Chapter 6: Enzyme Review

Substrate Specificity of Enzymes

  • Substrate

    • Defined as the reactant that an enzyme acts upon.

  • Enzyme

    • Binds to its substrate with high specificity, resulting in the formation of an enzyme-substrate complex.

The Active Site

  • Active Site

    • Described as the region on the enzyme where the substrate binds.

    • Visual Representation:

    • Diagram (a) shows the relationship between substrate, active site, and enzyme.

Induced Fit of a Substrate

  • The concept of induced fit of a substrate involves:

    • The mechanism by which the active site of the enzyme undergoes a change in shape to better accommodate the substrate.

    • This adjustment brings the chemical groups of the active site into precise positions to catalyze the chemical reaction effectively.

  • Visual Representation:

    • Diagram (b) illustrates the enzyme-substrate complex entering the active site.

Catalysis in the Enzyme's Active Site

  • Catalytic Cycle of an Enzyme:

    • The process begins with the substrate entering the active site of the enzyme.

    • As the substrate binds, the enzyme changes shape slightly.

    • This forms the enzyme-substrate complex.

    • Subsequently, the products are formed and released, leading to the enzyme-products complex, followed by the products leaving the active site.

Protein Structure Revisited

  • Reference to Chapter 3 for detailed information on protein structure.

  • Key Points:

    • The 3-D shape of a protein is determined by the amino acid sequence of the polypeptide chain.

    • The active site residues (amino acids) are crucial for the enzyme's function, enabling binding to specific substrate(s).

  • Impact of Cellular Environment on Enzyme Function:

    • Suboptimal temperatures can lead to the denaturation of the enzyme, resulting in loss of shape and function.

    • Suboptimal pH levels can diminish the interaction between substrate and enzyme, potentially hindering binding.

Effects of Local Conditions on Enzyme Activity

  • The activity of an enzyme is influenced by multiple local conditions:

    • Ion concentrations: Variations can affect enzyme stability and function.

    • pH levels: Alterations can change the charge and shape of both the enzyme and substrate, impacting binding.

    • Temperature: Fluctuations can accelerate or inhibit enzymatic reactions.

    • Regulatory molecules: These can enhance or inhibit enzyme activity.

Effects of Temperature and pH

  • Each enzyme has:

    • An optimal temperature at which it functions most efficiently.

      • Example:

      • Optimal temperature for a thermophilic enzyme may differ greatly compared to a mesophilic enzyme.

    • An optimal pH determined by its environment:

      • Example: Pepsin (a stomach enzyme) has an optimal pH of around 1.5-2.0.

      • Example: Trypsin (an intestinal enzyme) functions best at around pH 7.5-8.5.

  • Graphical Representations:

    • Graph (a) displays rate of reaction in relation to temperature for different enzymes.

    • Graph (b) shows optimal pH for pepsin and trypsin.

Specific Localization of Enzymes Within the Cell

  • Enzymes within cells may be:

    • Grouped into complexes: Enhancing efficiency through proximity.

    • Incorporated into membranes: Involved in various membrane-associated reactions.

    • Contained inside organelles: For example, enzymes in mitochondria are critical for cellular respiration.

  • Diagram depicting Mitochondria:

    • Size: approximately 1 µm, illustrating their small but crucial role in metabolic processes.