Unit 3 - Cellular Energetics Exam Preparation Notes

Enzymes

• Definition: Proteins that act as biological catalysts.

  • Function: Lower activation energy of chemical reactions.

• Active Site: The specific region where substrates bind and reactions occur.

• Substrate: The reactant that an enzyme acts on in a reaction.

• Conformational Change: Alteration in enzyme shape can affect reaction rate (often decreases it).

• Benefits: Enhances cellular efficiency and energy conservation.

• Factors Affecting Reaction Rate:

  • Extreme pH (acidic or basic) and high temperatures cause denaturation, reducing reaction rates.

  • Increasing enzyme or substrate concentration increases reaction rate.

  • Inhibitors:

  • Competitive Inhibitors: Bind to active site, preventing substrate binding.

  • Noncompetitive Inhibitors: Bind elsewhere, altering enzyme effectiveness.

Energy Input in Organisms

• Necessity of Energy: All organisms require continuous energy for survival. Lack of energy leads to death.

• Energy Coupling: Reactions requiring energy are paired with energy-releasing reactions, reducing waste.

Photosynthesis

• Definition: Process transforming carbon dioxide and water into glucose and oxygen using light energy.

• Reactions:

  • Reactants: Water, carbon dioxide, and light.

  • Products: Glucose and oxygen.

• Processes:

  1. Light Reactions:

  • Occur in thylakoid membranes.

  • Chlorophyll absorbs light, splits water producing electrons, hydrogen ions; oxygen released as waste.

  • Electrons flow through electron transport chain, creating a hydrogen ion gradient.

  • Gradient powers ATP synthase via chemiosmosis:

    • Produces ATP.

    • Generates NADPH, a high-energy electron carrier.

  1. Calvin Cycle:

  • Occurs in the stroma, using products from light reactions.

  • Carbon dioxide enters for reactions using ATP and NADPH energy.

  • Final product is glucose.

Cellular Respiration

• Definition: Process used by eukaryotic cells to produce energy.

• Reactions:

  • Reactants: Glucose and oxygen.

  • Products: Carbon dioxide, water, and ATP.

• Processes:

  1. Glycolysis:

  • Occurs in cytoplasm in all living cells.

  • Breaks glucose into two pyruvate molecules, producing ATP and NADH.

  1. Krebs Cycle:

  • Occurs in mitochondrial matrix.

  • Pyruvate undergoes reactions producing ATP, NADH, FADH2 (electron carriers), and carbon dioxide waste.

  1. Oxidative Phosphorylation:

  • Takes place in inner mitochondrial membrane.

  • NADH and FADH2 donate electrons to electron transport chain, establishing a hydrogen ion gradient.

  • Gradient fuels ATP synthase, generating most ATP in aerobic respiration.

Fermentation

• Definition: Alternative energy production process under anaerobic conditions (without oxygen).

• Types:

  1. Lactic Acid Fermentation:

  • Converts pyruvate into lactate/lactic acid, yielding small ATP amounts.

  1. Alcoholic Fermentation:

  • Converts pyruvate into ethanol and carbon dioxide, also producing small ATP amounts.

• Function:

  • Allows recycling of NADH, enabling glycolysis to continue despite lack of oxygen.