Medical Biochemistry - Lipid Metabolism
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Questions and Answers

What role does malate dehydrogenase play in the biosynthesis of fatty acids?

  • It converts pyruvate to oxaloacetate.
  • It catalyzes the esterification of fatty acids.
  • It produces NADPH from malate.
  • It converts oxaloacetate to malate. (correct)
  • How is triacylglycerol formed?

  • From the conversion of glucose to glycerol.
  • By the conversion of pyruvate to fatty acids.
  • By the reaction of NADPH with malate.
  • Through the esterification of fatty acids with glycerol-3 phosphate. (correct)
  • What is the primary source of NADPH in fatty acid synthesis?

  • Conversion of fatty acids into TAG.
  • Lipolysis of depot fat.
  • Malic enzyme and the pentose phosphate pathway. (correct)
  • Insulin stimulation of glycolysis.
  • What is the primary effect of insulin on lipogenesis?

    <p>Stimulates lipogenesis by promoting glucose uptake.</p> Signup and view all the answers

    What happens to the TAG formed in the liver?

    <p>It is transformed into VLDL and distributed to tissues.</p> Signup and view all the answers

    What is the primary function of chylomicrons?

    <p>Transport dietary lipids</p> Signup and view all the answers

    Which apolipoprotein is associated with the receptor binding of VLDL?

    <p>Apo B-100</p> Signup and view all the answers

    What happens to VLDL as it loses triglycerides in the bloodstream?

    <p>It is converted to LDL</p> Signup and view all the answers

    Which of the following lipoproteins carries approximately 50% of blood cholesterol?

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

    Hyperlipoproteinemia is characterized by what?

    <p>Increased plasma lipoproteins</p> Signup and view all the answers

    What is a characteristic feature of Hyperlipidemia Type II?

    <p>Reduced LDL metabolism</p> Signup and view all the answers

    What is the role of apo E in lipoprotein metabolism?

    <p>Required for VLDL and chylomicron metabolism</p> Signup and view all the answers

    Which type of hyperlipidemia is characterized by both hypercholesterolemia and hypertriacylglycerodemia?

    <p>Type III</p> Signup and view all the answers

    What characterizes Type V hyperlipoproteinemia?

    <p>Increased levels of chylomicrons and VLDL</p> Signup and view all the answers

    Which process is primarily responsible for lipogenesis in mammals?

    <p>Fatty acid biosynthesis</p> Signup and view all the answers

    What is the main stored form of energy in adipose cells?

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

    What role does glycerol-3 phosphate dehydrogenase play in lipid metabolism?

    <p>Reduces dihydroxy acetone phosphate to glycerol-3 phosphate</p> Signup and view all the answers

    Which of the following is a requirement for the de novo synthesis of fatty acids?

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

    In which organ is glycerokinase present, allowing glycerol phosphate formation from glucose?

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

    Which cofactor is NOT required for lipogenesis?

    <p>Coenzyme A</p> Signup and view all the answers

    What effect does uncontrolled diabetes have on lipid metabolism?

    <p>Accumulation of triacylglycerols in the liver</p> Signup and view all the answers

    What is the primary function of apolipoproteins?

    <p>To combine and transport lipids</p> Signup and view all the answers

    Which lipoprotein is primarily responsible for transporting dietary lipids from the intestine to tissues?

    <p>Chylomicrons (CM)</p> Signup and view all the answers

    Which of the following lipoproteins carries cholesterol esters as its major lipid component?

    <p>High density lipoprotein (HDL)</p> Signup and view all the answers

    Apo-A1 is a major apolipoprotein for which type of lipoprotein?

    <p>High density lipoprotein (HDL)</p> Signup and view all the answers

    Which of the following statements about lipoproteins is true?

    <p>Triglycerides are found in the core of lipoproteins.</p> Signup and view all the answers

    What is the ligand for LDL receptors?

    <p>Apo-B 100</p> Signup and view all the answers

    Which lipoprotein is involved in transferring endogenous lipids from the liver to peripheral tissues?

    <p>Very low density lipoprotein (VLDL)</p> Signup and view all the answers

    Which apolipoprotein activates lipoprotein lipase?

    <p>Apo-C II</p> Signup and view all the answers

    What is formed from the condensation of acetyl-CoA and oxaloacetate for transport out of mitochondria?

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

    Which enzyme is responsible for converting acetyl-CoA to malonyl-CoA in fatty acid synthesis?

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

    What is the final product of fatty acid synthesis as mentioned in the process?

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

    How many molecules of NADPH are consumed in the overall reaction of fatty acid synthesis?

    <p>14</p> Signup and view all the answers

    Which step involves the repetition of four distinct reactions leading to fatty acid elongation?

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

    What is the primary role of ATP in the fatty acid synthesis process?

    <p>To convert acetyl-CoA to malonyl-CoA</p> Signup and view all the answers

    What molecule is NOT produced during the synthesis of palmitate?

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

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

    <p>It is the main building block for fatty acid synthesis.</p> Signup and view all the answers

    Study Notes

    Medical Biochemistry - Lipid Metabolism

    • This course covers lipid transport, biosynthesis, and associated disorders, specifically for first-year MBBS and Dentistry students at Umm Al-qura University.

    Lipid Transport

    • Lipids in blood plasma, including fats, phospholipids, cholesterol, cholesterol esters, and fatty acids, are transported as lipoproteins.
    • Lipoproteins are non-covalent assemblies of lipids and proteins.
    • Key lipoprotein types include chylomicrons, VLDL, LDL, and HDL, each with unique structural components (core and surface) and functions in transporting triglycerides and cholesterol throughout the body.

    Lipoprotein Composition

    • Key proteins (apoproteins): Apo B-48, Apo B-100, and Apo A-I.
    • Key lipids (lipoproteins) include TG, TG, CE, CE.
    • Different lipoproteins have varying percentages of protein and lipid content.

    Lipoprotein Disorders

    • Hyperlipoproteinemia (hyperlipidemia): A group of disorders characterized by elevated plasma lipoprotein levels.
    • Hyperlipidemia is classified into five types (Type I to Type V), each with a specific cause and manifestation.
    • Type I: Deficiency in lipoprotein lipase enzyme resulting in increased plasma chylomicrons and turbid plasma.
    • Type II: Reduced LDL metabolism due to LDL receptor defects, leading to high plasma cholesterol levels (familial hypercholesterolemia).
    • Type III: Defective Apo E, affecting uptake and metabolism of VLDL and chylomicron remnants, resulting in both high cholesterol and high triglycerides.
    • Type IV: Increased formation of triglycerides from carbohydrates, leading to high VLDL and triglycerides levels, and turbid plasma.
    • Type V: Associated with obesity and glucose intolerance, featuring high chylomicrons, high VLDL, and high triglycerides, and turbid plasma.

    Fatty Liver

    • Fatty liver is a metabolic disorder where triglycerides accumulate in the liver.
    • This can occur during fasting, high-fat diets, or uncontrolled diabetes.

    Lipid Biosynthesis

    • This section focuses on the synthesis of lipids, specifically fatty acids.
    • It details the biosynthesis process, highlighting the key regulatory enzymes and steps.

    Fatty Acid Synthesis (Lipogenesis)

    • Lipogenesis primarily occurs in the liver and adipose tissues, but also in other organs like brain and kidneys.
    • It utilizes acetyl-CoA as the key substrate and requires cofactors such as NADPH, ATP, Mn2+, biotin, and HCO3-.
    • Fatty acid synthesis is a separate metabolic pathway distinct from fatty acid breakdown.
    • A crucial step involves the formation of citrate from acetyl-CoA within the mitochondria, followed by citrate translocation to the cytoplasm. The citric acid cycle plays a part of acetyl-CoA conversion into fatty acids.

    Synthesis of Glycerol-3P

    • Glucose is oxidized via glycolysis to dihydroxyacetone phosphate.
    • This is reduced to glycerol-3 phosphate by the enzyme glycerol-3 phosphate dehydrogenase, making glycerol-3-P the precursor for membrane lipids and triglycerides.

    Regulation of Lipogenesis

    • Insulin promotes lipogenesis, while glucagon and epinephrine inhibit it.
    • Insulin affects short-term regulation of acetyl CoA carboxylase (a regulatory enzyme in fatty acid synthesis).
    • Long-term regulation may also be affected by diet, such as high/low carbohydrate intake.

    Fates of Formed TAG

    • Formed TAG (triacylglycerol) is transported differently after its formation.
    • In the liver, TAG is initially converted into VLDL for transport to tissues.
    • In adipose tissue, TAG is stored as fat.

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    Description

    This quiz focuses on lipid metabolism, including lipid transport, biosynthesis, and associated disorders. Specifically designed for first-year MBBS and Dentistry students, it covers essential details about lipoprotein types, their composition, and related disorders. Test your knowledge on key concepts and functions of lipoproteins in the human body.

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