Lecture Notes: Glycolysis

Introduction

• Energy Requirement:
  • Necessary for all activities (running, breathing)
  • Produced by every cell constantly
• Energy Source:
  • Originates from the sun via nuclear fusion
  • Absorbed by plants through photosynthesis to create glucose

Cellular Respiration

• Definition: Degradation of biomolecules to generate energy
• Process: Involves aerobic respiration (requires oxygen)
• Analogy: Compared to engine combustion reactions
• Electron Carriers: NAD+ and NADH involved in electron exchanges, facilitated by dehydrogenase enzymes

Major Pathways of Cellular Respiration

1. Glycolysis: Occurs in the cytoplasm, no oxygen required (anaerobic)
2. Citric Acid Cycle
3. Oxidative Phosphorylation

Glycolysis Overview

• Location: Cytoplasm
• Anaerobic Process: Does not require oxygen, ancient pathway
• Products: Splits glucose into two pyruvate molecules
• Energy Yield: Net gain of 2 ATP per glucose molecule

Glycolysis Steps

Preparatory Phase

1. Hexokinase Reaction:
   • Phosphorylation of glucose to glucose 6-phosphate (costs 1 ATP)
2. Phosphoglucoisomerase Reaction:
   • Isomerization to fructose-6-phosphate
3. Phosphofructokinase-1 Reaction:
   • Phosphorylation to fructose-1,6-bisphosphate (costs 1 ATP)
4. Fructose Bisphosphate Aldolase Reaction:
   • Splits into glyceraldehyde-3-phosphate (GADP) and dihydroxyacetone phosphate (DHAP)
5. Triosephosphate Isomerase Reaction:
   • Converts DHAP to a second GADP

Payoff Phase

1. Glyceraldehyde Phosphate Dehydrogenase Reaction:
   • Oxidation to 1,3-bisphosphoglycerate (requires NAD+ and inorganic phosphate)
2. Phosphoglycerate Kinase Reaction:
   • Produces ATP from ADP; forms 3-phosphoglycerate
3. Phosphoglycerate Mutase Reaction:
   • Transfers phosphate to form 2-phosphoglycerate
4. Enolase Reaction:
   • Dehydration to phosphoenolpyruvate
5. Pyruvate Kinase Reaction:
   • Produces ATP; generates pyruvate

Summary of Glycolysis

• Total Steps: 10 steps
• Phase Breakdown:
  • Preparatory Phase: 5 steps, consumes 2 ATP
  • Payoff Phase: 5 steps, produces 4 ATP
• Net Gain: 2 ATP per glucose
• Key Outcome: Conversion of glucose to pyruvate in the cytoplasm

Additional Resources

• Details of enzymes and inputs/outputs for each step available
• Encourage memorization of basic facts and specific details as needed
• Pyruvate proceeds to the next stage of cellular respiration

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