Fatty Acid Synthesis from Acetyl-CoA and Malonyl-CoA
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Questions and Answers

What is the primer molecule for the synthesis of long-chain fatty acids having an odd number of carbon atoms?

  • Pyruvate
  • Propionyl-CoA (correct)
  • Malonyl-CoA
  • Acetyl-CoA

    • What is the primary source of NADPH for lipogenesis?

  • Fatty acid oxidation
  • Citric acid cycle
  • Glycolysis
  • Pentose phosphate pathway (correct)

    • In which cellular compartment do the metabolic pathways of lipogenesis and the pentose phosphate pathway occur?

  • Endoplasmic reticulum
  • Nucleus
  • Mitochondria
  • Cytosol (correct)

    • What is the role of NADPH in fatty acid synthesis?

    <p>Donor of reducing equivalents</p> Signup and view all the answers

    What is the product of the reaction catalyzed by the 'malic enzyme'?

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

    What is the characteristic of fatty acid synthesis in mammals?

    <p>Catalyzed by individual domains of a very large polypeptide that includes an ACP domain</p> Signup and view all the answers

    What is the role of acetyl-CoA in the synthesis of palmitate?

    <p>Forms carbon atoms 15 and 16 of palmitate</p> Signup and view all the answers

    What is the function of the pentose phosphate pathway in lipogenesis?

    <p>Provides reducing equivalents for lipogenesis</p> Signup and view all the answers

    What is the role of electron-transferring flavoprotein in the reoxidation of FADH2 by the respiratory chain?

    <p>To transfer electrons from FADH2 to the respiratory chain</p> Signup and view all the answers

    What is the function of enoil-CoA hydratase in fatty acid beta-oxidation?

    <p>To add water to saturate the double bond</p> Signup and view all the answers

    What is the coenzyme involved in the dehydrogenation of the 3-hydroxy derivative?

    <p>NAD+</p> Signup and view all the answers

    What is the product of the cleavage reaction catalyzed by thiolase?

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

    What is the net reaction catalyzed by acyl-CoA acetyltransferase (thiolase)?

    <p>Thiolysis of a carbon-carbon bond</p> Signup and view all the answers

    What is the function of the trifunctional protein in fatty acid beta-oxidation?

    <p>To perform multiple steps in fatty acid beta-oxidation</p> Signup and view all the answers

    What is the result of repeating the four-step process of fatty acid beta-oxidation six more times?

    <p>The formation of eight molecules of acetyl-CoA</p> Signup and view all the answers

    What is the final destination of the acetyl-CoA produced in fatty acid beta-oxidation?

    <p>The citric acid cycle</p> Signup and view all the answers

    What is the role of FAD in the reoxidation of FADH2 by the respiratory chain?

    <p>To transfer electrons from FADH2 to the respiratory chain</p> Signup and view all the answers

    What is the substrate for the enzyme β-hydroxyacyl-CoA dehydrogenase?

    <p>3-hydroxyacyl-CoA</p> Signup and view all the answers

    What is the immediate substrate for fatty acid synthesis?

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

    What is the role of ATP in the carboxylation reaction of acetyl-CoA?

    <p>Provides energy input for the reaction</p> Signup and view all the answers

    What is the function of biotin in the acetyl-CoA carboxylase enzyme?

    <p>Acts as a cofactor for the enzyme</p> Signup and view all the answers

    What is the end product of the fatty acid synthesis pathway?

    <p>Free palmitate</p> Signup and view all the answers

    What is the structural feature of the acetyl-CoA carboxylase enzyme?

    <p>A multienzyme protein with a variable number of identical subunits</p> Signup and view all the answers

    What is the significance of the decarboxylation reaction in fatty acid synthesis?

    <p>Drives the condensation reaction</p> Signup and view all the answers

    What is the role of Mn2+ in the fatty acid synthesis pathway?

    <p>None of the above</p> Signup and view all the answers

    What is the difference between the fatty acid synthesis pathway in bacteria and plants versus in animals?

    <p>The organization of the enzymes involved in the pathway</p> Signup and view all the answers

    Study Notes

    Fatty Acid Synthesis

    • Palmitate is synthesized from acetyl-CoA and malonyl-CoA, with acetyl-CoA forming carbon atoms 15 and 16 of palmitate.
    • The addition of subsequent C2 units is via malonyl-CoA.
    • Propionyl-CoA acts as a primer for the synthesis of long-chain fatty acids with an odd number of carbon atoms, found in ruminant fat and milk.

    NADPH and Lipogenesis

    • NADPH serves as a donor of reducing equivalents in the reduction of 3-ketoacyl and 2,3-unsaturated acyl derivatives.
    • The oxidative reactions of the pentose phosphate pathway are the chief source of hydrogen required for the reductive synthesis of fatty acids.
    • Tissues specializing in active lipogenesis (liver, adipose tissue, and lactating mammary gland) possess an active pentose phosphate pathway.
    • Both metabolic pathways are found in the cytosol of the cell, with no membranes or permeability barriers against the transfer of NADPH.

    Fatty Acid Synthesis Reaction

    • Fatty acid synthesis from acetyl-CoA and malonyl-CoA occurs by a series of reactions catalyzed by:
      • 6 different enzymes plus a separate acyl carrier protein (ACP) in bacteria.
      • Individual domains of a very large polypeptide that includes an ACP domain in mammals.

    Evolution of Mammalian Fatty Acid Synthase

    • Evolution of the mammalian fatty acid synthase has involved gene fusion.

    Production of Malonyl-CoA

    • The initial and controlling step in fatty acid synthesis is the production of malonyl-CoA.
    • Bicarbonate as a source of CO2 is required in the initial reaction for the carboxylation of acetyl-CoA to malonyl-CoA in the presence of ATP and acetyl-CoA carboxylase.
    • Acetyl-CoA carboxylase has a requirement for the vitamin biotin.

    Fatty Acid Synthesis Pathway

    • The pathway involves the input of acetyl-CoA, which is carboxylated to malonyl-CoA.
    • The reaction takes place in two steps: (1) carboxylation of biotin involving ATP and (2) transfer of the carboxyl to acetyl-CoA to form malonyl-CoA.
    • ATP-dependent carboxylation provides energy input, and the CO2 is lost later during condensation with the growing fatty acid.

    Dehydrogenation, Hydration, and Dehydrogenation

    • Step 1: Dehydrogenation of alkane to alkene is catalyzed by isoforms of acyl-CoA dehydrogenase.
    • Step 2: Hydration of alkene is catalyzed by two isoforms of enoyl-CoA hydratase.
    • Step 3: Dehydrogenation of alcohol is catalyzed by β-hydroxyacyl-CoA dehydrogenase.
    • Step 4: Transfer of fatty acid chain is catalyzed by acyl-CoA acetyltransferase (thiolase) via a covalent mechanism.

    Fatty Acid Catabolism for Energy

    • Repeating the four-step process six more times results in the complete oxidation of palmitic acid into eight molecules of acetyl-CoA.
    • FADH2 and NADH are formed in each cycle, and acetyl-CoA enters the citric acid cycle and is further oxidized into CO2, producing more GTP, NADH, and FADH2.

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    Description

    This quiz covers the synthesis of palmitate from acetyl-CoA and malonyl-CoA, including the role of propionyl-CoA and the pentose phosphate pathway as a source of NADPH. It's a crucial topic in biochemistry and lipid metabolism.

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