Enzymes

AICE Biology 2024 - 2025 Unit 3: Enzymes

What is an enzyme?

  • Enzymes are:

    • Globular proteins

    • Catalysts

    • Speed up the rate of chemical reactions

    • Left unchanged at the end of the reaction

    • Specific to their substrates

  • “Enzyme-substrate specificity”

  • Specificity is determined by the tertiary structure (shape and reactivity) of the “active site”

Location of enzymes

  • Intracellular enzymes

    • Function inside animal cells.

    • Example: Break down food in food vacuoles.

  • Extracellular enzymes

    • Secreted outside of the cell.

    • Example: Digestive enzymes that break down food outside the cell.

  • Nutrients from broken down food are absorbed into the cell.

Mode of action of enzymes

  • Enzymes lower the activation energy needed for reactions to occur, enabling faster reactions.

Enzyme active sites

  • The active site of an enzyme is a specific region where another molecule (or molecules) can bind.

The “Lock-and-key” hypothesis for enzyme activity

  • The substrate is complementary to the active site of the enzyme, fitting exactly into the site; this shows specificity for the substrate.

The “Induced fit” hypothesis for enzyme activity

  • Similar to the “lock and key” hypothesis, but the enzyme and/or substrate can slightly change shape to ensure a perfect fit.

Course of an enzyme-catalyzed reaction

  1. Substrate binds to active site.

  2. Formation of the enzyme-substrate complex.

  3. Catalysis occurs through:

    • Proximity and orientation.

    • Strain or distortion of substrates.

    • Creation of a favorable microenvironment.

    • Covalent catalysis.

  4. Formation of the enzyme-product complex.

  5. Release of product.

  6. Regeneration of active site.

Summary of enzyme activity

  • The process includes substrate engagement, the alteration of the enzyme's active site for better substrate fit, lowering the activation energy, product formation, release, and returning the active site to its original state.

Enzyme kinetics

  • Vmax (Maximum Rate): Maximum reaction rate when all active sites are occupied. This represents the "speed limit" of enzyme activity.

  • Km (Michaelis constant):

    • Defined as the substrate concentration at which the reaction rate is half of Vmax.

    • Measures the affinity of an enzyme for its substrate.

    • Low Km:

      • High affinity for substrate, works efficiently at lower concentrations.

    • High Km:

      • Low affinity for substrate; requires high concentration for efficiency.

Factors affecting enzyme activity

  • Enzyme concentration: Increased levels speed up reactions if substrate is available.

  • Substrate concentration: Rate increases until enzyme saturation (Vmax).

  • Temperature: Each enzyme has an optimum temperature (~40°C for humans); higher temperatures can cause denaturation.

  • pH: Each enzyme has an optimum pH; deviations can affect structure and function.

Optimal conditions for enzymes

  • Temperature graphs: Show variations in optimal conditions for different enzymes.

  • pH graphs: Illustrate optimal pH for specific enzymes (e.g., pepsin and trypsin).

Enzyme affinity graph analysis

  • Comparison of enzyme affinities based on substrate interaction.

    • Key to understanding efficiency in various conditions.

Michaelis-Menten constant (Km) assessment

  • Understanding Km to better grasp enzyme-substrate interactions and enzymatic efficiency.

Presentation of metabolic diseases

  • Key aspects include:

    • Disease mechanism (mutated enzyme, substrates, products, and pathway importance)

    • Diagnosis and symptoms

    • Treatment and management strategies

  • Select from diseases such as Hurler Syndrome, Gaucher Disease, Tay-Sachs, Fabry, and others; present within 10 minutes.