Synthesis and Degradation of Saturated Fatty Acids Chapter 16 next 10 pages
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Questions and Answers

What hormonal state favors the synthesis of long-chain, even-numbered saturated fatty acids?

  • High insulin/glucagon ratio (correct)
  • High epinephrine/glucagon ratio
  • Low insulin/glucagon ratio
  • Low cortisol/adrenaline ratio

    • Which carrier is involved in transporting acyl/acetyl groups between mitochondria and cytosol during the synthesis of long-chain, even-numbered saturated fatty acids?

  • Carnitine
  • Coenzyme A
  • Acyl carrier protein
  • Citrate (correct)

    • Which coenzyme is used for oxidation/reduction reactions in the synthesis of long-chain, even-numbered saturated fatty acids?

  • FADH2
  • NADPH (correct)
  • Coenzyme Q
  • NADP+

    • What subcellular location is primarily associated with the degradation of long-chain, even-numbered saturated fatty acids?

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

    During the synthesis of long-chain, even-numbered saturated fatty acids, what is the two-carbon donor/product?

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

    Which compound inhibits the synthesis of long-chain, even-numbered saturated fatty acids?

    <p>Long-chain fatty acyl CoA</p> Signup and view all the answers

    Which molecule provides the highest amount of ATP during the oxidation of palmitoyl CoA?

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

    Which metabolic disorder is characterized by the inability to oxidize medium-chain fatty acids leading to hypoglycemia?

    <p>MCAD deficiency</p> Signup and view all the answers

    How many ATP are produced from the oxidation of 7 NADH molecules during the breakdown of palmitoyl CoA?

    <p>21 ATP</p> Signup and view all the answers

    What is the total energy yield from the oxidation of palmitoyl CoA after accounting for the activation energy?

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

    What key intermediate is produced during the breakdown of fatty acids with an odd number of carbons?

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

    What leads to a significant decrease in glucose levels in patients with MCAD deficiency?

    <p>Reduced ability to oxidize medium-chain fatty acids</p> Signup and view all the answers

    Which enzyme deficiency is particularly linked to sudden infant death syndrome (SIDS)?

    <p>MCAD enzyme</p> Signup and view all the answers

    In the context of beta oxidation of palmitoyl CoA, what is the significance of electron transport chain in yielding ATP?

    <p>FADH2 and NADH transfer electrons to the chain, producing ATP indirectly.</p> Signup and view all the answers

    Which enzyme catalyzes the transfer of the acyl group from CoA to carnitine?

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

    What compound inhibits the entry of long-chain acyl groups into the mitochondrial matrix?

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

    Which tissue contains about 97% of all carnitine in the body?

    <p>Skeletal muscle</p> Signup and view all the answers

    From which amino acids can carnitine be synthesized?

    <p>Lysine and methionine</p> Signup and view all the answers

    Which enzyme catalyzes the transfer of the acyl group from carnitine to CoA in the mitochondrial matrix?

    <p>Carnitine palmitoyltransferase II</p> Signup and view all the answers

    What is the role of carnitine-acylcarnitine translocase?

    <p>Transporting acylcarnitine into the mitochondrial matrix in exchange for free carnitine</p> Signup and view all the answers

    In which tissues can carnitine synthesis occur?

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

    Which factor decreases the CoA-requiring thiolase reaction during fatty acid oxidation?

    <p>Increasing acetyl CoA to CoA ratio</p> Signup and view all the answers

    What is a primary characteristic of secondary carnitine deficiency?

    <p>Often observed in patients undergoing hemodialysis</p> Signup and view all the answers

    Which condition is related to primary carnitine deficiency?

    <p>Issues with renal tubular reabsorption of carnitine</p> Signup and view all the answers

    How does genetic CPT-I deficiency primarily affect the body?

    <p>By impairing the liver's ability to synthesize glucose during fasting</p> Signup and view all the answers

    Which of the following is true about medium-chain fatty acids?

    <p>They are abundant in human milk</p> Signup and view all the answers

    What molecule is directly produced during the first oxidation step in beta-oxidation?

    <p>FADH2</p> Signup and view all the answers

    What is the net ATP yield from the complete oxidation of a palmitate molecule?

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

    Which step in beta-oxidation involves a thiolytic cleavage?

    <p>Final thiolytic cleavage</p> Signup and view all the answers

    What metabolic complication is NOT associated with CPT-II deficiency?

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

    What role does acetyl CoA play in linking fatty acid oxidation to gluconeogenesis?

    <p>It is a positive allosteric effector of pyruvate carboxylase</p> Signup and view all the answers

    What dietary modification is recommended for someone with carnitine deficiency?

    <p>High in carbohydrates and low in long-chain fatty acids</p> Signup and view all the answers

    Which enzyme is specifically required for the oxidation of monounsaturated fatty acids like 18:1(9) (oleic acid)?

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

    What is a product of the initial dehydrogenation in peroxisomes during the oxidation of very-long-chain fatty acids?

    <p>FADH2</p> Signup and view all the answers

    What is the side product formed when FADH2 is oxidized by molecular oxygen in the peroxisome?

    <p>H2O2</p> Signup and view all the answers

    Which disorder results from the inability to transport very-long-chain fatty acids across the peroxisomal membrane?

    <p>X-linked adrenoleukodystrophy</p> Signup and view all the answers

    What is the enzyme responsible for hydroxylating the α-carbon of phytanic acid in α-oxidation?

    <p>PhyH (phytanoyl CoA α-hydroxylase)</p> Signup and view all the answers

    What compound is produced when the initial carbon is released as CO2 during the α-oxidation of phytanic acid?

    <p>19-carbon pristanic acid</p> Signup and view all the answers

    Which enzyme deficiency causes Refsum disease?

    <p>PhyH (phytanoyl CoA α-hydroxylase)</p> Signup and view all the answers

    Liver mitochondria can convert acetyl CoA into which functional ketone bodies?

    <p>Acetoacetate and 3-hydroxybutyrate</p> Signup and view all the answers

    What happens to the energy output when oxidizing unsaturated fatty acids compared to saturated fatty acids?

    <p>Less energy is produced</p> Signup and view all the answers

    Which enzyme is required for the oxidation of polyunsaturated fatty acids such as 18:2(9,12) (linoleic acid) in addition to the isomerase?

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

    What activates Acetyl CoA carboxylase during fatty acid synthesis?

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

    Which component is NOT involved in fatty acid synthesis in the liver?

    <p>FADH2</p> Signup and view all the answers

    What compound inhibits carnitine palmitoyltransferase I, preventing fatty acid degradation in mitochondria?

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

    Where does the oxidation of very-long-chain fatty acids (VLCFA) primarily occur?

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

    Which enzyme deficiency leads to a common inborn error of metabolism causing hypoketonemia and hypoglycemia?

    <p>Medium-chain fatty acyl CoA dehydrogenase</p> Signup and view all the answers

    What role does the glycerol backbone from degraded triacylglycerol play in the liver?

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

    What enzyme is necessary for β-oxidation of fatty acids with an odd number of carbons to convert methylmalonyl CoA to succinyl CoA?

    <p>Methylmalonyl CoA mutase</p> Signup and view all the answers

    Which compound is an allosteric activator of Acetyl CoA carboxylase?

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

    In what cellular location does fatty acid desaturation occur?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    What is the primary regulator of the enzyme hormone-sensitive lipase in adipose tissue?

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

    Why are fatty acids considered important sources of energy for peripheral tissues?

    <p>They are soluble in aqueous solution and do not need to be transported as part of lipoproteins.</p> Signup and view all the answers

    What leads to the production of fatty acids in the liver?

    <p>Excess acetyl CoA beyond the liver's oxidative capacity</p> Signup and view all the answers

    Which enzyme's inhibition and activation are influenced by elevated hepatic acetyl CoA?

    <p>Pyruvate dehydrogenase and pyruvate carboxylase</p> Signup and view all the answers

    What allows for the continued oxidation of fatty acids during ketogenesis?

    <p>Generation of free CoA</p> Signup and view all the answers

    What determines the equilibrium between acetoacetate and 3-hydroxybutyrate?

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

    Which enzyme is the rate-limiting step in the synthesis of ketone bodies?

    <p>HMG CoA synthase</p> Signup and view all the answers

    Where is HMG CoA synthase primarily active?

    <p>In the liver</p> Signup and view all the answers

    What can acetoacetate spontaneously decarboxylate into?

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

    What happens to the NAD+/NADH ratio during fatty acid oxidation?

    <p>It decreases, pushing OAA to malate</p> Signup and view all the answers

    In the context of fatty acid oxidation disorders, what are the typical metabolic presentations?

    <p>Hypoketosis and hypoglycemia</p> Signup and view all the answers

    Which ketone body is produced through the reduction of acetoacetate?

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

    What is the initial substrate for ketone body synthesis in the liver?

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

    Which enzyme reduces acetoacetate to 3-hydroxybutyrate?

    <p>3-hydroxybutyrate dehydrogenase</p> Signup and view all the answers

    What condition results from the excessive accumulation of ketone bodies in the blood?

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

    Which of the following molecules is NOT a ketone body?

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

    What enzyme is responsible for converting acetoacetate to acetone?

    <p>Acetoacetate decarboxylase</p> Signup and view all the answers

    What initiates the synthesis of triacylglycerol in response to excess calorie intake?

    <p>Release of insulin</p> Signup and view all the answers

    What symptom is NOT typically associated with ketoacidosis?

    <p>Muscle cramps</p> Signup and view all the answers

    Which enzyme activity is associated with triacylglycerol degradation in a calorie-deficient diet?

    <p>Protein kinase</p> Signup and view all the answers

    Which enzyme transfers CoA from succinyl CoA to acetoacetate?

    <p>Succinyl CoA:acetoacetate CoA transferase</p> Signup and view all the answers

    What is the role of Malonyl CoA in the liver cytosol?

    <p>It is used to make C16 Fatty acyl CoA</p> Signup and view all the answers

    Which of the following is NOT a product of HMG-CoA breakdown?

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

    What happens to fatty acids in most tissues?

    <p>They are broken down by beta-oxidation to produce Acetyl CoA</p> Signup and view all the answers

    In diabetes mellitus, what primarily triggers the increased production of ketone bodies?

    <p>Lack of insulin</p> Signup and view all the answers

    What process occurs in the liver as a result of fatty acid breakdown?

    <p>Acetyl CoA can enter the TCA cycle or be converted to Acetoacetate</p> Signup and view all the answers

    Which hormone stimulates triacylglycerol synthesis?

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

    In patients with medium-chain fatty acyl CoA dehydrogenase (MCAD) deficiency, why does fasting hypoglycemia occur?

    <p>Impaired oxidation of fatty acids less than 12 carbons in length results in decreased production of acetyl CoA, the allosteric activator of pyruvate carboxylase, a gluconeogenic enzyme, thus, glucose levels fall.</p> Signup and view all the answers

    What is the specific defect in Zellweger syndrome that causes an accumulation of both very long chain fatty acids (VLCFA) and phytanic acid?

    <p>Inability to target matrix proteins to the peroxisome, thus all peroxisomal activities are affected.</p> Signup and view all the answers

    Which compound is expected to be radioactively labeled when industrial workers breathe air contaminated with ¹⁴C-labeled carbon dioxide?

    <p>About one third of the carbons of newly synthesized malonyl CoA.</p> Signup and view all the answers

    A teenager on a fat-free diet would be deficient in the synthesis of which lipid?

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

    Which of the following accurately depicts the defect in X-linked adrenoleukodystrophy (X-ALD)?

    <p>Inability to transport very long chain fatty acids (VLCFA) into the peroxisome.</p> Signup and view all the answers

    What is a common metabolic feature of Zellweger syndrome?

    <p>Accumulation of both VLCFA and phytanic acid</p> Signup and view all the answers

    Why are ketone bodies not found in the urine of patients with medium-chain fatty acyl CoA dehydrogenase (MCAD) deficiency during hypoglycemia?

    <p>Impaired fatty acid oxidation results in insufficient acetyl CoA production for ketogenesis.</p> Signup and view all the answers

    Why does a defect in fatty acid transport into peroxisomes result in the accumulation of very long chain fatty acids (VLCFA) in X-ALD?

    <p>Other cellular compartments lack enzymes for VLCFA degradation.</p> Signup and view all the answers

    Study Notes

    Synthesis and Degradation of Fatty Acids

    • Synthesis of Fatty Acids:
      • Occurs in the liver
      • Greatest flux through pathway: after a carbohydrate-rich meal
      • Hormonal state favoring pathway: high insulin/glucagon ratio
      • Major tissue site: liver
      • Subcellular location: cytosol
      • Carriers of acyl/acetyl groups between mitochondria and cytosol: citrate
      • Phosphopantetheine-containing active carriers: acyl carrier protein domain, coenzyme A
      • Oxidation/reduction coenzymes: NADPH
      • Two-carbon donor/product: malonyl CoA
      • Activator: citrate
      • Inhibitor: long-chain fatty acyl CoA
      • Product of pathway: palmitate

    Oxidation of Fatty Acids

    • Beta Oxidation:
      • Process yields 129 ATP total
      • Produces 7 FADH2 molecules, each providing 2 ATP when oxidized by CoQ of the electron transport chain, for a total of 14 ATP
      • Produces 7 NADH molecules, each providing 2 ATP when oxidized by NADH dehydrogenase, for a total of 21 ATP
      • Remaining 7 acetyl CoA molecules provide 12 ATP each when converted to CO2 and H2O by the TCA cycle, for a total of 96 ATP
      • Process requires 2 ATP to activate the palmitate to palmitoyl CoA, subtracted from the total
    • Medium-Chain Fatty Acyl CoA Dehydrogenase (MCAD) Deficiency:
      • A metabolic disorder caused by a deficiency in the MCAD enzyme
      • Occurs in 1:14,000 births worldwide
      • Causes a decrease in the ability to oxidize fatty acids with 6-10 carbons
      • Results in hypoglycemia and a build-up of fatty acids in the urine and blood
      • Treatment includes avoidance of fasting

    Oxidation of Unsaturated Fatty Acids

    • Unsaturated Fatty Acid Oxidation:
      • Provides less energy than saturated fatty acid oxidation
      • Requires an additional enzyme, 3,2-enoyl CoA isomerase, for monounsaturated fatty acids
      • Requires an NADPH-dependent 2,4-dienoyl CoA reductase for polyunsaturated fatty acids

    Ketone Bodies: An Alternate Fuel for Cells

    • Ketone Body Synthesis:
      • Occurs in the liver
      • Ketone bodies are produced from acetyl CoA derived from fatty acid oxidation
      • Compounds categorized as ketone bodies: acetoacetate, 3-hydroxybutyrate, and acetone
      • Acetoacetate can be reduced to form 3-hydroxybutyrate or decarboxylate to form acetone
    • Ketone Body Use by Peripheral Tissues:
      • Ketone bodies are used as an alternate fuel for cells
      • Produced in the liver and transported to peripheral tissues
      • Can be used by the brain to spare glucose during prolonged fasting

    Disorders of Fatty Acid Oxidation

    • Disorders of Fatty Acid Oxidation:
      • Present with hypoketosis and hypoglycemia
      • Caused by defects in fatty acid oxidation or transport
      • Symptoms include muscle weakness, hypoglycemia, and sudden infant death syndrome (SIDS)

    Excessive Production of Ketone Bodies in Diabetes Mellitus

    • Diabetic Ketoacidosis:
      • Caused by a lack of insulin
      • Leads to increased lipolysis and production of ketone bodies
      • Symptoms include fruity breath odor, rapid breathing, nausea, vomiting, abdominal pain, confusion, and coma
      • A medical emergency that can be life-threatening### Fatty Acid Metabolism
    • A fatty acid is a hydrocarbon chain with a terminal carboxyl group and can be saturated or unsaturated.
    • Linoleic and linolenic acids are essential for humans.

    Fatty Acid Synthesis

    • Occurs in the liver following a meal containing excess carbohydrate and protein.
    • Carbon required for synthesis is provided by acetyl CoA, energy is provided by ATP, and reducing equivalents by NADPH.
    • Citrate carries two-carbon acetyl units from the mitochondrial matrix to the cytosol.
    • The regulated step in fatty acid synthesis is catalyzed by Acetyl CoA carboxylase, which requires biotin.
    • Citrate is the allosteric activator of Acetyl CoA carboxylase, and long-chain fatty acyl CoA is the inhibitor.
    • The enzyme can be activated in the presence of insulin and inactivated by AMPK in response to epinephrine, glucagon, or a rise in AMP.

    Fatty Acid Elongation and Desaturation

    • Fatty acids can be elongated and desaturated in the ER.

    Triacylglycerol Synthesis and Degradation

    • Triacylglycerol synthesis occurs in response to ingestion of excess calories as carbohydrate, release of insulin, and protein phosphatase activity.
    • Triacylglycerol degradation occurs in response to calorie-deficient diet, release of glucagon, epinephrine, and protein kinase activity.

    Fatty Acid Degradation (β-Oxidation)

    • Occurs in mitochondria.
    • The carnitine shuttle is required to transport LCFA from the cytosol to the mitochondrial matrix.
    • A translocase and the enzymes carnitine palmitoyltransferases I and II are required.
    • Carnitine palmitoyltransferase I is inhibited by malonyl CoA.
    • Once in the mitochondria, fatty acids are oxidized, producing acetyl CoA, NADH, and FADH2.
    • The first step in the β-oxidation pathway is catalyzed by one of a family of four acyl CoA dehydrogenases, each of which has a specificity for either short-, medium-, long-, or very-long-chain fatty acids.

    Medium-Chain Acyl CoA Dehydrogenase (MCAD) Deficiency

    • Causes a decrease in fatty acid oxidation, resulting in hypoketonemia and severe hypoglycemia.

    Oxidation of Fatty Acids with an Odd Number of Carbons

    • Proceeds two carbons at a time, producing acetyl CoA until three carbons remain (propionyl CoA).
    • This compound is converted to methylmalonyl CoA (a reaction requiring biotin), which is then converted to succinyl CoA by methylmalonyl CoA mutase (requiring vitamin B12).

    Ketone Bodies

    • Liver mitochondria can convert acetyl CoA derived from fatty acid oxidation into the ketone bodies, acetoacetate and 3-hydroxybutyrate.
    • Peripheral tissues possessing mitochondria can oxidize 3-hydroxybutyrate to acetoacetate, which can be reconverted to acetyl CoA, thus producing energy for the cell.

    Triacylglycerol Synthesis and Degradation

    • Triacylglycerol synthesis occurs in the liver cytosol and ER.
    • Triacylglycerol degradation occurs in adipose tissue and liver.

    Regulation of Fatty Acid and Triacylglycerol Metabolism

    • Regulated by hormones and enzymes, such as insulin, glucagon, and epinephrine.
    • Insulin stimulates triacylglycerol synthesis, while glucagon and epinephrine stimulate triacylglycerol degradation.

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    Compare the synthesis and degradation of long-chain, even-numbered saturated fatty acids in this quiz. Test your knowledge of the pathways and processes involved.

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