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Phosphorylation of Glucose
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Phosphorylation of Glucose

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@VeritableJadeite

Questions and Answers

What is the primary purpose of phosphorylating glucose in the cell?

  • To effectively trap glucose as glucose 6-phosphate (correct)
  • To allow glucose to diffuse out of the cell
  • To promote the oxidation of pyruvate
  • To release glucose into the bloodstream

    • How does the phosphorylation of glucose affect ATP production?

  • It has no impact on ATP production
  • It produces 2 moles ATP per mole of glucose
  • It produces 6 moles ATP per mole of glucose (correct)
  • It reduces the amount of ATP produced

    • Which enzyme is primarily responsible for the phosphorylation of glucose in most tissues?

  • Hexokinase I (correct)
  • Pyruvate kinase
  • Phosphofructokinase
  • Glucose-6-phosphate dehydrogenase

    • What is a consequence of the lack of specific carriers for phosphorylated sugars?

    <p>Phosphorylated sugars do not readily penetrate cell membranes</p> Signup and view all the answers

    What role does oxygen play in the process mentioned in the context of glucose phosphorylation?

    <p>It reoxidizes NADH formed during glucose oxidation</p> Signup and view all the answers

    What happens during the conversion of hexose to triose phosphate in glycolysis?

    <p>A 6-carbon sugar is converted into two 3-carbon sugars</p> Signup and view all the answers

    What is a key characteristic of glucose 6-phosphate after phosphorylation?

    <p>It is too polar to diffuse out of the cell</p> Signup and view all the answers

    Which statement about the ATP requirements during the conversion of hexose to triose phosphate is accurate?

    <p>Two moles of ATP are required per mole of hexose</p> Signup and view all the answers

    What is a significant outcome of the oxidative decarboxylation of pyruvate?

    <p>It produces acetyl CoA which enters the citric acid cycle</p> Signup and view all the answers

    What is the most common cause of enzyme deficiency-related hemolytic anemia?

    <p>Glucose 6-Phosphate Dehydrogenase Deficiency</p> Signup and view all the answers

    What blood lactate level is indicative of lactic acidosis?

    <p>5.0 mM</p> Signup and view all the answers

    What effect does hormonal regulation have on enzyme activity compared to short-term regulation?

    <p>Hormonal regulation has a more profound but slower effect.</p> Signup and view all the answers

    Why do mature red blood cells (RBCs) rely entirely on glycolysis for ATP production?

    <p>They completely lack mitochondria.</p> Signup and view all the answers

    Which process can lead to lactic acidosis?

    <p>Inadequate oxygen availability during high energy demand.</p> Signup and view all the answers

    What is the role of phosphorylation or dephosphorylation in glycolysis regulation?

    <p>It modifies rate-limiting enzymes for immediate regulation.</p> Signup and view all the answers

    What is the primary function of phosphofructokinase 1 (PFK-1) in glycolysis?

    <p>Catalyzes the phosphorylation of fructose 6-phosphate</p> Signup and view all the answers

    Which of the following statements is true regarding the isomerization of glucose 6-phosphate?

    <p>It is catalyzed by phosphoglucose isomerase</p> Signup and view all the answers

    What role does ATP play in the phosphorylation of fructose 6-phosphate?

    <p>Inhibits the activity of phosphofructokinase 1</p> Signup and view all the answers

    Which enzyme catalyzes the cleavage of fructose 1,6-bisphosphate?

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

    In which tissues is the oxidative decarboxylation of pyruvate particularly important?

    <p>Cardiac muscle tissues</p> Signup and view all the answers

    What is the fate of pyruvate in the process of oxidative decarboxylation?

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

    What is the main regulatory factor for phosphofructokinase 1 activity?

    <p>Concentration of ATP and other modulators</p> Signup and view all the answers

    Which reaction catalyzed by the pyruvate dehydrogenase complex is crucial for energy metabolism?

    <p>Conversion of pyruvate to acetyl CoA</p> Signup and view all the answers

    What type of reaction is the cleavage of fructose 1,6-bisphosphate classified as?

    <p>Reversible and unregulated</p> Signup and view all the answers

    How does aldolase function in the metabolism of dietary fructose?

    <p>By cleaving fructose 1,6-bisphosphate</p> Signup and view all the answers

    What is the main function of pyruvate carboxylase in DHAP isomerization?

    <p>Interconverts DHAP and glyceraldehyde 3-phosphate</p> Signup and view all the answers

    Which of the following molecules is produced from the isomerization of DHAP?

    <p>2 molecules of glyceraldehyde 3-phosphate</p> Signup and view all the answers

    What role does NAD+ play in glycolysis?

    <p>It serves as an electron carrier during the oxidation of glyceraldehyde 3-phosphate.</p> Signup and view all the answers

    Which of the following statements about anaerobic glycolysis is true?

    <p>Lactate is the primary end product.</p> Signup and view all the answers

    What happens to pyruvate during the reduction to lactate?

    <p>It is reduced to form lactate in the absence of oxygen.</p> Signup and view all the answers

    Which enzyme catalyzes the reaction of pyruvate to alanine?

    <p>Alanine aminotransferase</p> Signup and view all the answers

    How many ATP molecules are produced from anaerobic glycolysis per glucose molecule?

    <p>2 molecules of ATP</p> Signup and view all the answers

    In which process does pyruvate decarboxylase participate?

    <p>Reduction of pyruvate to ethanol</p> Signup and view all the answers

    What is the primary role of glyceraldehyde 3-phosphate oxidation in glycolysis?

    <p>To generate ATP and NADH</p> Signup and view all the answers

    What characterizes the energy yield of aerobic glycolysis compared to anaerobic glycolysis?

    <p>Higher ATP yield per glucose molecule</p> Signup and view all the answers

    What is the role of phosphoglycerate kinase in the glycolytic pathway?

    <p>Facilitates the conversion of 1,3-BPG to 3-PG</p> Signup and view all the answers

    Why does the liver require a high Km for glucose in certain conditions?

    <p>To ensure that insulin secretion occurs primarily when blood glucose is high</p> Signup and view all the answers

    Which enzyme catalyzes the shift of a phosphate group from carbon 3 to carbon 2?

    <p>Phosphoglycerate mutase</p> Signup and view all the answers

    What does the GLUT-2 transporter primarily facilitate?

    <p>Equilibration of blood glucose concentration across hepatocyte membranes</p> Signup and view all the answers

    What effect does a carbohydrate-rich diet have on glucose phosphorylation?

    <p>Enhances insulin secretion and glucose sensor activation</p> Signup and view all the answers

    Which of the following statements about pyruvate formation is true?

    <p>It occurs after the dehydration of 2-phosphoglycerate</p> Signup and view all the answers

    Which compound is required for the conversion of 1,3-BPG into 3-PG?

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

    What is the primary function of the lactate dehydrogenase enzyme in glycolysis?

    <p>Converts pyruvate to lactate under anaerobic conditions</p> Signup and view all the answers

    What is the role of fructose-6-phosphate in glucose metabolism?

    <p>Regulates the activity of key enzymes in glycolysis</p> Signup and view all the answers

    Which statement accurately describes the process of minimizing hyperglycemia during the absorptive period?

    <p>The high Vmax of GLUT-2 helps efficiently remove glucose.</p> Signup and view all the answers

    Study Notes

    Phosphorylation of Glucose

    • Requires oxygen to reoxidize NADH produced during glyceraldehyde 3-phosphate oxidation.
    • Irreversible process, effectively trapping glucose as glucose 6-phosphate, which is too polar to diffuse out of the cell.
    • Produces 6 moles of ATP per mole of glucose.

    Stages of Glycolysis

    • Conversion of Hexose to Triose Phosphate
      • 6-carbon sugar is cleaved into two 3-carbon sugars.
      • Requires 2 moles of ATP for the hexose that is cleaved.
    • ATP Formation from 1,3-Biphosphoglycerate
      • Very specific for glucose; glucose sensor present in pancreatic β cells.
      • Determines the threshold for insulin secretion, influenced by insulin and carbohydrate intake.
      • The first glycolytic step generating ATP, catalyzed by phosphoglycerate kinase.
    • Phosphate Group Shift from Carbon 3 to Carbon 2
      • Catalyzed by phosphoglycerate mutase.
    • 2-Phosphoglycerate Dehydration
      • Catalyzed by enolase.
    • Pyruvate Formation
      • Third irreversible reaction of glycolysis, catalyzed by pyruvate kinase.

    Regulation of Glycolysis

    • Phosphofructokinase 1 (PFK-1) is a key regulatory enzyme, being rate-limiting and controlled by ATP, fructose 6-phosphate, and other effectors.
    • Fructose 1,6-bisphosphate is cleaved by aldolase A in an unregulated reversible reaction.

    Alternate Fates of Pyruvate

    • Oxidative Decarboxylation to Acetyl CoA
      • Important for high oxidative capacity tissues like cardiac muscle.
      • Catalyzed by pyruvate dehydrogenase complex, provides fuel for the TCA cycle and fatty acid synthesis.
    • Carboxylation to Oxaloacetate (OAA)
      • Catalyzed by biotin-dependent pyruvate carboxylase, replenishing TCA cycle intermediates.
    • Reduction to Ethanol (in Yeast and Certain Microorganisms)
      • Involves decarboxylation and alcohol dehydrogenase reactions.
    • Conversion to Alanine
      • Links carbohydrate metabolism with amino acid metabolism, catalyzed by alanine aminotransferase.
    • Reduction to Lactate
      • Final product of anaerobic glycolysis.

    Energy Yield of Glycolysis

    • Anaerobic Glycolysis is significantly faster than aerobic glycolysis, providing ATP without oxygen.
    • Overall reaction for anaerobic glycolysis produces 2 moles of lactate and ATP.
    • Aerobic glycolysis results in 2 moles of pyruvate, ATP, and NADH.

    Inherited Enzyme Deficiencies in Glycolysis

    • Pyruvate Kinase Deficiency is the second most common cause of enzyme deficiency-related hemolytic anemia, primarily affecting erythrocytes.
    • Other deficiencies include Glucose Phosphate Isomerase and Triose Phosphate Isomerase deficiencies.

    Lactic Acidosis

    • Blood lactate levels normally around 1.2 mM; lactic acidosis occurs at levels of 5 mM or more.
    • Results from increased lactate formation or reduced utilization, leading to decreased blood pH and bicarbonate levels.

    Hormonal Regulation of Glycolysis

    • Short-term regulation involves allosteric mechanisms and phosphorylation status of key enzymes, impacting their activity quickly.
    • Hormonal influences, by contrast, have slower but more significant effects, leading to substantial increases in enzyme activity over days.

    Glycolysis and RBC Metabolism

    • Mature red blood cells lack mitochondria and rely entirely on glycolysis for ATP production.

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    Description

    This quiz covers the process of glucose phosphorylation, including the requirement of oxygen to reoxidize NADH, and the mechanisms that effectively trap glucose as glucose 6-phosphate. Explore the irreversible steps involved in this essential biochemical reaction.

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