E

A&P chapter 26 03/03/2025

Overview of Cellular Respiration

  • Definition: The process by which cells convert nutrients, especially glucose, into ATP (adenosine triphosphate).

  • Importance of Mitochondria: Mitochondria are known as the powerhouse of the cell, responsible for producing the majority of ATP through cellular respiration.

Types of Cellular Respiration

  • Aerobic Cellular Respiration:

    • Definition: Requires oxygen.

    • Location: Takes place in the mitochondria.

    • ATP Production: Efficiently generates ATP.

  • Anaerobic Cellular Respiration:

    • Definition: Occurs without oxygen.

    • ATP Production: Less efficient ATP generation and leads to the production of lactic acid in humans.

Key Concepts of ATP Production

  • ATP Hydrolysis: Breaking down ATP to ADP (adenosine diphosphate) releases energy for cellular processes.

  • Reversible Reactions: ATP can be converted back from ADP + Pi (inorganic phosphate) through cellular respiration.

  • Energy Levels: ATP > ADP > AMP (adenosine monophosphate); energy is higher in fully charged ATP.

Fuel Sources for ATP Synthesis

  • Macromolecules Used:

    • Carbohydrates

    • Proteins

    • Fats

  • Process: These macromolecules are broken down into smaller units to enter cellular respiration pathways and generate ATP.

    • Primary fuel source is usually glucose, but others can be used when necessary.

Process of Cellular Respiration

Main Steps

  1. Glycolysis:

    • Location: Cytoplasm.

    • Oxygen Requirement: None; anaerobic process.

    • Product: Converts one glucose molecule (C6H12O6) into two pyruvate molecules (C3H4O3) and produces a net gain of 2 ATP and 2 NADH.

    • Investment Phase: Invest 2 ATP to start the process.

    • Energy Yield: 4 ATP produced, net gain of 2 ATP after accounting for the initial investment.

  2. Transitional Step:

    • Location: Mitochondrial Matrix.

    • Process: Converts pyruvate into acetyl CoA (C2H3O), producing 2 NADH and releasing 2 CO2 as waste gases.

  3. Krebs Cycle (Citric Acid Cycle):

    • Location: Mitochondrial Matrix.

    • Process: For each acetyl CoA:

      • Generates 3 NADH, 1 FADH2, 1 ATP, and releases 2 CO2.

      • Each glucose yields a total of 6 NADH, 2 FADH2, and 2 ATP after two cycles (one for each acetyl CoA).

  4. Electron Transport Chain (ETC):

    • Location: Inner mitochondrial membrane.

    • Process: Uses NADH and FADH2 to create a proton gradient, which drives ATP synthase, generating ATP.

    • Yield: 34 ATP produced from oxidation of NADH and FADH2.

Final Products of Cellular Respiration

  • Overall Reaction:

    • Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP.

  • Efficiency: Typically, 36-38 ATP molecules are produced per molecule of glucose, depending on the type of cell and conditions.

Anaerobic Respiration and Lactic Acid Fermentation

  • Lactic Acid Production: Occurs during intense exercise when oxygen levels are low, leading to muscle fatigue.

  • Energy Yield: Only 2 ATP produced from glycolysis with no additional output through the Krebs cycle or ETC.

Summary of Cellular Respiration Steps and Yield

  • Total ATP per Glucose Breakdown:

    • Glycolysis: Net gain of 2 ATP.

    • Krebs Cycle: 2 ATP, 6 NADH, 2 FADH2.

    • ETC: Generates additional 34 ATP from NADH and FADH2.

Important Notes

  • Mitochondria's structure: Double membrane with an outer and inner membrane (surrounds the matrix) crucial for ATP production processes.

  • Heart muscle and other cells constantly require ATP, even at rest.