Biochemistry II: Fatty Acid Metabolism Quiz
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Questions and Answers

What is the primary initial substrate used in the de novo synthesis of fatty acids?

  • Palmitate
  • Acetyl CoA (correct)
  • Glucose
  • Citrate

    • Which enzyme is considered the regulatory enzyme for fatty acid de novo synthesis?

  • Citrate lyase
  • Fatty acid synthase
  • Acetyl CoA carboxylase (correct)
  • NADPH oxidase

    • Where does the carboxylation of acetyl CoA to malonyl CoA occur?

  • In the nucleus
  • In the cytosol (correct)
  • In the mitochondria
  • In the endoplasmic reticulum

    • What is the final product of the de novo synthesis of fatty acids?

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

    Which pathway is primarily responsible for the transport of Acetyl CoA from the mitochondria to the cytosol?

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

    What is required along with Acetyl CoA for the synthesis of palmitate?

    <p>NADPH, CO2, ATP, and biotin</p> Signup and view all the answers

    How many malonyl CoA molecules are produced from seven Acetyl CoA during palmitate synthesis?

    <p>7</p> Signup and view all the answers

    What is the primary function of the carnitine shuttle?

    <p>Transport of long-chain fatty acyl CoA to the mitochondria</p> Signup and view all the answers

    Which enzyme is considered the regulatory enzyme of the carnitine shuttle?

    <p>Carnitine palmitoyl transferase-I (CPT-I)</p> Signup and view all the answers

    How many ATP molecules are yielded from each cycle of β-oxidation?

    <p>5 ATP</p> Signup and view all the answers

    What is the first step in the β-oxidation process of fatty acids?

    <p>Dehydrogenation (Oxidation)</p> Signup and view all the answers

    What inhibits the activity of carnitine palmitoyl transferase-I (CPT-I)?

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

    Which molecule acts as an allosteric activator for acetyl CoA carboxylase?

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

    What effect does glucagon have on acetyl CoA carboxylase activity?

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

    What is the main source of two-carbon units used in the elongation of palmitate?

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

    Which state is lipogenesis predominantly active?

    <p>Fed state</p> Signup and view all the answers

    Which enzyme is crucial for the conversion of free fatty acids into their activated form during lipogenesis?

    <p>FA thiokinase</p> Signup and view all the answers

    How does a high-calorie, high-carbohydrate diet affect acetyl CoA carboxylase synthesis?

    <p>Increases synthesis</p> Signup and view all the answers

    Which process involves the addition of cis double bonds to fatty acids?

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

    What is the role of NADPH in microsomal elongation?

    <p>Hydrogen donor</p> Signup and view all the answers

    Which of the following tissues can produce glycerol-3-P from both DHAP and glycerol?

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

    What is the role of hormone-sensitive lipase (HSL) in lipolysis?

    <p>It is the rate limiting step of lipolysis.</p> Signup and view all the answers

    Which substances activate hormone-sensitive lipase (HSL)?

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

    What happens to hormone-sensitive lipase (HSL) when insulin is present?

    <p>HSL is inhibited by dephosphorylation.</p> Signup and view all the answers

    Where does β-oxidation of fatty acids primarily occur?

    <p>In the mitochondrial matrix of most tissues.</p> Signup and view all the answers

    During which physiological state is fatty acid oxidation most active?

    <p>Fasting state.</p> Signup and view all the answers

    What occurs to free fatty acids during lipolysis?

    <p>They are transported in blood bound to albumin.</p> Signup and view all the answers

    Which enzyme is responsible for the activation of fatty acids to fatty acyl CoA?

    <p>Acyl CoA synthetase</p> Signup and view all the answers

    What is a characteristic of fatty acid oxidation in the brain?

    <p>It is limited due to low levels of FA degrading enzymes.</p> Signup and view all the answers

    Which pathway does lipolysis NOT influence?

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

    What is the fate of glycerol produced from lipolysis?

    <p>It enters gluconeogenesis.</p> Signup and view all the answers

    What is the primary function of lipolysis?

    <p>Mobilization of stored fats</p> Signup and view all the answers

    Which molecule serves as the initial substrate for lipolysis?

    <p>Triacylglycerol (TAG)</p> Signup and view all the answers

    In which tissue is lipolysis primarily taking place?

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

    What is the final product of lipolysis from one TAG molecule?

    <p>3 fatty acids and glycerol</p> Signup and view all the answers

    What is the energy yield from the oxidation of fats?

    <p>9 Kcal/g</p> Signup and view all the answers

    Where does the synthesis of triacylglycerol (TAG) take place in the body?

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

    Which fatty acid component is typically unsaturated in TAG?

    <p>R2</p> Signup and view all the answers

    What happens to TAG in the liver compared to adipose tissue?

    <p>TAG is packaged into VLDL in the liver</p> Signup and view all the answers

    What is the purpose of storing TAG in adipose tissue?

    <p>To serve as a depot for energy when needed</p> Signup and view all the answers

    Study Notes

    Biochemistry II (PB 503) - Fatty Acid, Triacylglycerol, and Ketone Body Metabolism

    • This course covers the metabolism of fatty acids, triacylglycerols, and ketone bodies.
    • The outline includes de novo synthesis of fatty acids, triacylglycerol synthesis, lipolysis, the carnitine shuttle, β-oxidation of fatty acids, oxidation of odd-chain fatty acids, ketogenesis, and ketolysis.

    I. Fatty Acid and Triacylglycerol Synthesis

    • De novo Synthesis of Fatty Acids:

      • Occurs in the fed state (stimulated by insulin).
      • Primary sites include liver and lactating mammary glands; also in adipose tissue to a lesser extent.
      • Location: cytosol.
      • Initial substrate: Acetyl CoA (derived from glucose).
      • Final product: Palmitic acid (palmitate).
      • Requirements: Acetyl CoA, NADPH, CO2, ATP, and biotin.

    • Steps of De Novo Synthesis:

      • Step 1: Transport of Acetyl CoA: Acetyl CoA from mitochondria is transported to cytosol via citrate shuttle. Citrate is a high-energy signal. High ATP and high citrate levels enhance the pathway.
      • Step 2: Carboxylation of Acetyl CoA: Acetyl CoA is carboxylated to malonyl CoA by acetyl CoA carboxylase (ACC). ACC is a regulatory enzyme.
      • Step 3: Palmitate Synthesis: Palmitate is synthesized by fatty acid synthase multienzyme complex. 8 acetyl CoA molecules are needed.

    • Major Sources of NADPH:

      • HMP shunt (pentose phosphate pathway): Each glucose molecule entering this pathway yields 2 NADPH.H+.
      • Cytosolic malate to pyruvate conversion (by malic enzyme).
      • Cytosolic isocitrate dehydrogenase.

    • Regulation of FA Synthesis:

      • Allosteric Regulation: Citrate activates and palmitoyl CoA inhibits acetyl-CoA carboxylase (ACC).
      • Covalent Modification: Insulin dephosphorylates ACC, activating it and thus increasing FA synthesis. Glucagon and epinephrine phosphorylate ACC, inactivating it and thus decreasing FA synthesis. This is a short-term regulation.
      • Hormonal Regulation: Long-term regulation of FA synthesis: Prolonged high-calorie/high-CHO/low-fat diet increases acetyl CoA carboxylase syntheses. Conversely low calorie/low CHO or high fat diet decreases FA synthesis.

    II. Fatty Acid and Triacylglycerol Degradation (Lipolysis)

    • Lipolysis:

      • Mobilization of stored fats (triacylglycerols or TAGs) in adipose tissue.
      • Occurs as a response to the fasting state.
      • Takes place in the cytosol of adipose tissue.
      • Initial substrate: TAG.
      • Final products: 3 fatty acids and glycerol (for energy production).
      • Note: The energy yield from fat oxidation is 9 Kcal/g compared to 4 Kcal/g for protein and carbohydrate.

    • Steps of Lipolysis:

      • Hormone-sensitive lipase (HSL) breaks down TAGs into diglycerides, monoglycerides, and free fatty acids(FFAs)
      • Diglyceride Lipase (HSL) and Monoacylglycerol Lipase (MGL) continues break down to glycerol and FFAs.
      • Regulation: Hormone-sensitive lipase (HSL) is the rate-limiting step. HSL is activated when phosphorylated by PKA in response to glucagon and epinephrine, and inactivated by dephosphorylation when stimulated by insulin.

    III. Fate of Glycerol and Free FAs

    • Glycerol can be used for gluconeogenesis.
    • Fatty acids (FFAs) are transported in the blood bound to albumin and are used for β-oxidation.

    IV. β-Oxidation of Fatty Acids

    • This is the primary process of fatty acid oxidation.
    • Occurs in the mitochondrial matrix of most tissues.
    • Fatty acid is first activated to fatty acyl CoA and then transported into the mitochondria. This requires carnitine shuttle for long-chain FAs.
    • The cycle involves four steps: Oxidation, Hydration, Oxidation, Thiolysis.
    • Each cycle shortens the fatty acyl CoA by 2 carbons and yields 1 FADH2, 1 NADH, and 1 acetyl CoA.
    • Calculation of the energy yield considers the acetyl CoA molecules, number of cycles and ATP yield from each cycle. The total ATP yield is significantly greater than the ATP required for fatty acid activation.

    V. Oxidation of Odd-Chain Fatty Acids

    • Proceeds through beta-oxidation as even chain FAs.
    • Eventually produces propionyl CoA, which is metabolized into succinyl CoA and utilized in the TCA cycle.

    VI. Ketogenesis

    • Overview:
      • Occurs in the liver in response to prolonged fasting/starvation.
      • Location: mitochondrial matrix of the liver.
      • Initial substrate: excess acetyl CoA from fatty acid oxidation.
      • Final product: 3 ketone bodies (acetoacetate, β-hydroxybutyrate, acetone).
    • Steps:
      • Acetoacetyl CoA combines with acetyl CoA.
      • HMG-CoA synthase is the rate-limiting enzyme.
      • Acetoacetate is reduced to β-hydroxybutyrate.
      • Acetone can be released from acetoacetate.

    VII. Ketolysis

    • Overview:
      • Occurs in the mitochondrial matrix of extrahepatic tissues (brain, kidneys, hearts, etc.) during prolonged fasting/starvation or other conditions where glucose is not available or insufficient.
      • In these tissues, ketone bodies are the primary energy source.
    • Steps:
      • Ketone bodies are converted into acetyl CoA.
      • Acetyl CoA enters the TCA cycle, providing energy.

    VIII. Ketone Bodies and Uncontrolled Diabetes Mellitus

    • Diabetic ketoacidosis (DKA):
      • Characterized by elevated ketone bodies in the blood (ketonemia) and urine (ketonuria).
      • Results from insufficient insulin, increasing lipolysis and subsequent ketogenesis.
      • Fruity odor on the breath due to increased acetone.

    IX. Cholesterol Synthesis versus Ketogenesis

    • The initial steps of cholesterol synthesis and ketogenesis share some reactions (steps 1 and 2), but their subsequent fates differ. HMG-CoA is a key branching point. The pathways differ in location and rate-limiting steps.

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    Lec 8,9 Biochemistry II Fatty Acids, Triacylglycerol & Ketone Bodies PDF

    Description

    Test your knowledge on the metabolism of fatty acids, triacylglycerols, and ketone bodies as covered in Biochemistry II (PB 503). This quiz includes questions on key processes such as de novo synthesis, β-oxidation, and the role of insulin in metabolism. Challenge yourself and reinforce your understanding of these vital biochemical pathways.

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