How Cells Obtain Energy

Lecture on How Cells Obtain Energy

Lecture Objectives

  • Define Energy

  • Understand Chemical Reactions

  • Explore ATP

  • Examine Cellular Respiration

Understanding Energy

  • Energy: Capacity to do work.

Types of Energy

  • Potential Energy: Stored energy due to position or structure.

  • Kinetic Energy: Energy of moving objects.

  • Heat: Energy transferred from one system to another that does not perform work; often seen as unusable energy.

Thermodynamics

Laws of Thermodynamics

  1. First Law: Conservation of Energy

    • Total energy in the universe remains constant and conserved.

    • Energy cannot be created or destroyed; it can only be converted from one form to another.

  2. Second Law: Law of Entropy

    • Energy conversions are not 100% efficient, with some energy lost as heat.

    • Entropy of a closed system will always increase.

Energy Transformations

  • Types of energy transformations:

    • Chemical Energy → Kinetic Energy

    • Light Energy → Chemical Energy

Energy Conversion Examples

  • Cellular Work: Kinetic energy of movement powered by ATP (Adenosine Triphosphate).

  • Waste Products: Generated energy conversion results in poor chemical energy forms (e.g., CO2, water).

Chemical Reactions and Energy

  • Oxidation Reactions:

    • Loss of electrons (e-), resulting in the release of energy; termed catabolic, exergonic, or "downhill" processes.

  • Reduction Reactions:

    • Gain of electrons, requiring energy; termed anabolic, endergonic, or "uphill" processes.

Cellular Respiration

  • Definition: Breakdown of chemical bonds in food molecules to release stored energy and produce ATP.

  • Characteristics:

    • An aerobic process (requires oxygen) occurring in every cell.

    • Series of metabolic steps involved.

Aerobic Cellular Respiration Equation

  • Chemical Equation:

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

    • Glucose + Oxygen → Carbon Dioxide + Water + Energy

  • Energy Efficiency: Up to 32 ATP molecules generated from one molecule of glucose.

Redox Reactions in Cellular Respiration

  • Reduction: Oxygen gains electrons (also gains hydrogen).

  • Oxidation: Glucose loses electrons (also loses hydrogen).

Overview of Energy Flow in Ecosystems

  • Sunlight → Photosynthesis → Glucose production → Cellular Respiration → Energy for cellular work.

  • Heat energy dissipates from the ecosystem.

ATP and Cellular Work

  • ATP: The primary energy currency of the cell; powers most energy-requiring cellular reactions.

  • ATP Turnover: A working muscle cell recycles up to 10 million ATP molecules per second via the ATP cycle.

Overview of Cellular Respiration Processes

  • Main pathways:

    • Glycolysis: Glucose is converted to 2 pyruvic acid, generating ATP.

    • Citric Acid Cycle: High-energy electrons are produced via carriers like NAD+ and FAD.

    • Electron Transport Chain: Further ATP production occurs through transfer of electrons.

Helper Molecules in Cellular Respiration

  • NAD+/NADH: Essential for oxidation and reduction reactions, carrying electrons.

  • FAD/FADH2: Another carrier that functions similarly to NAD+.

  • Both NADH and FADH2 play significant roles in energy harvesting processes during respiration.