Fatty Acid Synthesis
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Questions and Answers

Which enzyme is responsible for the cleavage of β-HMG-CoA to form acetoacetate?

  • β-Hydroxybutyrate dehydrogenase
  • HMG-CoA lyase (correct)
  • HMG-CoA synthase
  • Thiolase
  • In which part of the cell does ketogenesis primarily occur?

  • Endoplasmic reticulum
  • Mitochondrial matrix (correct)
  • Cytosol
  • Nucleus
  • Which statement regarding the utilization of ketone bodies is correct?

  • Ketone bodies are primarily used by the brain during starvation. (correct)
  • Only the liver can utilize ketone bodies.
  • Ketone bodies can be used by erythrocytes for energy.
  • Ketone bodies are not transportable in the bloodstream.
  • What is the concentration of total ketone bodies in the blood of a well-fed individual?

    <p>0.2 mmol/L</p> Signup and view all the answers

    Which molecule serves as the precursor for ketone body synthesis?

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

    Which ketone body is formed by the reduction of acetoacetate?

    <p>β-Hydroxybutyrate</p> Signup and view all the answers

    During which metabolic circumstance does the production of ketone bodies become particularly significant?

    <p>Starvation and diabetes mellitus</p> Signup and view all the answers

    How do ketone bodies benefit peripheral tissues?

    <p>They serve as an energy source.</p> Signup and view all the answers

    What is the primary source of 2-carbon fragments used in the microsomal elongation of palmitate?

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

    Which of the following fatty acids can be directly synthesized from palmitate through desaturation?

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

    Which enzyme is responsible for introducing double bonds into fatty acids during desaturation?

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

    What distinguishes β-hydroxybutyrate from acetoacetate in terms of structure?

    <p>It has no keto group</p> Signup and view all the answers

    Which of the following fatty acids cannot be synthesized by mammals due to the lack of specific enzymes?

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

    From which acid can arachidonic acid be synthesized in mammals?

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

    Which of the following statements about ketone bodies is true?

    <p>Acetoacetate can be metabolized for energy.</p> Signup and view all the answers

    Which mechanism primarily facilitates the metabolism of short and medium-chain fatty acids in mitochondria?

    <p>Mitochondrial elongation</p> Signup and view all the answers

    Study Notes

    Synthesis of Long Chain Fatty Acids from Palmitate

    • Fatty acid elongase in the microsomal enzyme system elongates palmitate using 2-carbon fragments from malonyl-CoA and reducing equivalents from NADPH.
    • Mitochondrial elongation of fatty acids is less active, primarily elongating fatty acids with less than 16 carbons, mainly short and medium chain fatty acids, using acetyl-CoA.
    • Fatty acyl CoA desaturase system in microsomes forms unsaturated fatty acids, requiring flavin-dependent cytochrome b5 reductase, NADH, and molecular oxygen.
    • Oleic acid (from stearate) and palmitoleic acid (from palmitate) are synthesized as monounsaturated fatty acids.
    • Mammals cannot introduce double bonds between the 10th carbon and the methyl terminal (ω) end, making linoleic and linolenic acids essential dietary components.
    • Arachidonic acid can be synthesized from linoleic acid via desaturation and chain elongation, serving as a precursor for eicosanoids like prostaglandins and thromboxanes.

    Metabolism of Ketone Bodies

    • Ketone bodies (acetoacetate, β-hydroxybutyrate, and acetone) are water-soluble energy sources, with acetone exhaled and not metabolized.
    • Ketogenesis occurs exclusively in the liver, within the mitochondrial matrix of hepatic cells, utilizing acetyl-CoA derived from fatty acid oxidation, pyruvate, or specific amino acids.
    • Ketogenesis involves the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA, followed by condensation with another acetyl-CoA to create β-HMG-CoA, regulated by HMG-CoA synthase.
    • HMG-CoA is then cleaved into acetoacetate and acetyl-CoA by HMG-CoA lyase, while β-hydroxybutyrate is produced by reducing acetoacetate using β-hydroxybutyrate dehydrogenase.
    • Acetoacetate can spontaneously decarboxylate into acetone, with blood ketone body concentrations not exceeding 0.2 mmol/L in well-fed conditions.

    Utilization of Ketone Bodies

    • Ketone bodies (acetoacetate and β-hydroxybutyrate) serve as significant energy sources for peripheral tissues, including skeletal muscle and cardiac muscle.
    • Tissues such as erythrocytes, lacking mitochondria, cannot utilize ketone bodies.
    • The production and utilization of ketone bodies increase significantly under conditions of low glucose availability, observed in starvation or diabetes mellitus.
    • During prolonged starvation, ketone bodies become a primary fuel source for the brain and other central nervous system regions.

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    Description

    This quiz covers the synthesis of long chain fatty acids from palmitate, detailing the processes involving microsomal and mitochondrial elongation. Explore the roles of enzymes like fatty acid elongase and the metabolic pathways involved in fatty acid elongation. Test your understanding of these biochemical mechanisms.

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