Enzyme Activity and Factors Influencing It

Unit Three: Enzymes

• Enzymes are globular proteins with a uniquely shaped active site.
• Enzymes accelerate chemical reactions by lowering activation energy.
• Activation energy is the minimum energy needed for reactants to become products.
• Enzymes are biological catalysts, but remain unchanged by the reaction.
• All enzymes are proteins; however, not all biological catalysts are proteins (e.g., ribozymes are RNA molecules with catalytic activity).
• Globular proteins have unique tertiary structures which give them a unique shape.
• A catalyst speeds up a reaction, but the reaction itself is unaltered.
• Enzymes are the mediators of metabolism.
• Metabolism encompasses chemical and physical changes (including breakdown and synthesis) of molecules.
• Enzymes accelerate bond breaking (catabolism) and bond forming (anabolism) processes to sustain life.
• Enzyme-catalyzed reactions occur within the enzyme's active site (a pocket).
• The active site's structure is responsible for the enzyme's specificity.
• The substrate (molecule acted upon by the enzyme) binds to the active site, forming an enzyme-substrate complex.
• Binding often causes a conformational change (induced fit) in the active site facilitating catalysis.
• The enzyme-product complex dissociates to form enzyme and product.

Lesson Objectives

• Define enzymes and activation energy.
• Explain how enzymes work.
• Describe the catalysis reaction of enzymes, activities, and substrates,

Nature of Enzymes

• Enzymes are globular proteins with active sites.
• Enzymes accelerate reactions by lowering activation energy, converting reactants to products.
• Enzymes remain unchanged during reactions.
• Enzymes are specific for a particular reaction and are made up of amino acids linked together by peptide bonds.
• All globular proteins have unique tertiary structures which gives them a unique shape.

Enzyme Properties

• Enzymes are involved in the mediation of metabolism.
• Enzymes are physical and chemical properties, such as molecular weight, solubility, precipitation and denaturation.

Enzyme Denaturation

• Denaturation is the unfolding of a protein's structure, losing its active site.
• Denaturation occurs with high temperatures, extreme pH values or with heavy metals, causing the loss of enzyme activity.

Enzyme Properties & Functions

• Enzymes, as biocatalysts, speed up reactions without themselves being consumed.
• Enzyme activity depends on parameters like temperature, pH, and concentration of enzyme and substrate molecules.
• Enzymes work best at optimum temperatures and pH values.
• Enzymes show varying levels of activity as the temperature and pH increases or decreases from their optimum values and are likely to have decreased efficiency above or below the optimum values.
• The separation of enzymes is often done via solutions (aqueous or ethanol).

Types of Enzyme Specificity

• Substrate: Enzyme acts only on a particular substrate.
• Group: Enzyme acts only on molecules with a specific functional group (e.g., amino, phosphate or methyl).
• Bond/linkage: Enzyme acts on a particular type of chemical bond.
• Optical/stereochemical: Enzyme acts only on specific steric or optical isomers.
• Co-factor: Enzyme act on the substrate and co-factors.

Enzyme Classification

• Enzymes are categorized into six major classes based on the type of reaction they catalyze.
• Each class has subclasses, and enzymes are further divided into sub-subclasses, each enzyme has a number (e.g., EC 3.4.11.1), which indicates the class, subclass, sub-subclass and serial number for identifying.

Enzyme Kinetics

• Enzyme kinetics explores the rates of chemical reactions catalyzed by enzymes and the binding affinities of substrates, inhibitors, and maximal catalytic rates.
• Enzyme kinetics explains how enzymes speed up reactions by lowering the activation energy of reactants.
• The rates of reactions are determined by the concentrations of enzyme and substrates.
• The relationship between the rate of reaction and the concentration of substrate is presented by the Km (Michaelis constant).

Michaelis-Menten Model

• This model connects the rate of enzyme-catalyzed reaction ([V1]), substrate concentration ([S]), and two constants: Vmax and Km.
• Vmax is the maximum velocity/maximum rate of reaction.
• Km is substrate concentration at half-maximal velocity.
• Km represents the enzyme's affinity for the substrate—a lower Km indicates a higher affinity.

Effects of Inhibitor on Enzyme Kinetics

• Competitive: Inhibitor binds to the active site, competing with the substrate. This increases the Km, but no effect on the Vmax.
• Non-competitive: Inhibitor binds to an allosteric site, altering the enzyme's shape. This causes a decrease in Vmax but no effect on Km.
• Uncompetitive: Inhibitor binds only to the enzyme-substrate complex, reducing both Vmax and Km.

Enzyme Applications and Benefits of Industrial Uses

• Enzymes are widely used in food, feed, textile, papermaking, leather, cleaning products, pharmaceuticals, and other industrial settings to accelerate reactions.
• Enzymes facilitate reactions at lower temperatures than traditional methods, resulting in energy savings and environmental benefits (reduced CO2 emissions).
• Enzymes are also used in the improvement of feed digestion, prevention of indigestion, increasing biological availability of nutrients, and manufacturing certain medicines.
• Several types of enzymes with specific functions (e.g., cellulases, amylases, lipases, proteases, DNA polymerases) are used in the various industrial and biological contexts described.

Specific Enzyme Roles

• Catalase: Decomposes hydrogen peroxide into water and oxygen.
• Amylase: Breaks down starch into simpler sugars.
• Protease: Catabolizing protein into peptide.
• Lipase: Breaks down fats into fatty acids and glycerol

Factors Affecting Enzyme Action

• Temperature: Enzymes have an optimal temperature range.
• pH: Enzymes have an optimal pH range.
• Substrate concentration: Enzyme speeds up reactions at low to medium substrate concentrations, but the reaction rate levels off once all active sites are saturated.
• Enzyme concentration: Increasing enzyme concentration will increase the reaction rate but only up to a point until the substrate becomes the limiting factor.
• Activators: Substances that enhance or activate enzymatic effects in a process.
• Inhibitors: Substances that decrease or inhibit enzymatic effects in a process.
• End-products: Products at the end of a series of reactions that may inhibit further production via negative feedback.

This quiz explores the various factors affecting enzyme activity, including temperature, pH levels, and the concept of enzyme specificity. It also discusses the implications of enzyme denaturation and the significance of enzymatic catalysis compared to non-catalyzed reactions. Evaluate your understanding of how these variables interact within biological systems.