Cellular Respiration: Glycolysis Focus

May 21, 2024

Cellular Respiration: Glycolysis Focus ⚛️

Overview

  • Cellular respiration is divided into three main stages:
    1. Glycolysis
    2. Krebs Cycle (Citric Acid Cycle)
    3. Electron Transport Chain (ETC)
  • Glycolysis: Breakdown of glucose
  • Glycolysis occurs with or without oxygen
  • In anaerobic conditions, fermentation occurs
    • In humans, produces lactic acid
    • In other organisms, might produce alcohol/ethanol
  • With oxygen, proceeds to Krebs Cycle and then ETC
  • Most ATP is produced in the ETC using intermediates from glycolysis and Krebs Cycle

Glycolysis Details

  • Substrates and Products:
    • Starts with glucose (C₆H₁₂O₆)
    • Ends with two pyruvate molecules (or pyruvic acid)
  • Phases of Glycolysis:
    1. Investment Phase:
    • Uses 2 ATP to start the process
    • Glucose is broken into two 3-carbon molecules with phosphate groups (phosphoglyceraldehyde or PGAL)
    1. Payoff Phase:
    • Each 3-carbon molecule is converted to pyruvate
    • Generates 4 ATP and 2 NADH, net gain of 2 ATP (since 2 ATP were used in investment phase)

Summary of Glycolysis Reaction

  • Start with:
    • Glucose (C₆H₁₂O₆)
    • 2 ATP
    • 2 NAD⁺
    • 4 ADP + 4 Pi (phosphate groups)
  • End with:
    • 2 Pyruvates
    • 2 NADH
    • 4 ATP (net gain of 2 ATP)

Major Points to Remember

  • Glycolysis occurs in the cytoplasm
  • Two ATP molecules are used initially (Investment Phase)
  • Four ATP molecules and two NADH molecules are produced (Payoff Phase)
  • Net gain: 2 ATP and 2 NADH from one glucose molecule
  • Pyruvate molecules proceed to further stages of cellular respiration (Krebs Cycle and ETC) if oxygen is present
  • Under anaerobic conditions, pyruvate undergoes fermentation
  • NADH produced in glycolysis can be used later in ETC to produce more ATP

Biochemical Reactions and Intermediates

  • Initial breakdown involves phosphorylation of glucose
  • Isomerization steps produce two 3-carbon sugars (PGAL)
  • Conversion of PGAL to Pyruvate produces NADH and ATP
  • Important intermediates: Glyceraldehyde-3-phosphate (G3P)/PGAL, 1,3-Bisphosphoglycerate, 3-Phosphoglycerate, Phosphoenolpyruvate (PEP), Pyruvate

Key Takeaways

  • Glycolysis is the first step in cellular respiration and crucial for ATP production
  • Can proceed in both aerobic and anaerobic conditions
  • Ensures the breakdown of glucose into usable cellular energy form (ATP)
  • Generates intermediates (NADH, Pyruvate) essential for subsequent energy-producing processes