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.