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Overview of Cellular Respiration and Glycolysis

Mar 15, 2025

Cellular Respiration and Glycolysis Overview

Key Phases of Cellular Respiration

  1. Glycolysis
    • Occurs with or without oxygen.
    • Without oxygen: leads to fermentation (produces lactic acid in humans, alcohol in other organisms).
    • With oxygen: proceeds to the Krebs (Citric Acid) Cycle and the Electron Transport Chain.
  2. Krebs Cycle (Citric Acid Cycle)
    • Requires oxygen.
    • Produces raw materials for the Electron Transport Chain.
  3. Electron Transport Chain (ETC)
    • Major site of ATP production.
    • Uses materials from Glycolysis and Krebs Cycle.

Focus: Glycolysis

  • Starting Material: Glucose (C6H12O6)
  • End Product: Pyruvate (also known as pyruvic acid)

Phases of Glycolysis

1. Investment Phase

  • ATP Usage: Uses 2 ATP molecules.
  • Process: Glucose is broken into two 3-carbon molecules, each with a phosphate group.
  • Intermediate Molecule: Phosphoglyceraldehyde (PGAL or Glyceraldehyde 3-phosphate).

2. Payoff Phase

  • Conversion: Each PGAL is converted into pyruvate.
  • ATP Production: Produces 4 ATP molecules (2 ATPs per PGAL).
  • NADH Production: Each PGAL produces NADH from NAD+, important for later ATP production in ETC.

Net Production from Glycolysis

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

Glycolysis Reaction Summary

  • Inputs:
    • 1 Glucose
    • 2 NAD+
    • 2 ATP
    • 4 ADP
    • 4 Phosphate groups
  • Outputs:
    • 2 Pyruvate
    • 2 NADH
    • 2 Net ATP
    • 2 ADP
    • 4 ATP (gross production)

Key Concepts

  • Oxidation in Glycolysis:
    • Glucose is oxidized; its electrons are hogged by oxygen, leading to formation of pyruvate.
  • ATP Generation:
    • Direct ATP generation in glycolysis through substrate-level phosphorylation.

Importance of NADH

  • Function: NADH serves as an electron carrier that can produce additional ATP (approx. 3 ATP per NADH) in the Electron Transport Chain.

This overview of glycolysis provides a simplified understanding of the process, emphasizing the key phases and net production. The mechanism, while complex, reveals the transformation of glucose into energy currency for the cell.

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