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.