Enzymes
What are enzymes? Enzymes are proteins (tertiary and quaternary structures) Act as a catalyst to accelerate reactions Not permanently changed in the process
Enzymes Are specific for what they catalyze Are reusable End in –ase Sucrase Lactase Maltase Substrate Enzyme Active site
How do enzymes work? Enzymes weaken bonds, lowering the activation energy for the reaction Enzyme lowers activation energy X Free energy Reactants Products Reaction progress
How do enzymes work? Without enzyme With enzyme Free energy of activation Free energy Reactants Products Reaction progress
Enzyme-substrate complex The substance (reactant) that an enzyme acts on is the substrate Enzyme Substrate
Induced fit A change in the shape of an enzyme’s active site induced by the substrate Substrate
Active site A restricted region of an enzyme molecule which binds to the substrate is the active site Enzyme Active site
Enzymes and reactions Enzyme without substrate (no reaction) Enzyme + Substrate Products H2O O2 (bubbles) Liver (Catalase enzyme) Cubes H2O2 + Hydrogen peroxide (Substrate)
Factors affecting enzyme activity Temperature pH Cofactors and coenzymes Inhibitors
Temperature and pH High temperatures are the most dangerous; they denature (unfold) enzymes Most enzymes prefer temperatures near normal body temperature and near neutral pH ~ 37.5°C pH of 6 to 8 Ionic salts also denature enzymes Egg with denatured proteins
Cofactors and coenzymes Inorganic substances (ie. zinc, iron) and vitamins are sometimes needed for proper enzymatic activity Example: Iron must be present in the quaternary structure of hemoglobin in order for it to pick up oxygen http://biomed.brown.edu/Courses/BI108/BI108_2005_Groups/10/webpages/introlink.htm
Enzyme inhibitors Competitive inhibitors are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site Enzyme Substrate Inhibitor
Enzyme inhibitors (Continued) Noncompetitive inhibitors are chemicals that do not enter the active site They bind to another part of the enzyme, changing the shape of the enzyme and altering the active site Substrate Inhibitor