Ch 8

Chapter 8: Cellular Respiration

Overview of Cellular Respiration

  • Definition: Cellular respiration is a cellular process that breaks down nutrient molecules while producing ATP.

  • Requirements:

    • Consumes oxygen (O2)

    • Produces carbon dioxide (CO2)

    • Aerobic process: Oxygen is necessary for this process.

  • Glucose Breakdown:

    • Primarily involves the breakdown of glucose into CO2 and H2O.

    • Energy is extracted step-wise, allowing for efficient ATP production.

  • Enzymes:

    • Oxidation-reduction enzymes such as NAD+ and FAD act as coenzymes in the process.

Cellular Respiration Process

  • Entry of Reactants:

    • O2 from the air and glucose from food enters cells, producing H2O and CO2.

  • Mitochondria Function:

    • Mitochondria use energy from glucose to form ATP from ADP + P.

Breakdown of Glucose

  • Electron Transfer:

    • Electrons are removed from substrates and received by oxygen, which combines with H+ to become water.

    • Glucose is oxidized while oxygen is reduced.

Oxidation-Reduction Reactions

  • Definitions:

    • Oxidation: Loss of an electron.

    • Reduction: Gain of an electron.

    • These reactions occur simultaneously (OIL RIG: Oxidation Is Loss, Reduction Is Gain).

  • Example: In NaCl formation, sodium is oxidized and chlorine is reduced.

Role of Coenzymes: NAD+ and FAD

  • NAD+:

    • A key coenzyme in oxidation-reduction reactions.

    • Becomes oxidized when it gives up electrons and reduced when it accepts electrons.

  • FAD:

    • Another coenzyme similar to NAD+.

    • Accepts two electrons and two H+ ions to become FADH2.

Overall Equation for Aerobic Cellular Respiration

  • Chemical Equation:

    • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

Mitochondrion Structure and Function

  • Organizational Structure: Mitochondria are the organelles where cellular respiration takes place.

Overview of Aerobic Respiration

  • Glycolysis:

    • Breakdown of glucose into pyruvate occurs in the cytoplasm; ATP is formed without utilizing oxygen (anaerobic).

  • Preparatory Reaction:

    • Converts pyruvate into substances used in the citric acid cycle, releasing carbon dioxide.

  • Citric Acid Cycle:

    • Located in the mitochondrial matrix; produces NADH, FADH2, and releases CO2.

    • Completes the oxidation of glucose.

  • Electron Transport Chain and Chemiosmosis:

    • A series of reactions that produce a significant amount of ATP (32 or 34 ATP molecules).

Phases of Cellular Respiration

  1. Glycolysis:

    • Occurs in the cytoplasm; splits glucose into two molecules of pyruvate.

    • Generates a net gain of 2 ATP.

  2. Preparatory Reaction:

    • Converts pyruvate into acetyl-CoA for entry into the citric acid cycle.

  3. Citric Acid Cycle:

    • Produces NADH and FADH2, releases CO2, and generates ATP.

  4. Electron Transport Chain:

    • Receives electrons from NADH and FADH2, producing ATP through chemiosmosis.

Chemiosmosis

  • Process: Involves a high concentration of H+ in the intermembrane space, creating an electrochemical gradient.

  • ATP Synthase: Allows H+ ions to flow back into the mitochondrial matrix, driving ATP production from ADP and inorganic phosphate.

Aerobic vs Anaerobic Conditions

  • Oxygen Availability:

    • If O2 is unavailable, fermentation occurs (anaerobic process) leading to lactic acid or alcohol production from pyruvate.

  • Fermentation Types:

    • Alcoholic Fermentation: Carried out by yeasts, produces CO2 and ethyl alcohol.

    • Lactic Acid Fermentation: Occurs in bacteria and animal muscles under strenuous activity, producing lactic acid.

Inputs and Outputs of Fermentation

  • Inputs:

    • Glucose

  • Outputs:

    • 2 lactate (or alcohol and CO2) + 2 ATP (from 2 ADP and 2 inorganic phosphates)

  • Net Gain: 2 ATP

Advantages and Disadvantages of Fermentation

  • Advantages:

    • Provides quick ATP for muscular activity.

  • Disadvantages:

    • Toxic effects of lactate and alcohol; causes muscle fatigue.

    • Much less efficient than aerobic respiration (only 2 ATP per glucose compared to 36-38).

Photosynthesis and Cellular Respiration

  • Relationship:

    • Photosynthesis produces glucose and oxygen, which are utilized in cellular respiration, while respiration produces energy, CO2, and water.

  • Overall Equations:

    • Photosynthesis: 6 CO2 + 6 H2O + energy → C6H12O6 + 6 O2

    • Cellular Respiration: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy

Summary of Cellular Respiration Phases

  • Glycolysis: Glucose to pyruvate, occurring in cytoplasm.

  • Preparatory Reaction: Pyruvate to Acetyl-CoA.

  • Citric Acid Cycle: Forms NADH and FADH2, releasing CO2.

  • Electron Transport Chain: Produces 32-34 ATP through chemiosmosis using the H+ gradient.