Enzymes Chapter 6

What Are Enzymes? Catalysts- substances that speed up a reaction Enzymes – biological catalysts Proteins Reactions are too slow; need to speed up in order to maintain life

Reactions For reactions to energy barrier must be overcome Exergonic reactions proceed only after the reactants are pushed over energy barrier Ex: Propane + oxygen Need to have a spark to start reaction Pushed over energy barrier Activation Energy (Ea) The amount of energy needed to start the reaction

Activation Energy (Ea) Amount of energy needed to start the reaction Transition-state species: Energy needed to change reactants into unstable molecular forms Chemical bonds stretch & become unstable Activation energy can come from reactants kinetic energy from motion Does not work in living systems Enzymes lower the energy barrier by bringing the reactants together.

Enzymes ENZYMES lower the energy barrier Bring the reactants into close proximity to each other Biological catalysts are highly specific Enzyme recognizes & binds to only one or a few closely related reactants Names of enzymes represent their function & usually end in “-ase”

Enzymes Substrates Active Site Enzyme-Substrate Complex (ES) Reactants in enzyme-catalyzed reaction Active Site Where catalysis takes place Enzyme-Substrate Complex (ES) The binding of a substrate to the active site E + S ES E + P

How Enzymes Work Chemical interaction occur in the ES complex Break old bonds & form new ones Enzymes use the following mechanisms Enzymes orient substances Orient to ensure correct bonds are formed Enzymes induce strain in the substance Stretches the bonds to create unstable transition state Enzyme temporarily add chemical groups to substrates

How enzymes work Enzyme Contain hundreds of amino acids usually with a single fold Active site is quite small (6-12 amino acids) Helps select the right substrates Enzyme changes shape when substrates bind: induced fit Ensures the substrates are properly positioned

Enzymes Some enzymes require “partners” to function Prosthetic group Non-amino acids atoms or molecules that are permanently bound Cofactors Inorganic ions that bind to enzymes (essential to function) Copper, zinc, iron Coenzymes Required for certain actions of enzymes Carbon-containing atom Help add and/or remove chemical groups from substrates ATP & ADP are necessary for reactions; considered coenzymes Vitamins

Metabolic Pathway Metabolic Pathway Systems biology Chemical reactions that occur one right after the other Product of one is the reactant for the next Pathways are interconnected; helps maintain homeostasis Systems biology Study of metabolic pathways

Inhibitors Inhibitors Natural inhibitors Artificial inhibitors Slow down the rate of enzyme-catalyzed reactions Natural inhibitors Regulates metabolism Artificial inhibitors Treat diseases, kills pests

Inhibitors Irreversible inhibitors Reversible Covalently bonds permanently inactivating the enzymes Nerve gas Reversible Bonds non-covalently to active site Prevents substrates from bonding Competitive inhibitor Binds elsewhere causing enzyme to change shape & alter active site Noncompetitive inhibitor

Irreversible inhibitor

Reversible Inhibitor

Affects of enzyme activity Environment pH Each have an ideal pH Activity decreases the more acidic or basic a solution becomes Temperature High temperature non-covalent bonds break Enzymes denature

Isozymes: enzymes that catalyze the same reaction but have different properties, such as optimal temperature. Organisms can use isozymes to adjust to temperature changes. Enzymes in humans have higher optimal temperature than enzymes in most bacteria—a fever can denature the bacterial enzymes.