Protein Functions 5.3, 5.5-5.9

5.3 Chemical reactions either store or release energy Endergonic reactions Require an input of energy from the surroundings Yield products rich in potential energy Energy is ABSORBED Example: photosynthesis

Amount of energy required LE 5-3a Products Amount of energy required Energy required Potential energy of molecules Reactants

Exergonic reactions Release energy Yield products that contain less potential energy than their reactants Examples: cellular respiration, wood burning

Amount of energy released LE 5-3b Reactants Amount of energy released Energy released Potential energy of molecules Products

Cells carry out thousands of chemical reactions, which constitute cellular metabolism Energy coupling uses energy released from exergonic reactions to drive endergonic reactions

HOW ENZYMES FUNCTION 5.5 Enzymes (types of proteins) speed up the cell's chemical reactions by lowering energy barriers Energy of activation Amount of energy that must be input before an exergonic reaction will proceed (the energy barrier)

Enzymes Proteins that function as biological catalysts Increase the rate of a reaction without themselves being changed An enzyme can decrease the energy of activation needed to begin a reaction

LE 5-5b enzyme enzyme EA without EA with Reactants Energy Net change in energy Products Progress of the reaction

5.6 A specific enzyme catalyzes each cellular reaction Each enzyme has a unique three-dimensional shape that determines which chemical reaction it catalyzes Substrate: a specific reactant that an enzyme acts on Active site: A pocket on the enzyme surface that the substrate fits into

Animation: How Enzymes Work Induced fit: The way the active site changes shape to "embrace" the substrate A single enzyme may act on thousands or millions of substrate molecules per second Animation: How Enzymes Work

LE 5-6 Enzyme available with empty active site Active site Substrate (sucrose) Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose Fructose H2O Products are released Substrate is converted to products

5.7 The cellular environment affects enzyme activity Physical factors influence enzyme activity Temperature, salt concentration, pH Some enzymes require nonprotein cofactors Metal ions, organic molecules called coenzymes

5.8 Enzyme inhibitors block enzyme action Inhibitors interfere with an enzyme's activity A competitive inhibitor takes the place of a substrate in the active site A noncompetitive inhibitor alters an enzyme's function by changing its shape In feedback inhibition, enzyme activity is blocked by a product of the reaction catalyzed by the enzyme

Normal binding of substrate LE 5-8 Substrate Active site Enzyme Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition

CONNECTION 5.9 Many poisons, pesticides, and drugs are enzyme inhibitors Cyanide inhibits an enzyme involved with ATP production during cellular respiration Some pesticides irreversibly inhibit an enzyme crucial for insect muscle function Many antibiotics inhibit enzymes essential for disease-causing bacteria Ibuprofen and aspirin inhibit enzymes involved in inducing pain