Enzymes Lecture Note

EnzymES Catalysis An enzyme is a globular protein which speeds up the rate of a chemical equation by lowering the activation energy (i.e. it is a biological catalyst) • Enzymes are not consumed by the reactions and can be re-used The molecule(s) the enzyme reacts with is called the substrate, which binds to a complementary region on the enzyme’s surface (active site) Active site Substrate Enzyme Specificity Lock and Key Model • Enzyme and substrate complement each other precisely in terms of both their shape and chemical properties • The active site and the substrate will share specificity Products Substrate Induced Fit Model • Active site is not a rigid fit for the substrate and changes its conformation to better accommodate the substrate • This stresses the substrate bonds and induces catalysis Products Substrate Catalysis Catalysis Factors Affecting Enzyme Activity Enzyme Kinetics Temperature • Increases enzyme activity (more kinetic energy = more collisions) • Enzyme activity peaks at an optimal temperature • Higher temperatures decrease activity (causes denaturation) The rate of enzyme catalysis can be increased by increasing the frequency of enzyme-substrate collisions (molecular motion) pH • Enzyme activity is highest at an optimal pH range • Activity decreases outside of this range (due to denaturation) Rate Rate Substrate Concentration • Increases enzyme activity (more particles = more collisions) • At a certain point, activity plateaus (saturation of active sites) Graph 2 Graph 1 Key: Rate Graph 1 – Temperature Graph 2 – pH level Graph 3 – Substrate level Graph 3 The rate of enzyme catalysis is decreased by denaturation Denatured Specificity Industrial Enzymes Immobilised enzymes are often used in industrial practices • They are fixed to a static surface to prevent enzyme loss • This improves separation of product and purity of yield One application for immobilised enzymes is the production of lactose-free milk and associated dairy products • Lactase (enzyme) digests lactose into glucose / galactose • Lactase is fixed to an inert surface (e.g. alginate beads) • Milk is passed over this surface to become lactose free There are several benefits associated with lactose-free milk: • Provides a source of dairy for lactose-intolerant people • Increases sweetness of milk (less need for sweeteners) • Reduces crystallization and production times for cheese