Glycolysis Overview and Phases

Glycolysis Overview

• Definition: Glycolysis is a metabolic pathway that converts glucose into pyruvate, generating energy in the form of ATP and NADH.
• Location: Occurs in the cytoplasm of cells.

Phases of Glycolysis

1. Energy Investment Phase:

   • Consumes energy (2 ATP).
   • Converts glucose to fructose-1,6-bisphosphate.
   • Key enzymes:
     • Hexokinase (glucose to glucose-6-phosphate)
     • Phosphofructokinase-1 (fructose-6-phosphate to fructose-1,6-bisphosphate).

2. Energy Payoff Phase:

   • Produces energy (4 ATP, 2 NADH).
   • Converts glyceraldehyde-3-phosphate to pyruvate.
   • Key enzymes:
     • Glyceraldehyde-3-phosphate dehydrogenase (produces NADH)
     • Pyruvate kinase (produces ATP and pyruvate).

Key Products

• Net Gain:
  • 2 ATP (4 produced - 2 used)
  • 2 NADH
  • 2 Pyruvate molecules.

Regulation

• Key Regulatory Enzymes:
  • Hexokinase: inhibited by glucose-6-phosphate.
  • Phosphofructokinase-1: regulated by ATP (inhibition) and AMP (activation).
  • Pyruvate kinase: activated by fructose-1,6-bisphosphate.

Importance

• Central pathway in cellular respiration.
• Provides substrates for further energy production in aerobic and anaerobic conditions.
• Plays a crucial role in metabolism and energy balance.

Anaerobic Fate of Pyruvate

• In absence of oxygen:
  • Conversion to lactate (in animals) or ethanol and CO2 (in yeast).

Summary

• Glycolysis is a fundamental biochemical pathway for energy production, involving a series of enzymatic reactions that convert glucose into pyruvate while generating ATP and NADH.

Glycolysis Overview

• Glycolysis is a metabolic pathway transforming glucose into pyruvate while generating ATP and NADH.
• The entire process takes place in the cytoplasm of cells.

Phases of Glycolysis

• Energy Investment Phase:

  • Consumes 2 ATP molecules to initiate glucose conversion.
  • Converts glucose to fructose-1,6-bisphosphate.
  • Key enzymes include:
    • Hexokinase: converts glucose to glucose-6-phosphate.
    • Phosphofructokinase-1: converts fructose-6-phosphate to fructose-1,6-bisphosphate.

• Energy Payoff Phase:

  • Produces 4 ATP and 2 NADH by converting glyceraldehyde-3-phosphate to pyruvate.
  • Key enzymes include:
    • Glyceraldehyde-3-phosphate dehydrogenase: produces NADH.
    • Pyruvate kinase: generates ATP and converts phosphoenolpyruvate to pyruvate.

Key Products

• Net Gain:
  • 2 ATP (4 produced minus 2 used).
  • 2 NADH molecules.
  • 2 pyruvate molecules are produced.

Regulation

• Key Regulatory Enzymes:
  • Hexokinase: inhibited by glucose-6-phosphate to prevent excess glucose utilization.
  • Phosphofructokinase-1: inhibited by ATP (indicating high energy) and activated by AMP (indicating low energy).
  • Pyruvate kinase: activated by fructose-1,6-bisphosphate to enhance glycolytic flux.

Importance

• Glycolysis serves as a central pathway in cellular respiration.
• It provides essential substrates for energy production under both aerobic and anaerobic conditions.
• Plays a vital role in overall metabolism and maintaining energy balance in cells.

Anaerobic Fate of Pyruvate

• In the absence of oxygen, pyruvate can be converted to:
  • Lactate in animal cells.
  • Ethanol and carbon dioxide in yeast.