Topic_6_and_7_Notes(Unit3)

Cellular Respiration

Overview

  • Cells convert chemical energy stored in organic molecules into ATP.

  • General equation:

    • Organic molecules + O2 → CO2 + H2O + energy.

  • Primary fuel for animals is starch, which breaks down into glucose (C6H12O6).

Mitochondria Structure

  • Review the structures of mitochondria: outer membrane, inner membrane, intermembrane space, and matrix.

Chemical Process

  • Catabolic breakdown of glucose

    • Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP + heat

    • Oxidation: glucose loses electrons.

    • Reduction: oxygen gains electrons.

    • Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain) or LEO goes GER (Lose Electrons Oxidation, Gain Electrons Reduction).

Electron Pathway in Energy Harvest

  • Electrons follow the pathway: glucose → NADH → Electron Transport Chain (ETC) → O2.

Stages of Cellular Respiration

  • Three main stages:

    1. Glycolysis

    2. Pyruvate Oxidation and Citric Acid Cycle

    3. Oxidative Phosphorylation

Glycolysis

  • Initial step; occurs in the cytosol.

  • Converts glucose (6-carbons) into 2 pyruvate (3-carbons).

  • Summary pathway:

    • Glucose → 2 pyruvate + 2 ATP + 2 NADH.

  • Two stages:

    • Energy Investment Stage: Uses ATP to phosphorylate glucose derivatives.

    • Energy Payoff Stage: Produces ATP and NADH through substrate-level phosphorylation.

Pyruvate Oxidation and Citric Acid Cycle

  • Occurs in mitochondria when oxygen is present.

  • Pyruvate Oxidation:

    • Converts pyruvate into Acetyl CoA, producing CO2 and NADH.

  • Citric Acid Cycle (Krebs Cycle):

    • Occurs in the mitochondrial matrix, produces ATP, NADH, FADH2, and CO2 from Acetyl CoA.

    • Inputs: 2 Acetyl CoA; Outputs: 2 ATP, 6 NADH, 2 FADH2, 4 CO2.

Oxidative Phosphorylation

  • Comprises of the Electron Transport Chain (ETC) and Chemiosmosis.

  • Electron Transport Chain:

    • Located in the inner mitochondrial membrane; transfers electrons, pumps protons (H+) to create a gradient.

    • Final electron acceptor is oxygen, forming water.

  • Chemiosmosis:

    • ATP synthase uses the H+ gradient to convert ADP + P into ATP.

    • Produces approximately 26-28 ATP per glucose.

Energy Yield Summary

  • Glycolysis Total Yield: 2 ATP, 2 NADH.

  • Pyruvate Oxidation Total Yield: 2 NADH.

  • Citric Acid Cycle Total Yield: 2 ATP, 6 NADH, 2 FADH2.

  • Oxidative Phosphorylation Yield: 26-28 ATP.

  • Total ATP yield per glucose: 30-32 ATP.

Fermentation and Anaerobic Respiration

  • Without oxygen, organisms rely on:

    • Anaerobic Respiration: Uses an ETC without oxygen (final electron acceptors: sulfates or nitrates).

    • Fermentation: Generates ATP without an ETC, recycles NAD+. Types include:

      • Alcohol Fermentation: Converts pyruvate to ethanol (e.g., yeast).

      • Lactic Acid Fermentation: Converts pyruvate to lactate (e.g., muscle cells during intense exercise).

    • Excessive lactate can lead to lactic acidosis if not broken down in the liver.

Key Concept Checks

  1. Glycolysis occurs in the cytosol; produces pyruvate and 2 ATP.

  2. Citric Acid Cycle occurs in the mitochondrial matrix; produces 2 ATP.

  3. Final electron acceptor in ETC is oxygen, which is essential for ATP production.