Biochemistry Chapter 11: Glycolysis
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Questions and Answers

What molecule is generated when hexokinase phosphorylates glucose?

  • Glucose
  • Glucose 6-phosphate (correct)
  • ATP
  • Fructose 6-phosphate

    • Which of the following is true regarding hexokinases?

  • Hexokinases cannot phosphorylate fructose.
  • Hexokinase IV is the most active at low glucose concentrations.
  • Hexokinase I, II, III are active at normal glucose levels. (correct)
  • Hexokinases require calcium ions for their activity.

    • What distinguishes glucokinase from other hexokinases?

  • It functions in the brain.
  • It responds to high glucose levels in the liver. (correct)
  • It can become saturated with glucose at normal levels.
  • It has a lower Km value than other hexokinases.

    • What is the role of Mg2+ in the activity of kinases in glycolysis?

    <p>It acts as a co-factor for all kinases.</p> Signup and view all the answers

    What type of reaction does phosphoglucose isomerase catalyze?

    <p>Isomerization of G6P to F6P</p> Signup and view all the answers

    In which step of glycolysis is glucose phosphorylated by phosphofructokinase-1 (PFK-1)?

    <p>Step 3</p> Signup and view all the answers

    How does glucose 6-phosphate prevent glucose from leaving the cell?

    <p>By changing its charge after phosphorylation.</p> Signup and view all the answers

    Why is the isomerization reaction catalyzed by phosphoglucose isomerase considered near-equilibrium?

    <p>The concentrations of substrates and products are balanced.</p> Signup and view all the answers

    What is the net production of ATP per glucose molecule during glycolysis?

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

    What is the main product of the reaction catalyzed in Steps 6 and 7 of glycolysis?

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

    What are the end products of glycolysis?

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

    Which enzyme catalyzes the transfer of a phosphoryl group in Step 8?

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

    What is the significance of phosphoenolpyruvate (PEP) in Step 9 of glycolysis?

    <p>It is a substrate for pyruvate kinase.</p> Signup and view all the answers

    Which stage of glycolysis consumes ATP?

    <p>Hexose stage</p> Signup and view all the answers

    Which aspect of the reaction catalyzed by Pyruvate Kinase is true?

    <p>It is metabolically irreversible.</p> Signup and view all the answers

    How many enzyme-catalyzed reactions are involved in glycolysis?

    <p>10 reactions</p> Signup and view all the answers

    In which part of the cell does glycolysis primarily occur?

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

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

    <p>It transfers a phosphoryl group from ATP to fructose-6-phosphate.</p> Signup and view all the answers

    Which of the following statements about glycolysis is true?

    <p>It can occur in the absence of oxygen.</p> Signup and view all the answers

    What is primarily released during the conversion of glucose to pyruvate in glycolysis?

    <p>Chemical energy</p> Signup and view all the answers

    Which enzyme-catalyzed reaction is irreversible in glycolysis?

    <p>Phosphofructokinase reaction</p> Signup and view all the answers

    What role do magnesium ions play in the hydration reaction led by Enolase in Step 9?

    <p>They help in the dehydration process.</p> Signup and view all the answers

    Which statement correctly describes Aldolase's role in glycolysis?

    <p>Aldolase cleaves fructose-1,6-bisphosphate into two triose phosphates.</p> Signup and view all the answers

    Why is the PFK-1 reaction considered metabolically irreversible?

    <p>It is a control point for the glycolysis pathway.</p> Signup and view all the answers

    What are the products formed when Aldolase cleaves fructose-1,6-bisphosphate?

    <p>Glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.</p> Signup and view all the answers

    What distinguishes class I aldolases from class II aldolases?

    <p>Class I aldolases are common in plants and animals, while class II is more common in bacteria and fungi.</p> Signup and view all the answers

    What is the significance of the aldolase reaction in glycolysis?

    <p>It represents a near-equilibrium biosynthesis reaction.</p> Signup and view all the answers

    How did the pathways related to fructose-1,6-bisphosphate emergence evolve?

    <p>The synthesis pathway was developed first, leading to its degradation.</p> Signup and view all the answers

    What is the role of fructose-2,6-bisphosphate in relation to PFK-1?

    <p>It enhances the activity of PFK-1.</p> Signup and view all the answers

    Which molecule is a substrate for the next reaction in the glycolytic pathway after the splitting of fructose 1,6-bisphosphate?

    <p>Glyceraldehyde 3-phosphate (G3P)</p> Signup and view all the answers

    What type of isomer is produced from Dihydroxyacetone phosphate (DHAP) in the isomerization reaction?

    <p>D-isomer</p> Signup and view all the answers

    What product is formed from the oxidation of glyceraldehyde 3-phosphate by GAPDH?

    <p>1,3-bisphosphoglycerate</p> Signup and view all the answers

    During the conversion of glyceraldehyde 3-phosphate, what happens to NAD+?

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

    What is conserved in the form of reducing equivalents during the phosphorylation by Phosphoglycerate Kinase?

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

    What product is generated when the C-1 phosphoryl group of 1,3-bisphosphoglycerate is transferred to ADP?

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

    In which step of glycolysis does the reduction of NAD+ to NADH occur?

    <p>Oxidation with GAPDH</p> Signup and view all the answers

    What distinguishes the energy change during the oxidation of glyceraldehyde 3-phosphate?

    <p>It proceeds with a large negative free-energy change.</p> Signup and view all the answers

    Study Notes

    Glycolysis Overview

    • Glycolysis is the metabolic pathway that converts glucose into pyruvate through a sequence of ten enzyme-catalyzed reactions.
    • It occurs in the cytosol and is a primary energy source in animals.
    • Glycolysis can be divided into two stages: hexose stage (consumes 2 ATP) and triose stage (produces 4 ATP), yielding a net gain of 2 ATP per glucose molecule.

    Steps of Glycolysis

    • Step 1: Hexokinase Reaction

      • Transfers a phosphate group from ATP to glucose, forming glucose 6-phosphate (G6P).
      • Requires Mg2+ and is catalyzed by hexokinase, showing broad substrate specificity.

    • Step 2: Isomerization

      • G6P is converted to fructose 6-phosphate (F6P) by phosphoglucose isomerase (PGI).
      • Reaction operates near equilibrium.

    • Step 3: Phosphorylation by PFK-1

      • F6P is phosphorylated to fructose 1,6-bisphosphate (F1,6BP) using ATP.
      • PFK-1 is a critical regulatory step and commits glucose to glycolysis.

    • Step 4: Cleavage

      • Aldolase splits F1,6BP into two triose phosphates: glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP).
      • This reaction is not a control point and is near equilibrium.

    • Step 5: Isomerization by TPI

      • DHAP is converted into G3P through triose phosphate isomerase (TPI).
      • Only G3P proceeds in the glycolytic pathway.

    Energy Yield

    • Glycolysis yields a net of 2 ATP molecules and 2 NADH per glucose.
    • ATP is produced through substrate-level phosphorylation in steps 7 and 10.

    Steps Involving ATP Generation

    • Step 6: Oxidation by GAPDH

      • G3P is oxidized to 1,3-bisphosphoglycerate (1,3BPG) with the reduction of NAD+ to NADH.

    • Step 7: Phosphorylation by PGK

      • 1,3BPG donates a phosphate to ADP, generating ATP and forming 3-phosphoglycerate (3PG).

    Additional Steps

    • Step 8: Phosphoryl Group Shift

      • Phosphoglycerate mutase transfers a phosphate group within 3PG to form 2-phosphoglycerate (2PG), with no ATP required.

    • Step 9: Dehydration by Enolase

      • 2PG is dehydrated to phosphoenolpyruvate (PEP), a high-energy compound.

    • Step 10: Final ATP Generation by PK

      • PEP transfers a phosphate to ADP, forming ATP and resulting in pyruvate.
      • This step is irreversible and regulated by various hormones and nutrient levels.

    Key Regulatory Points

    • PFK-1 is a major regulatory enzyme of glycolysis, and its regulation is crucial for metabolic control.
    • Hexokinase and pyruvate kinase also play important roles in regulating glycolysis, responding to substrate availability.

    Importance of Glycolysis

    • Glycolysis is essential in carbohydrate metabolism and energy production, forming the basis for further metabolic pathways, including gluconeogenesis and the citric acid cycle.
    • It ensures energy production even in cells with limited oxygen availability (e.g., in the retina and certain brain cells).

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    Description

    This quiz covers the fundamental concepts of glycolysis, including its definition and the 10-step process. You'll identify the irreversible reactions along with their substrates, products, and enzymes, as well as calculate energy yield. Additionally, the quiz will differentiate between carbohydrates and their various types.

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