Glycolysis Overview and Steps

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Questions and Answers

Which of the following enzymes is activated by Fructose-1,6-bisphosphate?

  • Hexokinase
  • Phosphofructokinase-1
  • Glucokinase
  • Pyruvate Kinase (correct)

Which substance inhibits Phosphofructokinase-1 (PFK-1) under high energy conditions?

  • Alanine
  • AMP
  • Fructose-2,6-bisphosphate
  • Citrate (correct)

What is the net gain of ATP from glycolysis per molecule of glucose?

  • 4 ATP
  • 2 ATP (correct)
  • 0 ATP
  • 6 ATP

Which hormone decreases glycolysis in the liver and promotes the activation of AMP kinase?

<p>Glucagon (A)</p>
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Hexokinase is inhibited by which of the following?

<p>Glucose-6-phosphate (D)</p>
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What is the primary product of glycolysis under aerobic conditions?

<p>Pyruvate (B)</p>
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Where does glycolysis occur within the cell?

<p>Cytoplasm (C)</p>
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Which enzyme catalyzes the irreversible step of converting Glucose to Glucose-6-Phosphate?

<p>Hexokinase (A)</p>
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Which of the following intermediates is produced when Dihydroxyacetone Phosphate is converted to Glyceraldehyde-3-Phosphate?

<p>Glyceraldehyde-3-Phosphate (C)</p>
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What inhibits Phosphofructokinase-1 during glycolysis?

<p>ATP (C)</p>
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Which step of glycolysis generates NADH?

<p>Glyceraldehyde-3-Phosphate to 1,3-Bisphosphoglycerate (D)</p>
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What is the role of Pyruvate Kinase in glycolysis?

<p>To convert Phosphoenolpyruvate to Pyruvate (A)</p>
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Which tissue is especially reliant on glycolysis for quick energy during exercise?

<p>Muscle (D)</p>
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Flashcards

Phosphofructokinase-1 (PFK-1)

The enzyme responsible for converting fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis. It is a key regulatory step in the process.

AMP (Adenosine Monophosphate)

A molecule that activates PFK-1, indicating a low-energy state. It promotes glycolysis to generate more ATP.

ATP (Adenosine Triphosphate)

A compound that inhibits PFK-1, indicating a high-energy state. It slows down glycolysis when ATP levels are sufficient.

Allosteric Regulation

A process that occurs when an enzyme's activity is regulated by the binding of a molecule other than its substrate.

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Irreversible Step

The conversion of a molecule from one form to another, often involving a chemical reaction. In glycolysis, irreversible steps cannot be reversed by simply reversing the reaction.

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What is Glycolysis?

The metabolic pathway that converts glucose into pyruvate (or lactate in anaerobic conditions), generating ATP and NADH. It occurs in the cytoplasm of the cell and is anaerobic (does not require oxygen).

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Where does Glycolysis occur?

Glycolysis primarily takes place in the cytoplasm of the cell, not within the mitochondria.

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Explain the first step of glycolysis.

The phosphorylation of glucose to glucose-6-phosphate (G6P) using the enzyme hexokinase traps glucose inside the cell, and is an irreversible step.

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What is the rate-limiting step of glycolysis?

The conversion of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (F1,6BP) using the enzyme phosphofructokinase-1 (PFK-1) is the rate-limiting step of glycolysis. It involves the consumption of ATP and is irreversible.

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How is glycolysis regulated?

Glycolysis can be regulated at various steps, but most notably through the activity of PFK-1. It is activated by AMP and Fructose-2,6-Bisphosphate (F2,6BP) and inhibited by ATP, Citrate, and H+ (low pH).

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What happens in the oxidation step of glycolysis?

Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate (1,3-BPG) and generates NADH by reducing NAD+. This step is reversible.

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How is ATP produced during glycolysis?

In the conversion of 1,3-bisphosphoglycerate (1,3-BPG) to 3-phosphoglycerate (3PG) using phosphoglycerate kinase, ATP is produced via substrate-level phosphorylation. This process involves the transfer of a phosphate group from a substrate to ADP.

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What is the final step of glycolysis?

The final step of glycolysis involves the conversion of phosphoenolpyruvate (PEP) to pyruvate using the enzyme pyruvate kinase. This reaction generates one molecule of ATP per pyruvate molecule, making it an important step for energy production.

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Study Notes

Glycolysis Overview

  • Glycolysis is a metabolic pathway that converts glucose into pyruvate (or lactate anaerobically).
  • It produces ATP and NADH.
  • It occurs in the cytoplasm of cells.
  • It's an anaerobic process (doesn't require oxygen).
  • Crucial for rapid energy production, especially in muscle during exercise.
  • Essential for various tissues, particularly muscle, red blood cells, and brain.
  • The liver carries out glycolysis, especially during fasting (to produce and transport glucose).

Location and Intermediates

  • Occurs in the cytoplasm.
  • Some glycolysis intermediates (like pyruvate) are transported to the mitochondria for further metabolism.

Glycolysis Steps

  • Glucose → Glucose-6-Phosphate (G6P):

    • Enzyme: Hexokinase (or Glucokinase in liver).
    • Irreversible step; traps glucose inside the cell.
    • Regulated by: G6P (product inhibition), insulin (induces glucokinase), fructose-6-phosphate (inhibits glucokinase), and glucose-6-phosphate (inhibits hexokinase).

  • Glucose-6-Phosphate → Fructose-6-Phosphate (F6P):

    • Enzyme: Phosphoglucose Isomerase
    • Reversible step

  • Fructose-6-Phosphate → Fructose-1,6-Bisphosphate (F1,6BP):

    • Enzyme: Phosphofructokinase-1 (PFK-1).
    • Irreversible step; rate-limiting step of glycolysis. Consumes ATP.
    • Regulated by: AMP, F2,6BP (activates), ATP, citrate, and H+ (inhibits).

  • Fructose-1,6-Bisphosphate → Glyceraldehyde-3-Phosphate (G3P) and Dihydroxyacetone Phosphate (DHAP):

    • Enzyme: Aldolase.
    • Reversible step

  • Dihydroxyacetone Phosphate → Glyceraldehyde-3-Phosphate (G3P):

    • Enzyme: Triose Phosphate Isomerase
    • Reversible step.

  • Glyceraldehyde-3-Phosphate → 1,3-Bisphosphoglycerate (1,3-BPG):

    • Enzyme: Glyceraldehyde-3-Phosphate Dehydrogenase.
    • Generates NADH by reducing NAD+.
    • Reversible step

  • 1,3-Bisphosphoglycerate → 3-Phosphoglycerate (3PG):

    • Enzyme: Phosphoglycerate Kinase.
    • Produces ATP (substrate-level phosphorylation).
    • Reversible step.

  • 3-Phosphoglycerate → 2-Phosphoglycerate (2PG):

    • Enzyme: Phosphoglycerate Mutase
    • Reversible step.

  • 2-Phosphoglycerate → Phosphoenolpyruvate (PEP):

    • Enzyme: Enolase.
    • Reversible step.

  • Phosphoenolpyruvate → Pyruvate:

    • Enzyme: Pyruvate Kinase.
    • Irreversible step. Produces ATP.
    • Regulated by: F1,6BP (activates), ATP, and Alanine (inhibits).

Irreversible Steps

  • Glucose → G6P (hexokinase/glucokinase)
  • F6P → F1,6BP (PFK-1)
  • PEP → Pyruvate (pyruvate kinase)

Regulation of Glycolysis

  • Hormonal Regulation:

    • Insulin: Activates glycolysis.
    • Glucagon: Inhibits glycolysis.

  • Allosteric Regulation:

    • PFK-1 is activated by AMP and F2,6BP, inhibited by ATP and citrate.
    • Pyruvate kinase is activated by F1,6BP, inhibited by ATP and alanine.
    • Hexokinase is inhibited by its product, G6P.
    • Glucokinase (liver) is not inhibited by G6P, regulated by glucose availability.

  • Energetic Feedback:

    • ATP and NADH accumulation inhibits further glycolysis.
    • AMP and ADP stimulate glycolysis during low energy.

Energetic Summary

  • Glycolysis produces 2 net ATP and 2 NADH per glucose molecule.
  • NADH can be used in oxidative phosphorylation if oxygen is available.

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