AP Bio unit 3

Structure and Function: Enzymes are biological catalysts made of proteins that speed up chemical reactions without being consumed.

Activation Energy: Enzymes lower the activation energy needed for reactions.

Active Site and Substrate: The enzyme’s active site binds to specific substrates, forming the enzyme-substrate complex.

Factors Affecting Enzyme Activity:

  • Temperature and pH: Extreme conditions can denature enzymes, altering their function.

  • Substrate Concentration: Higher concentrations generally increase reaction rates, but enzymes can become saturated.

  • Inhibitors:

    • Competitive Inhibition: Inhibitors bind to the active site.

    • Non-competitive Inhibition: Inhibitors bind elsewhere, changing the enzyme’s shape.

Cellular Respiration

  • Purpose: Harvest energy from organic molecules (like glucose) to produce ATP, the cell's energy currency.

  • Stages:

    1. Glycolysis: Occurs in the cytoplasm; glucose breaks down into 2 pyruvate molecules, yielding a net of 2 ATP and 2 NADH.

    2. Pyruvate Oxidation: Pyruvate enters the mitochondria and is converted into acetyl-CoA.

    3. Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix; produces 2 ATP, 6 NADH, 2 FADH2, and releases CO2.

    4. Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis): Occurs in the inner mitochondrial membrane; electrons from NADH and FADH2 are used to generate a proton gradient that powers ATP synthase, producing ~32 ATP.


  • Lactic Acid Fermentation: Occurs in muscle cells; produces lactic acid.

  • Alcohol Fermentation: Occurs in yeast; produces ethanol and CO2.

Photosynthesis

  • Purpose: Convert light energy into chemical energy in the form of glucose (in plants, algae, and some bacteria).

  • Stages:

    1. Light Reactions (Photophosphorylation): Occur in the thylakoid membranes; use light energy to produce ATP and NADPH, and release O2 from water.

    2. Calvin Cycle (Light-Independent Reactions): Occurs in the stroma; uses ATP, NADPH, and CO2 to produce glucose.

Energy and Metabolism

  • Metabolic Pathways: Series of chemical reactions in cells that build or break down molecules.

    1. Catabolic Pathways: Break down molecules to release energy (e.g., cellular respiration).

    2. Anabolic Pathways: Build molecules and consume energy (e.g., photosynthesis).

  • Laws of Thermodynamics:

    1. First Law (Conservation of Energy): Energy cannot be created or destroyed, only transferred or transformed.

    2. Second Law (Entropy): Energy transfers increase the disorder (entropy) of the universe.

ATP and Energy Coupling

  • ATP (Adenosine Triphosphate): Main energy currency of the cell.

  • Energy Coupling: ATP drives endergonic (energy-requiring) reactions by transferring a phosphate group, making the reaction more favorable.