of linoleic acid?

    <p>Carbon dioxide (CO2)</p> Signup and view all the answers

    What is the function of acyl-CoA dehydrogenase in the oxidation of VLCFAs in peroxisomes?

    <p>Converting acyl-CoA to trans-enoyl-CoA</p> Signup and view all the answers

    Which situation indicates a problem during the beta-oxidation of unsaturated fatty acids?

    <p>Formation of a 4,5-double bond</p> Signup and view all the answers

    In addition to beta-oxidation, what is another function of peroxisomes?

    <p>Synthesis of bile acids</p> Signup and view all the answers

    Study Notes

    Beta-Oxidation and ATP Production

    • Beta-oxidation is a metabolic process breaking down fatty acids to create acetyl-CoA, which enters the citric acid cycle (TCA cycle) to produce ATP.
    • Crucial for energy production during fasting or low carbohydrate intake.
    • Fatty acids are first activated by linking them to coenzyme A (CoA), requiring ATP.
    • Activated fatty acyl-CoA is transported to the mitochondria, mainly via the carnitine shuttle.

    Enzymatic Steps of Beta-Oxidation

    • Four repeating enzymatic steps oxidize fatty acyl-CoA completely.
    • Formation of Enoyl-CoA: Fatty acyl-CoA converts to trans-Δ2-enoyl-CoA by acyl-CoA dehydrogenase, using FAD and forming FADH2.
    • Hydration to 3-L-Hydroxyacyl-CoA: Trans-Δ2-enoyl-CoA hydrates to form 3-L-hydroxyacyl-CoA using enoyl-CoA hydratase.
    • Oxidation to β-Ketoacyl-CoA: 3-L-hydroxyacyl-CoA is oxidized to β-ketoacyl-CoA by 3-L-hydroxyacyl-CoA dehydrogenase, consuming NAD+ and producing NADH+H+.
    • Cleavage to Acetyl-CoA: β-ketoacyl-CoA is cleaved by β-ketoacyl-CoA thiolase, using CoA-SH, yielding acetyl-CoA and a shorter fatty acyl-CoA chain.

    Energy Yield from β-Oxidation

    • Complete β-oxidation yields significant ATP.
    • Palmitic Acid (C16:0): Produces 8 acetyl-CoA, 7 FADH2, and 7 NADH, yielding a total of 106 ATP.
    • Stearic Acid (C18:0): Produces 9 acetyl-CoA, 8 FADH2, and 8 NADH, yielding a total of 120 ATP.

    Fatty Acid Absorption and Transport

    • Short-chain fatty acids (SCFAs) and medium-chain fatty acids (MCFAs) diffuse across the plasma membrane.
    • Long-chain fatty acids (LCFAs) require transporters (e.g., FA translocase, FATP5) for transport.
    • Dietary fats form micelles aiding intestinal absorption. SCFAs/MCFAs enter the portal circulation, LCFAs are packaged into chylomicrons and enter the lymphatic system then bloodstream.

    Formation of Acyl-CoA

    • Acyl-CoA synthetase activates fatty acids.
    • Reaction summary: Fatty acid + ATP → Acyl-Adenylate (intermediate) + AMP + PPi; Acyl-Adenylate + CoA → Acyl-CoA + AMP.
    • Hydrolysis of inorganic pyrophosphate (PPi) drives the reaction forward.

    Carnitine Shuttle Mechanism

    • Carnitine shuttle transports long-chain fatty acids (LCFAs) into mitochondria for β-oxidation.
    • CPT-1 (Carnitine palmitoyl transferase 1) converts LCFA-CoA to Acylcarnitine.
    • Acylcarnitine crosses the inner mitochondrial membrane via CACT (Carnitine-acylcarnitine translocase).
    • CPT-2 converts Acylcarnitine back to LCFA-CoA inside the mitochondria.

    Importance of Carnitine in Fatty Acid Metabolism

    • Crucial for energy production.
    • Acyl-CoA is the activated form for β-oxidation.
    • Fatty acids are utilized for energy, particularly in fasting or low carbohydrate intake periods.
    • Critical in both the catabolism and anabolism of fatty acids.

    Odd-Chain Fatty Acid Catabolism

    • Odd-chain fatty acid catabolism produces propionyl-CoA (3-carbon molecule), a crucial step in integrating odd-chain fatty acid metabolism into the TCA cycle.
    • Propionyl-CoA converts to Succinyl-CoA via three enzymatic steps; propionyl-CoA carboxylase, methylmalonyl-CoA racemase, and methylmalonyl-CoA mutase.

    Ketogenesis in the Liver

    • Ketogenesis is a metabolic process converting acetyl-CoA from β-oxidation into ketone bodies.
    • Important for tissues during low carbohydrate availability or fasting
    • Key ketone bodies: acetone, acetoacetate, and β-hydroxybutyrate

    Steps of Ketogenesis

    • Formation of Acetoacetyl-CoA from two molecules of acetyl-CoA.
    • Conversion of Acetoacetyl-CoA to HMG-CoA.
    • Formation of Acetoacetate from HMG-CoA.
    • Conversion of Acetoacetate to acetone or β-hydroxybutyrate.

    Ketolysis in Peripheral Tissues

    • Peripheral tissues (e.g., brain, heart, muscles) utilize ketone bodies for energy during prolonged fasting/ketosis.
    • Ketolysis converts ketone bodies to acetyl-CoA for ATP production.
    • Key enzymes: β-hydroxybutyrate dehydrogenase, 3-ketoacyl-CoA transferase, and thiolase.

    Hormonal regulation of β-oxidation

    • Glucagon and epinephrine regulate β-oxidation.
    • Hormonal activation of hormone-sensitive lipase in adipose tissues to release fatty acids.
    • Hormonal activation of proteolyses in muscle to provide amino acids as energy source/gluconeogenesis.
    • Insulin reverses the effects of glucagon and epinephrine by promoting energy storage.

    Peroxisomal β-Oxidation

    • Peroxisomes are involved in the β oxidation of very long-chain fatty acids (VLCFAs).
    • This process involves the enzymes acyl-CoA dehydrogenase, which catalyzes the initial oxidation of the acyl-CoA molecule.
    • Other processes involve hydration, further oxidation, and thiolysis of VLCFA-CoA for production of shorter chain acyl-CoA molecules.
    • Important: The presence of catalase in peroxisomes is crucial for decomposing hydrogen peroxide (H₂O₂) generated as a byproduct of fatty acid oxidation, preventing harm to the cell.

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    Description

    This quiz explores the processes of beta-oxidation and ATP production from fatty acids. It covers the steps involved in converting fatty acyl-CoA to acetyl-CoA and the importance of this process during fasting or low carbohydrate intake. Test your knowledge of the enzymatic steps and their roles in energy metabolism.

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