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2.4 Chemical Reactions KEY CONCEPT Life depends on chemical reactions. 2.4 Chemical Reactions ! "Bonds break and form during chemical reactions. •" Chemical reactions change substances into different ones by breaking and forming chemical bonds. –" Reactants are changed during a chemical reaction. –" Products are made by a chemical reaction. 2.4 Chemical Reactions ! "Chemical reactions release or absorb energy. •" Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction. 2.4 Chemical Reactions •" Exothermic reactions release more energy than they absorb. •" Energy is Released. 2.4 Chemical Reactions •" Endothermic reactions absorb more energy than they release. –" Energy is absorbed 2.4 Chemical Reactions ! "Complete Work Sheet 2.4 •" Know the different between Endothermic and exothermic. 2.4 Chemical Reactions KEY CONCEPT Ch 2.5 Enzymes are catalysts for chemical reactions in living things. 2.4 Chemical Reactions ! "A catalyst lowers activation energy. •" Catalysts are substances that speed up chemical reactions. –" decrease activation energy –" increase reaction rate 2.4 Chemical Reactions ! "Enzymes allow chemical reactions to occur under tightly controlled conditions. •" Enzymes are catalysts in living things. –" Enzymes are needed for almost all processes. –" Most enzymes are proteins. 2.4 Chemical Reactions •" An enzyme’s structure allows only certain reactants to bind to the enzyme. –" substrates –" active site substrates (reactants) enzyme Substrates bind to an enzyme at certain places called active sites. 2.4 Chemical Reactions •" The lock-and-key model helps illustrate how enzymes function. –" substrates brought together –" bonds in substrates weakened Substrates bind to an enzyme at certain places called active sites. The enzyme brings substrates together and weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme. 2.4 Chemical Reactions ! "Question 2.5 1.How does a catalyst affect the activation energy of a chemical reaction? 2. Describe how the interaction between an enzyme and its substrate changes a chemical reaction. 4. Suppose that the amino acids that make up an enzyme’s active site are changed. How might this change affect the enzyme? 2.4 Chemical Reactions ! "Answers •" 1. a catalyst reduces the activation energy required to start the reaction. •" 2. An enzyme brings substrates close together so that they can react, and slightly alter (weaken) the Bonds with the substrates by changing the shapes of the molecules. •" 4. The substrates would likely not bond to the enzyme because the shape of the active site would change. 2.4 Chemical Reactions •" Disruptions in homeostasis can prevent enzymes from functioning. –" Enzymes function best in a small range of conditions. –" Changes in temperature and pH can break hydrogen bonds. –" An enzyme’s function depends on its structure.