Ap Bio: Unit 3: Enzyme Stuff

Topic 3.1: Enzyme Structure

  • Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

  • Structure: Enzymes are proteins with a specific 3D shape, including an active site where the substrate binds.

  • Substrate specificity: The enzyme's active site is complementary in shape to its substrate, fitting like a "lock and key."

  • Induced fit model: The enzyme slightly changes shape to better fit the substrate when binding occurs.

Topic 3.2: Enzyme Catalysis

  • Enzyme-substrate complex: The intermediate formed when an enzyme binds to its substrate.

  • Activation energy: The energy required for a reaction to occur. Enzymes lower the activation energy.

  • Reaction rate: Measured by the change in product concentration over time.

  • Effects of inhibitors:

    • Competitive inhibition: Inhibitor competes with the substrate for the active site. Can be overcome by increasing substrate concentration.

    • Non-competitive inhibition: Inhibitor binds to an allosteric site (not the active site), changing enzyme shape and decreasing its activity.

Lab Investigation:

  • Enzyme activity can be studied by measuring how fast substrates are consumed or products are formed (e.g., catalase breaking down hydrogen peroxide into water and oxygen).

Topic 3.3: Environmental Impacts on Enzyme Function

  • Environmental conditions can alter enzyme shape and function:

    • Temperature: Extreme temperatures can denature enzymes, while optimal temperatures increase reaction rates.

      • inc in temp outside optimum range will inc activity, then later denature

      • dec in temp outside optimum range will slow activity, never denature

    • pH: Enzymes work best within a specific pH range. Too acidic or basic environments can disrupt bonds in the enzyme, leading to denaturation.

      • if outside optimum range → dec in enzyme activity, later denatured

    • Salt concentration (Salinity): Ionic conditions affect enzyme structure. Too much or too little can disrupt bonding in the enzyme's structure.

    • Enzyme Concentration:

      • inc → inc activity

      • dec → dec activity

    • Substrate Concentration:

      • inc will inc, and later stay constant to a certain point

Denaturation and Cofactors/Coenzymes

  • Denaturation is the irreversible process of an enzyme losing its shape and, consequently, its function due to environmental changes (like heat or pH).

  • Changes in shape cause denaturation

    • active site can no longer bind to specific substrate

    • denaturation can be reversible in some cases

  • Cofactors and coenzymes (non-protein helpers that assist enzyme function)

    • Cofactors- Inorganic cofactors

      • Consists of metals

      • Holoenzyme : An enzyme with the cofactor attatched

    • Coenzymes- Organic cofactors

      • ex: vitamins

Topic 3.4: Cellular Energy

  • Energy in Cells:

    • Cells use energy for processes like growth, repair, and maintenance.

    • ATP (Adenosine triphosphate) is the main energy currency of the cell.

    • ATP stores energy in its phosphate bonds and releases energy when it's hydrolyzed to ADP (adenosine diphosphate) and an inorganic phosphate.

  • Energy Coupling:

    • Cells couple exergonic reactions (release energy) with endergonic reactions (require energy).

      • Exergonic- “Downhill reaction, SPONTANEOUS, releases energy (Catabolic) (Degradation) (AB —> A+B+Energy)

      • Endergonic- “Uphill” reaction, REQUIRES ACTIVATION ENERGY, absorbs energy (Synthesis/Anabolic) (A+B —> AB)

  • Metabolism:

    • Catabolic pathways: Break down molecules and release energy (e.g., cellular respiration).

    • Anabolic pathways: Build molecules and require energy (e.g., photosynthesis).

Energy

  • Kinetic Energy- Energy associated with motion

    • Thermal Energy- Energy associated with the movment of atoms or molecules

  • Potential Energy- Energy that is stored

    • Chemical Energy- Potential energy available for release in a chemical reaction

Thermodynamics in Biology:

  • First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

  • Second Law of Thermodynamics: Every energy transfer increases the entropy (disorder) of the universe.

    • During energy transfers or transformations, some energy is unusable and often lost as heat