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=rate of reaction at Trate of reaction at T+10∘C
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.