Glycolysis Overview and Phases

May 2, 2025

Overview of Glycolysis

Introduction

  • Glycolysis is the first phase of cellular respiration.
  • It involves the breakdown of glucose into two 3-carbon compounds.
  • Two ATP molecules are used during the investment phase and a net of two ATPs are generated in the payoff phase.

Phases of Glycolysis

Investment Phase

  • Uses 2 ATPs to start the process.
  • Glucose (C6H12O6) is broken down into two 3-carbon compounds, each with a phosphate group.
  • The phosphate groups are derived from ATPs.
  • This phase is analogous to an investment in a business.

Payoff Phase

  • Each of the 3-carbon compounds (PGAL) is converted into pyruvate.
  • During this conversion, 2 ATPs and 1 NADH are produced for each PGAL.
  • Total for one glucose: 4 ATPs and 2 NADHs.
  • The payoff phase results in a net gain of 2 ATPs because 2 ATPs are used in the investment phase.

Key Terms and Definitions

  • Pyruvate: The end product of glycolysis, a 3-carbon compound.
  • NADH: Produced by the reduction of NAD+, where it gains a hydrogen.
  • ATP: Adenosine Triphosphate, the energy currency of the cell.
  • PGAL (Phosphoglyceraldehyde): Intermediate in glycolysis.

Chemical Reaction

  • Inputs: Glucose, 2 NAD+, 2 ATP, 4 ADP, 4 Phosphate groups.
  • Outputs: 2 Pyruvates, 2 NADH, 4 ATP (gross), 2 ATP (net).

Biological Context

  • Glycolysis can occur with or without oxygen.
  • In anaerobic conditions, fermentation occurs, leading to lactic acid or ethanol production.
  • In the presence of oxygen, glycolysis is followed by the Krebs Cycle and the Electron Transport Chain for further ATP production.

Additional Information

  • Glycolysis involves an initial use of ATP (investment) but produces a net gain due to subsequent ATP generation.
  • Two molecules of NADH, formed, are later used in the electron transport chain.

Conclusion

  • Glycolysis is a critical metabolic pathway, providing energy and precursors for further cellular processes.
  • Understanding glycolysis lays the foundation for further study of cellular respiration and bioenergetics.