Untitled

ENZYMES

Mode of Action of Enzymes

3.1.1 Definition and Classification of Enzymes

• Enzymes are globular proteins that act as catalysts in biochemical reactions.
  • Intracellular Enzymes: Catalyze reactions inside cells.
  • Extracellular Enzymes: Secreted from cells to catalyze reactions outside cells.

3.1.2 Mechanism of Action

• The mode of action of enzymes involves:
  • Active Site: The specific region of the enzyme where the substrate binds.
  • Enzyme-Substrate Complex: The temporary complex formed when an enzyme binds to its substrate.
  • Lowering Activation Energy: Enzymes lower the activation energy of a reaction, thus facilitating the reaction at lower temperatures.
  • Enzyme Specificity:enzymes are specific to their substrates, which can be explained by:
  • Lock-and-Key Hypothesis: The idea that the substrate fits exactly into the active site of the enzyme.
  • Induced-Fit Hypothesis: The concept that the enzyme changes shape slightly to better fit the substrate once it binds.

3.1.3 Investigation of Enzyme-Catalyzed Reactions

• Experiments can be conducted to measure the rates of formation of products using:
  • Catalase: Catalyzes the breakdown of hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).
  • Amylase: Catalyzes the breakdown of starch into maltose.

3.1.4 Use of a Colorimeter

• A colorimeter can measure enzyme-catalyzed reactions that involve color changes by assessing the absorption of light at different wavelengths.

3.2 Factors Affecting Enzyme Activity

3.2.1 Investigate Effects of Various Factors

• Factors that affect the rate of enzyme-catalyzed reactions:
  • Temperature
  • pH (using buffer solutions)
  • Enzyme Concentration
  • Substrate Concentration
  • Inhibitor Concentration

3.2.2 Maximum Rate of Reaction (Vmax)

• The maximum rate of reaction (Vmax) is used to derive the Michaelis–Menten constant (Km), which compares enzyme affinity for substrates.

3.2.3 Effects of Inhibitors

• Reversible Inhibitors can be:
  • Competitive: Compete with substrate for the active site and can be displaced by increased substrate concentration.
  • Non-competitive: Bind to allosteric sites on the enzyme, altering enzyme shape without competing with the substrate.

3.2.4 Enzyme Immobilization

• Investigate the activity of an enzyme immobilized in alginate versus free enzyme in solution.
• Advantages of Immobilized Enzymes:
  • Reduced operational costs.
  • Ability to reuse the enzyme.
  • Increased temperature and pH tolerance due to confinement within alginate beads.

Enzyme Structure

• Primary Structure: Linear sequence of amino acids.
• Secondary Structure: Includes alpha helices and beta-pleated sheets.
• Tertiary Structure: The three-dimensional shape formed by the bending and folding of the polypeptide chain.
• Quaternary Structure: Complexes formed by multiple polypeptide chains, e.g., hemoglobin.

Intracellular and Extracellular Enzymes

• Intracellular Enzymes are synthesized and retained within the cell, found in structures like cytoplasm and mitochondria.
  • Example: Oxidoreductase.
• Extracellular Enzymes are produced and secreted from cells to catalyze external reactions.
  • Example: Digestive enzymes from pancreas, which work in the duodenum.

Detailed Examination of Enzyme Activity

Active Site Interaction

• Substrate: The reactant that enzymes act upon.
• Molecular Model of Catalase:
  • Catalase's active site allows for specific substrate interaction during enzyme-substrate complex formation.

Enzyme Properties

• Enzymes are:
  • Specific to certain reactions.
  • Not consumed in reactions.
  • Catalysts that significantly reduce activation energy, making reactions feasible at physiological conditions.
  • Demonstrate high turnover rates, reflecting the number of reactions catalyzed per unit time.

Lock and Key Hypothesis vs. Induced Fit

• Lock and Key Hypothesis: The enzyme's active site is a specific shape complementary to the substrate.
• Induced Fit Theory: The enzyme alters its shape to securely bind the substrate, enhancing interaction and lowering the energy required for reaction initiation.

Activation Energy

• Activation Energy (Eₐ): The minimum energy required for a chemical reaction to occur. Enzymes lower activation energy via:
  • Formation of an enzyme-substrate complex, facilitating bond breakage and new bond formation.

Investigation of Enzyme-Catalyzed Reactions

• Experimentation can include collecting and measuring gas produced, such as O₂ from catalase activity on H₂O₂.
  • A sample data collection over time can result in a plot representing reaction progress.

Effect of Factor Changes on Reaction Rates

Enzyme Concentration

• Increasing the enzyme concentration raises the initial rate of reaction until a saturation point where all substrate molecules are occupied.

Substrate Concentration

• The initial rate of reaction increases with substrate concentration until all active sites are occupied, achieving Vmax.

Colorimetric Analysis

• A colorimetric assessment measures the color intensity, correlating with substrate quantity in reactions, allowing for graphical analysis of reaction rates.

Effects of Environmental Factors on Enzyme Activity

Temperature Effects

• Reaction rates can be modeled by the Q10 formula: $Q10 = \frac{\text{rate of reaction at } T + 10^{\circ}C}{\text{rate of reaction at } T}$
  • As temperature rises up to an optimal point, reaction rates increase exponentially; beyond optimal temperature, enzymes denature.

pH Effects

• Enzyme activity is influenced by pH through the ionization of amino acids affecting enzyme structure. Buffers can mitigate pH fluctuations.

Cofactors and Their Role

• Cofactors: Non-protein compounds necessary for enzyme activity:
  • Prosthetic Groups: Permanently attached (e.g., heme with iron).
  • Coenzymes: Temporarily assist enzyme activity (e.g., NAD from niacin).

Inhibitors

• Inhibitors can hinder enzyme activity:
  • Competitive Inhibitors: Compete at the active site, reducing activity proportional to substrate concentration.
  • Non-Competitive Inhibitors: Cause shape alterations, impacting activity irrespective of substrate concentration.

Feedback Mechanisms in Enzyme Regulation

• End Product Inhibition: The increase in product concentration inhibits the enzyme, regulating further product formation, exemplifying feedback systems in metabolic pathways.

Vmax and Km

• Vmax: The maximal rate achieved by an enzyme when all active sites are occupied.
• Km (Michaelis-Menten Constant): The substrate concentration at which the reaction rate is half of Vmax, reflecting enzyme affinity; a lower Km indicates higher affinity.

Enzyme Immobilization Techniques

Practical Approaches

• Enzymes can be trapped in matrices like alginate beads, enhancing reuse and stability against temperature and pH variations.
  • Practical Activity: Mix sodium alginate with enzyme to form beads through ionic gelation upon contact with calcium chloride.

Advantages of Immobilized Enzymes

• Efficiency in operational usage, cost-effectiveness, and environmental tolerance, leading to broader applications in various biotechnological processes.