Biochemistry of Ketone Bodies and Cholesterol
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Questions and Answers

What is the yield of ATP from the oxidation of β-hydroxybutyrate?

  • 22 ATP
  • 19 ATP
  • 21.5 ATP (correct)
  • 17 ATP

    • Which factor primarily regulates ketolysis?

  • Availability of fatty acids
  • Availability of oxaloacetate (correct)
  • Insulin levels
  • Glucose concentration

    • What adaptation occurs in the brain during starvation after 5-6 days?

  • Increased fatty acid oxidation
  • Increased glucose utilization
  • Adaptation to using ketone bodies (correct)
  • Decreased energy requirements

    • Which condition is NOT a cause of ketosis?

    <p>High glucose intake</p> Signup and view all the answers

    What is the normal range of ketone bodies in blood?

    <p>0.5-3 mg/dL</p> Signup and view all the answers

    What is the key enzyme involved in cholesterol synthesis?

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

    What happens to HMG-CoA reductase when insulin is present?

    <p>It is induced and dephosphorylated.</p> Signup and view all the answers

    Which hormone acts as a repressor of HMG-CoA reductase?

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

    During periods of low energy availability, cholesterol synthesis is affected how?

    <p>Cholesterol synthesis decreases.</p> Signup and view all the answers

    What mechanism do statins use to lower plasma cholesterol?

    <p>Competing with HMG-CoA for reductase binding.</p> Signup and view all the answers

    What is the primary enzyme responsible for synthesizing glycerol-3-phosphate in the liver and kidneys?

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

    Which tissue synthesizes glycerol-3-phosphate by reducing dihydroxyacetone phosphate (DHAP)?

    <p>Adipose tissue</p> Signup and view all the answers

    What is the first product formed when glycerol-3-phosphate condenses with two acyl-CoA molecules?

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

    Which enzyme is involved in removing phosphate from phosphatidic acid to form diacylglycerol?

    <p>PPH-1</p> Signup and view all the answers

    What final product is produced after the esterification of diacylglycerol with an additional acyl-CoA molecule?

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

    What is the active form of Acetyl-CoA Carboxylase (ACC)?

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

    Which of the following hormones is responsible for inhibiting lipogenesis?

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

    Which carbon source is used by the microsomal system for fatty acid elongation?

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

    What is the role of cholesterol in the formation of cell membranes?

    <p>Cholesterol regulates membrane fluidity.</p> Signup and view all the answers

    What distinguishes the microsomal system for fatty acid elongation from de novo synthesis?

    <p>It cannot initiate de novo synthesis</p> Signup and view all the answers

    How is vitamin D3 synthesized from cholesterol?

    <p>By dehydrogenation of cholesterol followed by UV radiation.</p> Signup and view all the answers

    Which of the following fatty acids cannot be synthesized by the body?

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

    What are the steroid hormones derived from cholesterol?

    <p>Androgens, estrogens, progesterone, and corticoids.</p> Signup and view all the answers

    What proportion of cholesterol in plasma is present as cholesteryl esters?

    <p>2/3</p> Signup and view all the answers

    Which of the following is NOT a function of cholesterol?

    <p>Storage of carbohydrates.</p> Signup and view all the answers

    What is the primary cause of Refsum's Disease?

    <p>Deficiency of α-hydroxylase</p> Signup and view all the answers

    In which tissues does phytanic acid accumulate due to a deficiency of α-hydroxylase?

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

    Which systems are responsible for fatty acid synthesis?

    <p>Cytosolic system and microsomal system</p> Signup and view all the answers

    What is the initial substrate used for de novo fatty acid synthesis?

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

    Where does the cytosolic system for de novo fatty acid synthesis primarily occur?

    <p>Liver and lactating mammary gland</p> Signup and view all the answers

    What occurs as a result of increased lipolysis during ketogenesis?

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

    Where does ketolysis primarily occur?

    <p>In the mitochondria of extrahepatic tissues</p> Signup and view all the answers

    What is the primary consequence of increased ketogenesis in ketosis?

    <p>Production of acetoacetate and β-hydroxybutyrate</p> Signup and view all the answers

    What is the role of succinyl-CoA in the process of ketolysis?

    <p>It is necessary for the thiophorase reaction</p> Signup and view all the answers

    Which of the following substances is considered anti-ketogenic?

    <p>Glucogenic amino acids</p> Signup and view all the answers

    Which molecule is produced from the conversion of β-hydroxybutyrate during ketolysis?

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

    What is the maximum level of ketonemia considered physiological during a ketogenic diet?

    <p>140 mg/dL</p> Signup and view all the answers

    What happens to the Krebs cycle during increased ATP production from ketogenesis?

    <p>It becomes less active</p> Signup and view all the answers

    What is one of the main objectives of administering IV glucose during the management of ketosis?

    <p>To help lower blood sugar levels</p> Signup and view all the answers

    What happens to acetyl CoA when oxaloacetate is absent and ATP levels are high?

    <p>It is used for ketone body synthesis</p> Signup and view all the answers

    What is the initial substrate that combines with oxaloacetate to form citrate in the mitochondria?

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

    Which enzyme converts citrate back into oxaloacetate and acetyl-CoA in the cytosol?

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

    How many acetyl-CoA molecules are required for the synthesis of palmitic acid?

    <p>8</p> Signup and view all the answers

    Which of the following statements is true about malonyl-CoA?

    <p>Malonyl-CoA inhibits carnitine palmitoyltransferase I.</p> Signup and view all the answers

    What is one source of NADPH used in fatty acid synthesis in the cytosol?

    <p>Pentose Phosphate Pathway</p> Signup and view all the answers

    What is the primary source of acetyl CoA for ketogenesis?

    <p>Oxidation of fatty acids</p> Signup and view all the answers

    What is the first step in the ketogenesis process?

    <p>Conversion of Acetyl-CoA to Acetoacetyl-CoA</p> Signup and view all the answers

    Where does ketogenesis primarily occur in the body?

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

    Which enzyme is responsible for the conversion of HMG-CoA to Acetoacetate?

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

    What is the terminal product of β-hydroxybutyrate oxidation?

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

    Which ketone body is produced from the spontaneous conversion of Acetoacetate?

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

    Which substrate is required for the conversion of Acetoacetate to β-hydroxybutyrate?

    <p>NADH+H^+</p> Signup and view all the answers

    Which of the following is NOT a ketone body produced during ketogenesis?

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

    Study Notes

    Regulation of Cholesterol Synthesis

    • Key enzyme: HMG-CoA reductase is the rate-limiting reaction
    • Enzyme activity is controlled by reversible phosphorylation/dephosphorylation.
      • The active form (a) is dephosphorylated
      • Phosphorylation is catalyzed by AMP-activated protein kinase (AMPK).

    1. Hormonal Regulation

    • Feeding and insulin

      • Insulin stimulates cholesterol synthesis
      • Insulin acts as an inducer for HMG-CoA reductase gene
      • Activates protein phosphatase which catalyze dephosphorylation of HMGCoA reductase

    • Fasting and glucagon

      • Glucagon acts as a repressor for HMGCoA reductase.

    2. Allosteric Regulation

    • Cholesterol is a group of drugs that act through competitive inhibition of HMG-CoA reductase (structural analogs to HMG-CoA) and help to lower plasma cholesterol.
      • Statins are a group of drugs that act through competitive inhibition of HMG-CoA reductase (structural analogs to HMG-CoA) and help to lower plasma cholesterol

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    Description

    This quiz explores key concepts related to ketone bodies and cholesterol synthesis, including the regulation of ketolysis and the adaptation of the brain during starvation. It covers enzymatic pathways and hormonal influences on lipid metabolism. Test your knowledge on the biochemical processes critical to energy regulation in the body.

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