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Biochemistry of Lipid Metabolism
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Biochemistry of Lipid Metabolism

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Questions and Answers

What percentage of fatty acids undergo beta-oxidation in the liver?

  • 95
  • 85
  • 80 (correct)
  • 90
  • What is the name of the lipoprotein that has a very low density?

  • HDL
  • LDL
  • VLDL (correct)
  • IDL
  • Where does citrate play a role in the regulation of fatty acid synthesis?

  • Golgi apparatus
  • Cytoplasm
  • Endoplasmic reticulum
  • Mitochondria (correct)
  • What is the name of the process by which glycogen is converted to glucose?

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

    What is the name of the molecule that is involved in the transport of fatty acids into the mitochondria?

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

    What is the role of UDP glucose pyrophosphorylase in glycogen synthesis?

    <p>To synthesize glycogen from glucose-1-phosphate and UTP</p> Signup and view all the answers

    What is the function of glycogenin in glycogen synthesis?

    <p>To create a glycogen primer molecule</p> Signup and view all the answers

    What type of bond is formed between glucose residues in a glycogen primer?

    <p>Alpha-1,4 glycosidic bond</p> Signup and view all the answers

    What is the role of glycogen synthase in glycogen synthesis?

    <p>To add glucose units to a glycogen primer molecule</p> Signup and view all the answers

    Why is a branching enzyme necessary in glycogen synthesis?

    <p>To create alpha-1,6 linkages between glucose units</p> Signup and view all the answers

    What is the minimum number of glucose residues required for branching to occur in glycogen synthesis?

    <p>11-12 glucose residues</p> Signup and view all the answers

    What is the result of the branching enzyme's action in glycogen synthesis?

    <p>A block of 7 glucose residues is transferred to another site</p> Signup and view all the answers

    What is the linkage formed between glucose units added by glycogen synthase?

    <p>Alpha-1,4 glycosidic bond</p> Signup and view all the answers

    What is the structure of glycogenin?

    <p>A protein-carbohydrate complex</p> Signup and view all the answers

    What is the role of UDP-glucose in glycogen synthesis?

    <p>To synthesize glycogen from glucose-1-phosphate and UTP</p> Signup and view all the answers

    Study Notes

    Non-Carbohydrate Precursors of Glucose

    • Amino acid catabolism is the main source of pyruvate and oxaloacetate for gluconeogenesis during fasting or carbohydrate starvation.
    • Muscle proteins break down to supply amino acids, which are transported to the liver and deaminated to gluconeogenesis inputs.
    • Glycerol, derived from hydrolysis of triacylglycerols in fat cells, is also a significant input to gluconeogenesis.

    Bypass of Irreversible Steps in Glycolysis

    • In gluconeogenesis, three reactions are bypassed by a set of separate enzymes.
    • The bypass of pyruvate kinase involves two enzymes: pyruvate phosphoenoenolpyruvate and phosphoenolpyruvate carboxy kinase.
    • Carboxylation occurs in the mitochondria, where pyruvate is converted to oxaloacetate by pyruvate carboxylase, requiring biotin and ATP.
    • The oxaloacetate is then transported from the mitochondria to the cytosol using the malate-aspartate shuttle.

    Conversion of Oxaloacetate to Glucose

    • Oxaloacetate is converted to 3-phosphoglycerate, which is then converted to glyceraldehyde-3-phosphate.
    • Two molecules of glyceraldehyde-3-phosphate combine to form fructose-1,6-bisphosphate, which is then converted to fructose-6-phosphate and glucose-6-phosphate.
    • Glucose-6-phosphate is isomerized to glucose-6-phosphate by phosphohexo isomerase.
    • Glucose-6-phosphate is hydrolyzed to free glucose by glucose-6-phosphatase, mainly in the liver.

    Significance of Gluconeogenesis

    • Only the liver can replenish blood glucose through gluconeogenesis, maintaining blood glucose levels.
    • Gluconeogenesis maintains blood glucose levels during starvation, when glycogen stores are depleted.
    • The process requires energy, with 6 ATPs required to generate one glucose molecule.
    • Hormones like glucagon and glucocorticoids increase gluconeogenesis, while insulin inhibits it.

    Glycogen Metabolism

    • Glycogen is a highly branched glucose polymer, stored in the liver and muscle.
    • Liver glycogen provides glucose during fasting, while muscle glycogen acts as a reserve fuel for muscle contraction.
    • Glycogen degradation (glycogenolysis) involves phosphorolysis, debranching, and glycogen phosphorylase.

    Glycogen Synthesis and Degradation

    • Glycogen synthesis involves glycogenin, UDP glucose, and glycogen synthase.
    • Glycogen degradation involves glycogen phosphorylase, debranching enzymes, and glycogen synthase.
    • Regulation of glycogen metabolism involves carbohydrates, fatty acids, protein, and hormonal balance.

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    Description

    This quiz covers the biochemistry of lipid metabolism, including the role of the liver, glycogenesis, lipogenesis, beta-oxidation, and the regulation of ketone production. It also touches on the density of lipoproteins and their function.

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