Biochemistry: Glucose Metabolism Lecture
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Questions and Answers

What type of phosphorylation occurs during the conversion of 1,3-Bisphosphoglycerate to 3-Phosphoglycerate?

  • Oxidative phosphorylation
  • Substrate level phosphorylation (correct)
  • Oxidative decarboxylation
  • Photophosphorylation

    • How many molecules of ATP are produced in the reaction catalyzed by ATP kinase when converting Phosphoenolpyruvate to Pyruvate?

  • Three molecules
  • Two molecules (correct)
  • Four molecules
  • One molecule

    • Which molecule is formed as a product of the reaction catalyzed by enolase?

  • 1,3-Bisphosphoglycerate
  • 2-Phosphoglycerate
  • Pyruvate
  • Phosphoenolpyruvate (correct)

    • What is the main role of the enzyme mutase in glycolysis?

    <p>Move phosphate groups</p> Signup and view all the answers

    Why is the reaction converting 3-Phosphoglycerate to 2-Phosphoglycerate considered unremarkable?

    <p>It merely involves the movement of a phosphate group</p> Signup and view all the answers

    In the glycolytic pathway, at which stage is NADH produced?

    <p>During the conversion of Glyceraldehyde-3-phosphate</p> Signup and view all the answers

    Which compound serves as a key intermediate before ATP synthesis occurs from 1,3-Bisphosphoglycerate?

    <p>3-Phosphoglycerate</p> Signup and view all the answers

    What is primarily happening when the enzyme ATP kinase functions in glycolysis?

    <p>Transfer of phosphate from a substrate to ADP</p> Signup and view all the answers

    What is the net yield of ATP from glycolysis after considering the early and later stages?

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

    Which cofactor is regenerated during the conversion of pyruvate to lactate?

    <p>NAD+</p> Signup and view all the answers

    How does the body respond to limited oxygen supplies regarding pyruvate metabolism?

    <p>Pyruvate is converted to lactate</p> Signup and view all the answers

    Which of the following is NOT a metabolic fate of pyruvate when oxygen is present?

    <p>Conversion to lactate</p> Signup and view all the answers

    What type of control primarily regulates the pathway of glycolysis?

    <p>Allosteric and hormonal control</p> Signup and view all the answers

    Which molecule serves as the allosteric inhibitor for phosphofructokinase?

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

    In the case of excess caloric intake, pyruvate is primarily converted into which of the following?

    <p>Fatty acids</p> Signup and view all the answers

    What is the primary role of lactate dehydrogenase in the context of pyruvate metabolism?

    <p>Catalyzes the conversion of pyruvate to lactate</p> Signup and view all the answers

    What is the primary energy yield from glycolysis?

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

    Which cell type relies solely on glycolysis for ATP production due to lack of mitochondria?

    <p>Red blood cells</p> Signup and view all the answers

    What is produced at a high rate by tumour cells through anaerobic glycolysis?

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

    Which pathway allows for ATP production under both aerobic and anaerobic conditions?

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

    Which of the following substances is a main intermediate produced during glycolysis and can enter the mitochondria for further ATP production?

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

    Which tissues are specifically noted for their high reliance on glycolysis?

    <p>Brain, skeletal muscle, and red blood cells</p> Signup and view all the answers

    What effect does ATP have on phosphofructokinase during glycolysis?

    <p>It inhibits the enzyme</p> Signup and view all the answers

    What is the Warburg effect commonly associated with in terms of cellular metabolism?

    <p>Preferential anaerobic glycolysis in tumor cells</p> Signup and view all the answers

    What is the primary function of the liver in relation to glucose compared to the brain when blood glucose levels are low?

    <p>Store excess glucose efficiently</p> Signup and view all the answers

    In which reaction does fructose 6-phosphate convert to fructose 1,6-bisphosphate?

    <p>Phosphofructo-kinase</p> Signup and view all the answers

    What is the result of the reaction involving aldolase?

    <p>Conversion of a 6-carbon sugar into two 3-carbon units</p> Signup and view all the answers

    What is the significance of the reaction involving glyceraldehyde 3-phosphate dehydrogenase?

    <p>It generates NADH, which is used later in oxidative phosphorylation</p> Signup and view all the answers

    Which substance is produced when glyceraldehyde 3-phosphate undergoes oxidation?

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

    What explains the higher Km and higher Vmax of the liver's glucose utilization compared to that of muscles?

    <p>The liver must store excess glucose when levels are high</p> Signup and view all the answers

    How many times will all reactions occur from glucose to produce ATP through glycolysis?

    <p>Twice, because two 3-carbon units are produced</p> Signup and view all the answers

    Which reaction serves as a key regulatory step in glycolysis?

    <p>Conversion of fructose 6-phosphate to fructose 1,6-bisphosphate</p> Signup and view all the answers

    What is the correct net yield of ATP from anaerobic glycolysis?

    <p>2 ATP per glucose molecule</p> Signup and view all the answers

    During anaerobic glycolysis, how many ATP molecules are consumed in the initial steps?

    <p>2 ATP are consumed</p> Signup and view all the answers

    In anaerobic glycolysis, which compound is primarily produced from glucose?

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

    What role does NAD+ play during anaerobic glycolysis?

    <p>It is reduced to NADH</p> Signup and view all the answers

    In anaerobic conditions, what happens to the pyruvate produced during glycolysis?

    <p>It is fermented to lactate</p> Signup and view all the answers

    Which enzyme is responsible for converting glucose to glucose 6-phosphate in glycolysis?

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

    What is the terminal product of anaerobic glycolysis?

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

    How many total ATP molecules can be generated from one molecule of glucose during glycolysis, considering both invested and produced ATP?

    <p>4 ATP molecules</p> Signup and view all the answers

    Which intermediate is formed after the conversion of fructose 1,6-bisphosphate in glycolysis?

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

    What is the primary function of glycolysis in cellular metabolism?

    <p>ATP synthesis and energy capture</p> Signup and view all the answers

    Which of the following enzymes is responsible for the phosphorylation of glucose in the glycolysis pathway?

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

    What type of molecule is glucose classified as?

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

    What are the end products of glycolysis from one molecule of glucose?

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

    Which of the following is NOT a source of glucose for glycolysis?

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

    What is the role of lactate dehydrogenase in anaerobic conditions?

    <p>To regenerate NAD+ from NADH</p> Signup and view all the answers

    Which of the following statements about ATP synthesis in glycolysis is true?

    <p>ATP is produced by substrate-level phosphorylation</p> Signup and view all the answers

    In which part of the cell does glycolysis take place?

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

    Which enzyme in glycolysis is specifically inhibited by glucose-6-phosphate?

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

    Which metabolic event occurs during the oxidation phase of glycolysis?

    <p>Removal of hydrogen atoms</p> Signup and view all the answers

    What is the significance of the high Km of glucokinase?

    <p>It allows the liver to respond to high glucose levels</p> Signup and view all the answers

    Which statement correctly describes the role of glycolysis in red blood cells?

    <p>Glycolysis is the only source of ATP</p> Signup and view all the answers

    Why is it important to regenerate NAD+ in the glycolysis pathway?

    <p>It allows glycolysis to continue running</p> Signup and view all the answers

    Study Notes

    Lecture: Glucose metabolism: glycolysis and Anaerobic metabolism

    • The lecture was delivered by Dr. Lauren Albee, from the Department of Biochemistry, King's College London.
    • The lecture focused on glucose metabolism, specifically glycolysis and anaerobic metabolism.
    • Relevant textbook chapters include Chapters 11 (pages 181-187) and 13 (pages 210-215) of Biochemistry and Molecular Biology.
    • The lecture materials are available as an e-textbook at https://bibliu.com/app/#/signinPage.

    Learning Outcomes

    • Students should be able to draw structures of glucose and glycogen.
    • Students should be able to outline metabolic events involved in converting glucose to pyruvate through glycolysis.
    • Students should be able to explain ATP formation from ADP through substrate-level phosphorylation.
    • Students should be able to describe NAD+ regeneration from NADH under aerobic and anaerobic conditions, highlighting the role of lactate dehydrogenase in muscle.
    • Students should be able to illustrate a control mechanism in glycolysis regulation.
    • Students should be able to summarize glycolysis's roles in various tissues, such as red blood cells.

    Structure and Function of Glucose and Glycogen

    • Glucose: A monosaccharide, approximately 10 g present in plasma. It's osmotically active and a primary immediate energy source, utilized in glycolysis. It's also a precursor for gluconeogenesis.
    • Glycogen: A polysaccharide stored in tissues (approximately 400 g), characterized by low osmolarity and a medium-term energy storage function.

    Glycolysis: Key Points

    • Definition: The conversion of glucose (C₆H₁₂O₆) to two molecules of pyruvate (C₃H₄O₃).
    • Location: Cytosol (10 soluble enzymes).
    • Tissues: All tissues.
    • Functions: Energy trapping (ATP synthesis), precursor for fat synthesis, and precursor for amino acid synthesis.

    Sources of Glucose for Glycolysis

    • Dietary sugars and starches.
    • Breakdown of stored glycogen in the liver.
    • Recycled glucose from lactic acid, amino acids, or glycerol.

    Glycolysis: Summary Diagram (and reactions)

    • This section details the chemical steps involved in glycolysis, showing the sequential conversion of glucose to pyruvate along with various enzymes involved - (chemical structures).

    The 10 Reactions of Glycolysis

    • The 10 reactions of glycolysis can be categorized into 4 stages:
      • Activation (using ATP)
      • Splitting the 6-carbon sugar into two 3-carbon units.
      • Oxidation (removing 2 hydrogen atoms).
      • Synthesis of ATP.

    Reaction 1 (Trapping Glucose)

    • Hexokinase or glucokinase adds a phosphate group to glucose, trapping it inside the cell.
    • Hexokinase is active in all tissues except the liver, and Glucokinase is active in the liver.

    Reaction 2 (Isomerization)

    • A simple isomerization step. Glucose-6-phosphate is converted into fructose-6-phosphate for subsequent reactions via phosphohexose isomerase.

    Reaction 3 (Key Regulatory Step - Phosphorylation)

    • Phosphofructokinase is a key regulatory step in glycolysis, and it uses ATP to create fructose 1,6-bisphosphate.

    Splitting of the 6-carbon Sugar to 3-Carbon Units

    • Aldolase catalyzes the splitting of fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

    Oxidation Step (Reaction 6)

    • Key step where NAD+ is reduced to NADH, along with the production of 1,3-bisphosphoglycerate.

    ATP Synthesis Stages (reactions 7-10)

    • A series of reactions where ATP is produced from ADP via substrate-level phosphorylation, focusing on the importance of 1,3-bisphosphoglycerate, 3-phosphoglycerate kinase, and pyruvate kinase.

    Reaction 7 (Substrate-Level Phosphorylation)

    • The 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate with a simultaneous production of ATP via 3-phosphoglycerate kinase.
    • This reaction occurs twice for each glucose molecule.

    Reaction 8 (Isomerization)

    • A simple isomerization step catalyzed by phosphoglycerate mutase, converting 3-phosphoglycerate to 2-phosphoglycerate. This converts the position of the phosphate group

    Reaction 9 (Dehydration)

    • Dehydration reaction by enolase, converting 2-phosphoglycerate to phosphoenolpyruvate.

    Reaction 10 (Substrate-Level Phosphorylation)

    • Pyruvate kinase catalyzes the final step, converting phosphoenolpyruvate to pyruvate, producing ATP.
    • This is an irreversible step. This step occurs twice per glucose molecule.

    Summary Slide: Yields of ATP from Glycolysis

    • Early stages consume 2 ATP.
    • Later stages produce 4 ATP.
    • Net yield: 2 ATP (plus further ATP from mitochondrial metabolism from 2 NADH).

    Anaerobic Glycolysis

    • Low oxygen supply results in converting pyruvate to lactate to achieve NAD+ regeneration.
    • The reaction is catalyzed by lactate dehydrogenase.

    Reaction Catalyzed by Lactate Dehydrogenase

    • The reaction is reversible and utilizes NADH, converting pyruvate to lactate.
    • This pathway is critical when oxygen availability is limited.

    Metabolic Fates of Pyruvate

    • The metabolic fate of pyruvate depends on the presence or absence of oxygen:
      • Anaerobic conditions: Pyruvate is reduced to lactate.
      • Aerobic conditions: Pyruvate enters the mitochondria to be used in the citric acid cycle. Other pathways include fatty acid synthesis.

    Regulation of Glycolysis

    • Primarily under allosteric control (e.g., phosphofructokinase).
    • Hormonal control is also involved, but not discussed in detail in this lecture.

    Allosteric Control of Phosphofructokinase

    • The enzyme phosphofructokinase is a key regulator of glycolysis, influenced by allosteric effectors like ATP, ADP, and citrate.
    • Think of cellular energy needs determining whether glycolysis should occur or be inhibited.

    Allosteric Inhibition of Phosphofructokinase by ATP

    • High ATP concentrations inhibit phosphofructokinase, slowing the glycolysis reaction rate. This is through its binding to an allosteric site.

    Specialized Functions in Tissues

    • Skeletal muscle: Rapid ATP production during intense exercise.
    • Red blood cells: Sole pathway for ATP generation (lacking mitochondria).
    • Brain: Major ATP source (cannot use fats as primary energy).

    Summary of Glycolysis

    • Principal catabolic pathway for glucose utilization (occurs in all tissues).
    • Unique capacity for functioning in both aerobic and anaerobic conditions (red blood cells and muscle cells).
    • Low ATP yield but critical for fast energy, and an input for subsequent reactions in the cell.
    • Intermediate products can be used for fatty acid synthesis and other metabolic processes.

    Discoveries and Dilemmas

    • "Extras" and topics for further thought and investigation, not part of the required learning for this lecture..

    The Warburg Effect

    • Tumour cells exhibit high rates of glycolysis even when mitochondria are present. They produce far more lactate than healthy cells.
    • This effect allows for rapid ATP synthesis and the generation of intermediates for biosynthetic reactions required for rapid cellular growth.

    Multiple Choice Questions (MCQs)

    • The document includes MCQ questions covering end products of glycolysis, tissues where glycolysis is essential, anaerobic glycolysis ATP yield, crucial glycolytic reactions, and enzymes involved in substrate-level phosphorylation. Answers are NOT included here.

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    Description

    This quiz covers glucose metabolism with a focus on glycolysis and anaerobic metabolism based on Dr. Lauren Albee's lecture from King's College London. Students will explore key biochemical processes, including ATP formation and NAD+ regeneration. Relevant textbook chapters are included for reference.

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