Aerobic Cellular Respiration

Aerobic Cellular Respiration

Overview

• Importance of Energy in Organisms

  • All organisms require energy for various daily activities and life processes including:

  • Growth

  • Repair

  • Reproduction

  • Muscle contraction

  • Nerve impulses

  • Chemical reactions (metabolism)

Energy Expenditure in Humans

• Typical Energy Distribution:

  • Lifestyle activities: 20-35%

  • Basal metabolic functions: 60-75%

  • Digestion of food: 5-10%

Energy Sources

• Types of Organisms:

  • Autotrophs: Organisms that make their own organic food (e.g., plants, some prokaryotes).

  • Heterotrophs: Organisms that must consume organic food (e.g., humans, animals, some prokaryotes).

• Energy Storage:

  • Energy contained within organic foods is stored in bonds, particularly glucose.

  • Energy in glucose must be converted into a usable form, typically ATP.

Aerobic Cellular Respiration Process

• Definition: The conversion of energy stored in organic food molecules into energy stored in ATP under aerobic conditions (presence of oxygen).

• General Reaction:

  • ext{C}6 ext{H}{12} ext{O}6 + 6 ext{O}2
    ightarrow 6 ext{CO}2 + 6 ext{H}2 ext{O} + ext{Energy} ext{ (ATP)}

• Key Points:

  • Aerobic: The term indicates the process occurs in the presence of oxygen.

  • Gibbs Free Energy Change ( ext{ΔG} = -686 ext{ kcal/mol}) indicates energy is released during the process.

ATP: Energy Currency of the Cell

• ATP (Adenosine Triphosphate):

  • Cells utilize ATP as the direct energy source, not glucose.

  • Energy release from ATP:

  • From the breakdown of glucose yields ext{ΔG} = +7.3 ext{ kcal/mol} per ATP.

Role of Mitochondria

• Location of ATP Production:

  • In eukaryotic cells, the majority of ATP production occurs in mitochondria, often referred to as the "cell's energy factories".

Redox Reactions in Cellular Respiration

• Basics of Redox Reactions:

  • In redox (reduction-oxidation) reactions, electrons are transferred between molecules.

  • Key Definitions:

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

  • Example: ext{A}e^- + ext{B}
    ightarrow ext{A} + ext{Be}^-

  • Mnemonics: OIL RIG (Oxidation is Loss, Reduction is Gain)

Electron Transport and Carriers

• Hydrogen as a Carrier:

  • Electrons are transferred as part of hydrogen atoms

  • ext{H} = e^- + ext{H}^+

• Role of Electron Carriers:

  • Store and transfer electrons, crucial for cellular respiration.

  • Types include:

  • Nicotinamide adenine dinucleotide (NAD+): Oxidized form; ext{NADH}: Reduced form (addition of hydrogens).

  • Flavin adenine dinucleotide (FAD): Oxidized form; ext{FADH}_2: Reduced form.

Stages of Aerobic Cellular Respiration

1. Glycolysis (Occurs in Cytosol - Anaerobic)

   • Phases:

     • Energy investment phase

     • Energy pay-off phase

   • Net Reaction:

     • ext{Glucose}
       ightarrow 2 ext{Pyruvate}

     • 2 ext{ADP} + ext{Pi}
       ightarrow 2 ext{ATP}

     • 2 ext{NAD}^+
       ightarrow 2 ext{NADH}

2. Conversion of Pyruvate to Acetyl CoA (Occurs in Matrix of Mitochondria)

   • Net Reaction:

     • 2 ext{Pyruvate}
       ightarrow 2 ext{Acetyl CoA} + 2 ext{CO}_2

     • 2 ext{NAD}^+
       ightarrow 2 ext{NADH}

3. Citric Acid Cycle (Krebs Cycle)

   • Per 2 Acetyl CoA:

     • 2 ext{Acetyl CoA}
       ightarrow 4 ext{CO}_2

     • 2 ext{ADP} + ext{Pi}
       ightarrow 2 ext{ATP}

     • 6 ext{NAD}^+
       ightarrow 6 ext{NADH}

     • 2 ext{FAD}
       ightarrow 2 ext{FADH}_2

   • Glucose is completely oxidized to CO2, energy transferred to ATP, NADH, and FADH2.

4. Oxidative Phosphorylation (Electron Transport Chain and ATP Synthesis)

   • Role of electron carriers (NADH and FADH2) in donating electrons.

   • Oxygen as terminal electron acceptor forming water.

   • Creation of an electrochemical gradient across the inner mitochondrial membrane through H+ ions.

ATP Production Mechanism

• ATP Synthase and Chemiosmosis:

  • ATP synthase uses the H+ electrochemical gradient to synthesize ATP from ADP and Pi.

  • Chemiosmosis refers to this process of ATP synthesis driven by an H+ gradient.

  • Each complete turn of ATP synthase generates 3 ATP.

Other Metabolic Pathways

• Fermentation:

  • Occurs in absence of oxygen.

  • Two types:

    • Lactic Acid Fermentation: e.g., in humans and some bacteria, produces 2 lactate and 2 ATP.

    • Ethanol Fermentation: e.g., in plants and yeast, produces 2 ethanol, 2 CO2, and 2 ATP.

• Anaerobic Cellular Respiration:

  • Uses molecules other than oxygen as terminal electron acceptors.

  • Example: Some E. Coli strains utilize nitrate (NO3-) instead of oxygen.

Comparative Analysis of Cellular Respiration

• Types of Cellular Respiration:

  • Aerobic Cellular Respiration: Oxygen present, produces a large amount of ATP.

  • Fermentation: Absence of oxygen, very small ATP production (lactate or ethanol and CO2).

  • Anaerobic Cellular Respiration: Little oxygen available, variable ATP production based on other acceptors.