Cellular Energetics Notes

Introduction

• Transition from personal anecdote about hair to cellular energetics as the main focus.

• Key topics: enzymes, photosynthesis, and respiration.

Energy in Biology

• Three important types of energy:

• Kinetic Energy:

  • Energy of movement; anything moving has kinetic energy.

• Heat Energy:

  • Energy associated with temperature; higher temperatures mean higher energy (example: rubbing hands together to generate heat).

• Chemical Energy:

  • Energy stored in molecular bonds; a form of potential energy that cells use to do work.

  • Concept similar to lifting a book: potential energy is stored until used.

Thermodynamics

• The study of energy transfer.

• Laws of Thermodynamics:

• First Law: Conservation of energy; energy cannot be created or destroyed, only transformed.

• Second Law: Entropy (disorder) in the universe is always increasing; even if local order increases, overall disorder grows (example: ice melting into water).

• Fundamental Equation: $\Delta G = \Delta H - T \Delta S$

  • $\Delta G$ : Change in Gibbs Free Energy; indicates how much energy a cell can use.

  • $\Delta H$ : Enthalpy; total energy.

  • $\Delta S$: Entropy.

• Spontaneity:

• If $\Delta G > 0$, reaction is non-spontaneous (requires energy input).

• If $\Delta G < 0$, reaction is spontaneous (energy is released).

ATP and Reaction Coupling

• ATP (Adenosine Triphosphate): Main energy carrier in cells.

• ATP releases energy when a phosphate bond is broken; this process is exergonic.

• Coupling exergonic reactions with endergonic ones allows cells to do work effectively.

Enzymes

• Biological catalysts that speed up reactions without being consumed.

• Activation Energy: The energy required to initiate a reaction; enzymes lower this energy barrier.

• Active site: Part of the enzyme that binds substrates.

• Factors affecting enzymes: Temperature and pH can influence enzyme activity; extremes can denature enzymes (alter their structure).

• Inhibition Types:

  • Competitive Inhibition: Another molecule competes for active site.

  • Non-Competitive Inhibition: Binds elsewhere, altering enzyme's function without blocking the active site.

  • Feedback Inhibition: End product of a reaction inhibits an enzyme involved in its production when levels are high.

Respiration

• Describes the process by which glucose is broken down with oxygen to yield ATP.

• Cellular respiration equation:
  $C6H{12}O6 + O2 \rightarrow CO2 + H2O + ATP$

• Steps of respiration:

1. Glycolysis: Breaking down glucose into pyruvate (2 ATP, 2 NADH produced).

2. Pyruvate Oxidation: Converts pyruvate to acetyl-CoA; releases CO2.

3. Krebs Cycle: Further breakdown of acetyl-CoA, producing ATP and more NADH.

4. Electron Transport Chain (ETC): Uses electrons from NADH to create a proton gradient that generates ATP through chemiosmosis (oxidative phosphorylation).

• Fermentation: An anaerobic process where glycolysis occurs to produce ATP without using oxygen, recycling NADH to NAD+.

Photosynthesis

• Process used by autotrophs to convert light energy into chemical energy stored in glucose.

• Photosynthesis equation:
  $6CO2 + 6H2O + light \rightarrow C6H{12}O6 + 6O2$

• Two main stages:

1. Light-Dependent Reactions: Convert light energy into ATP and NADPH (involves electron transport chain similar to respiration).

2. Calvin Cycle: Uses ATP and NADPH to fix carbon dioxide into glucose.

• Different adaptations of plants (e.g., C4 plants, CAM plants) to deal with photorespiration or CO2 fixation in challenging environments.

Molecular Variation

• Discusses how organisms adapt their molecules (e.g., different chlorophyll types) for changing environmental conditions.

Conclusion

• Summary of major concepts in cellular energetics: energy forms, thermodynamics, ATP, enzymes, respiration, and photosynthesis.