Cellular Respiration and Fermentation

Cellular Respiration Overview

  • Living cells derive energy primarily through cellular respiration, utilizing oxygen and organic molecules produced by photosynthesis.
  • Chemical energy in organic molecules is converted into ATP, primarily powering cellular activities.

Catabolic Pathways

  • Catabolic pathways release energy by breaking down complex organic molecules (exergonic).
  • Three ATP synthesis methods:
    • Aerobic respiration: uses oxygen.
    • Anaerobic respiration: uses alternatives to oxygen, producing less ATP.
    • Fermentation: partially degrades sugars without oxygen (recycles NAD+).

Cellular Respiration Process

  • Cellular respiration includes both aerobic and anaerobic processes but typically refers to aerobic respiration.
  • Chemical equation for cellular respiration:
    C_6H_{12}O_6 + 6 O_2
    ightarrow 6 CO_2 + 6 H_2O + ext{Energy (ATP + heat)}

Redox Reactions

  • Redox reactions involve electron transfer, releasing energy from organic molecules to synthesize ATP.
  • Oxidation: loss of electrons; Reduction: gain of electrons (OIL RIG).

Stages of Cellular Respiration

  1. Glycolysis: breaks glucose into pyruvate (occurs in cytoplasm).
  2. Citric Acid Cycle (Krebs Cycle): completes glucose breakdown, generates NADH, FADH2, and ATP.
  3. Oxidative Phosphorylation: uses NADH and FADH2 to produce ATP via the electron transport chain and chemiosmosis.

Glycolysis

  • Glycolysis occurs in two phases:
    • Energy Investment Phase: ATP is consumed.
    • Energy Payoff Phase: ATP and NADH are produced.
    • Net gain: 2 ATP and 2 NADH per glucose molecule.

Citric Acid Cycle

  • Pyruvate converted to acetyl CoA before entering the cycle.
  • Generates 1 ATP, 3 NADH, and 1 FADH2 per turn.
  • Relays electrons to the electron transport chain (ETC).

Oxidative Phosphorylation

  • ETC pumps H+ ions into the intermembrane space, creating a proton motive force.
  • ATP synthase utilizes the H+ gradient for ATP production (chemiosmosis).

ATP Production Efficiency

  • Approximately 30-32 ATP generated per glucose via cellular respiration.

Fermentation and Anaerobic Respiration

  • Glycolysis couples with fermentation/anaerobic respiration to produce ATP without oxygen.
  • Fermentation types: lactate (in muscles) and alcohol (in yeast).

Metabolic Pathway Integration

  • Glycolysis and the citric acid cycle connect to other metabolic pathways (proteins, carbohydrates, fats).
  • Feedback inhibition regulates cellular respiration based on ATP levels, modulating enzyme activity for metabolic control.