Mitochondrial Fatty Acid Transport and Oxidation
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Questions and Answers

What is the primary treatment for disorders of fatty acid oxidation?

  • Metabolic studies of liver tissue
  • Supplementation with carnitine
  • Genotyping
  • Avoidance of fasting (correct)

    • What is a common feature of defects in fatty acid oxidation?

  • Sudden infant death syndrome
  • Hyperketotic hypoglycemia
  • Hypoketotic hypoglycemia (correct)
  • Reye syndrome

    • What is a diagnostic tool for FAO disorders?

  • Plasma acylcarnitine profile
  • Urine organic acids analysis
  • Genotyping
  • All of the above (correct)

    • What is a manifestation of FAO disorders in patients with certain defects?

    <p>Cardiac and skeletal muscle weakness</p> Signup and view all the answers

    What is the effect of supplementation with carnitine in patients with carnitine transport deficiency?

    <p>Improvement in cardiomyopathy</p> Signup and view all the answers

    What is a characteristic of hypoglycemia associated with FAO disorders?

    <p>Severe and persistent</p> Signup and view all the answers

    What is the impact of fasting on patients with FAO disorders?

    <p>Fasting exacerbates the clinical features</p> Signup and view all the answers

    What is the significance of dicarboxylic aciduria in FAO disorders?

    <p>It is an abnormal urine organic acid found in FAO disorders</p> Signup and view all the answers

    What happens to malonyl-CoA concentrations during fasting, starvation, exercise, and insulin resistance?

    <p>They decrease</p> Signup and view all the answers

    What is the role of CPT1 in the regulation of fatty acid β-oxidation?

    <p>It promotes fatty acid β-oxidation</p> Signup and view all the answers

    What is the end product of each round of the β-oxidation cycle?

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

    How many acetyl-CoA molecules are generated during the complete β-oxidation of palmitoyl-CoA?

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

    What is the fate of the acetyl-CoA produced during β-oxidation?

    <p>It is oxidized in the citric acid cycle</p> Signup and view all the answers

    What is the net gain of ATP per molecule of palmitic acid oxidized?

    <p>129 ATP</p> Signup and view all the answers

    What is the purpose of the mitochondrial electron transport chain in β-oxidation?

    <p>To pass electrons from FADH2 and NADH</p> Signup and view all the answers

    What is the result of the four reactions in the β-oxidation cycle?

    <p>The removal of two-carbon units from the fatty acyl-CoA</p> Signup and view all the answers

    What enzyme is involved in glyoxylate detoxification in peroxisomes?

    <p>Alanine glyoxylate aminotransferase (AGT)</p> Signup and view all the answers

    What is the result of electron transfer in various metabolic pathways in peroxisomes?

    <p>Generation of hydrogen peroxide</p> Signup and view all the answers

    What is the role of long chain fatty acyl-CoA ligase in the FAO pathway?

    <p>To attach coenzyme A (CoA) to fatty acids</p> Signup and view all the answers

    What is the end product of the FAO pathway?

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

    What is the byproduct of each cycle of the FAO pathway?

    <p>NADH, FADH2, and an acetyl-CoA</p> Signup and view all the answers

    What is the role of the citric acid cycle in the FAO pathway?

    <p>To convert acetyl-CoA into citrate</p> Signup and view all the answers

    What is the net result of the oxidation of each two carbons of a fatty acid in the FAO pathway?

    <p>Four NADH and two FADH2</p> Signup and view all the answers

    What is the final process that consumes the NADH and FADH2 generated in the FAO pathway?

    <p>Oxidative phosphorylation</p> Signup and view all the answers

    Where does fatty acid oxidation occur?

    <p>In mitochondria, peroxisomes, and ER</p> Signup and view all the answers

    What is the main source of energy in fasting conditions?

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

    What is the result of excessive flux of FFAs and elevated insulin resistance?

    <p>Overproduction of ROS and lipotoxicity</p> Signup and view all the answers

    What is the principal pathway of fatty acid oxidation?

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

    What is the function of carnitine palmitoyltransferase (CPT) 1?

    <p>To convert acyl-CoA to acylcarnitine</p> Signup and view all the answers

    What happens to long-chain fatty acids during β-oxidation?

    <p>They are broken down into acetyl-CoA</p> Signup and view all the answers

    What is the byproduct of each cycle of β-oxidation?

    <p>One acetyl-CoA, one FADH2, and one NADH</p> Signup and view all the answers

    Which fatty acids can penetrate the mitochondrial membrane by diffusion?

    <p>Short- and medium-chain fatty acids</p> Signup and view all the answers

    What is the effect of thyroid hormone on the oxidation of fatty acids in hyperthyroid patients?

    <p>It is increased</p> Signup and view all the answers

    What is the effect of thyroid hormone on FAO in hypothyroid patients?

    <p>It is decreased by 50%</p> Signup and view all the answers

    What is the effect of a mutation that causes human generalized thyroid hormone resistance on FAO in mice?

    <p>It suppresses FAO</p> Signup and view all the answers

    What is the role of thyroid hormone in the regulation of FAO in the adult brain?

    <p>It has a critical role</p> Signup and view all the answers

    What is the effect of T3 treatment on ATP production and FAO in human and mouse astrocytes?

    <p>It increases ATP production and FAO</p> Signup and view all the answers

    What is the current understanding of the mechanism by which thyroid hormone alters FAO?

    <p>It is not well understood</p> Signup and view all the answers

    What is a limitation of studying the mechanism of thyroid hormone on FAO?

    <p>The complexity of thyroid hormone signaling pathways</p> Signup and view all the answers

    What is the focus of this chapter?

    <p>The mechanism by which thyroid hormone alters FAO</p> Signup and view all the answers

    Study Notes

    Fatty Acid Oxidation and Mitochondrial Transport

    • Fatty acid oxidation is a major source of adenosine triphosphate (ATP) in tissues such as liver, skeletal muscle, and heart, especially in fasting conditions where glucose availability is limited.
    • The primary treatment of fatty acid oxidation disorders is avoidance of fasting, as conditions that promote a decline in malonyl-CoA concentrations (e.g., fasting, starvation, exercise, and insulin resistance) act to promote fatty acid β-oxidation.

    Mitochondrial Fatty Acid Transport

    • Carnitine uptake, mitochondrial transport, and oxidation of fatty acids are key steps in fatty acid metabolism.
    • The carnitine palmitoyltransferase (CPT) system is responsible for transporting fatty acyl-CoA across the mitochondrial membranes into the matrix prior to β-oxidation.
    • Carnitine palmitoyltransferase 1 (CPT 1) converts acyl-CoA (long chain) to acylcarnitine, which is then shuttled inside by carnitine acylcarnitine translocase, and finally reconverted to acyl-CoA by CPT 2.

    Fatty Acid β-Oxidation

    • Fatty acid β-oxidation is a cyclic process where fatty acids of short, medium, and long chains are broken down within mitochondria.
    • Each cycle of β-oxidation removes two carbon atoms from the fatty acid chain, producing acetyl-CoA, FADH2, and NADH.
    • The acetyl-CoA produced by β-oxidation is normally oxidized in the citric acid (Krebs) cycle, while the FADH2 and NADH pass their electrons to the mitochondrial electron transport chain.

    Oxidation of Fatty Acids and Thyroid Hormone

    • Thyroid hormone regulates fatty acid oxidation (FAO) in the brain, which is critical for cognitive function.
    • Hyperthyroid patients exhibit an increased oxidation of fatty acids into carbon dioxide or ketone bodies, while FAO in hypothyroid patients is decreased.
    • Thyroid hormone rapidly increases ATP production and FAO in astrocytes, demonstrating its importance in brain function.

    Obesity and Nonalcoholic Fatty Liver Disease

    • Fatty acid oxidation can occur in the mitochondria, peroxisomes, and ER, and is a major source of ATP in tissues such as liver, skeletal muscle, and heart.
    • Excessive flux of free fatty acids and elevated insulin resistance lead to an overproduction of ROS and lipotoxicity in peroxisomes and ER.
    • β-oxidation is a cyclic process where fatty acids of short, medium, and long chains are broken down within mitochondria, and is necessary for long-chain fatty acids such as palmitoyl-CoA, oleoyl-CoA, and linoleoyl-CoA.

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    Description

    This quiz covers the key steps in carnitine uptake, mitochondrial transport, and oxidation of fatty acids, as well as genetic disorders affecting fatty acid metabolism and mitochondrial function.

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