2–4 Chemical Reactions and Enzymes Photo Credit: Richard Megna/Fundamental Photographs Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Chemical Reactions Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Chemical Reactions The elements or compounds that enter into a chemical reaction are known as reactants. The elements or compounds produced by a chemical reaction are known as products. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Energy in Reactions Energy Changes Chemical reactions that release energy often occur spontaneously. These are exergonic reactions. Chemical reactions that absorb energy will not occur without a source of energy. These are endergonic reactions. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Energy in Reactions When hydrogen gas reacts with oxygen to produce water vapor, it is an energy-releasing reaction in which energy is given off as heat. 2H2 + O2 2H2O How would you reverse this reaction? Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Cellular respiration is the process through which organisms energy from food. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Energy in Reactions Activation Energy Chemists call the energy that is needed to get a reaction started the activation energy. Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will occur only with a source of energy. The peak of each graph represents the energy needed for the reaction to go forward. The difference between this required energy and the energy of the reactants is the activation energy. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Enzymes Enzymes Some chemical reactions that make life possible are too slow or have activation energies. These chemical reactions are made possible by catalysts. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Catalysts Catalysts are substances that make chemical reactions happen faster. Enzymes are biological catalysts. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Enzymes Enzymes speed up chemical reactions that take place in cells. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Enzyme Action The Enzyme-Substrate Complex Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction. The reactants of enzyme-catalyzed reactions are known as substrates. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Enzyme Action An Enzyme-Catalyzed Reaction The enzyme hexokinase converts the substrates glucose and ATP into glucose-6-phosphate and ADP. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall Enzyme Action Regulation of Enzyme Activity Enzymes can be affected by any variable that influences a chemical reaction. pH values Changes in temperature Enzyme or substrate concentrations Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 The elements or compounds produced by a chemical reaction are known as reactants. enzymes. products. waste. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 Chemical reactions always involve changes in energy. enzymes. catalysts. changes in the atomic number of the reactants. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 The factor that prevents many energy-releasing reactions from occurring at relatively low temperatures is called catalytic energy. chemical bond energy. enzyme energy. activation energy. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 Which of the following statements is true? All proteins are enzymes. All catalysts are enzymes. All enzymes are catalysts. All catalysts are proteins. Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall 2–4 What happens to an enzyme after the reaction it catalyzes has taken place? The enzyme is destroyed, and the cell must make another. The enzyme holds on to the product until another enzyme removes it. The enzyme is unchanged and ready to accept substrate molecules. The enzyme changes shape so it can accept a different kind of substrate. Copyright Pearson Prentice Hall
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