1. Reactants and Products  A chemical reaction is the process by which atoms or groups of atoms in substances are reorganized into different substances  bonds are formed or broken.  Clues that a chemical reaction has taken place include the production of heat or light, and formation of a gas, liquid, or solid (a new substance). Chemical Reactions Chemical reaction Physical change

2. Chemical Equations  Chemical formulas describe the substances in the reaction and arrows indicate the process of change.  Reactants are the starting substances, on the left side of the arrow.  Products are the substances formed during the reaction, on the right side of the arrow.

3.  This equation shows cellular respiration -- a series of chemical reactions that require glucose and oxygen as reactants.  Glucose sugar molecules are broken down and the energy from its covalent bonds is released.  Carbon dioxide and water are produced.  In a chemical reaction, the atoms in the reactants are rearranged to form new compounds (products). A Chemical Equation Glucose from food Oxygen from air Carbon dioxide Water REACTANTSPRODUCTS + ENERGY

4. Balanced Equations  The law of conservation of mass states matter cannot be created or destroyed.  The number of atoms of each element on the reactant side must equal the number of atoms of the same element on the product side. Chemical Reactions This equation is balanced.

5. Energy is needed to form covalent bonds. Breaking covalent bonds releases energy.

6.  The activation energy is the minimum amount of energy needed for reactants to form products in a chemical reaction. Energy of Reactions Chemical Reactions ZA+B AB

7.  This reaction is exergonic and released heat energy (exothermic). Ex.: hand warm packs, metabolic reactions that warm up the body  The energy of the product is lower than the energy of the reactants. Chemical Reactions Z A+B AB

8.  This reaction is endergonic and absorbed heat energy (endothermic). Ex.: “ice” packs used in sports injuries  The energy of the products is higher than the energy of the reactants. Chemical Reactions A+B AB

9.  A catalyst is a substance that lowers the activation energy needed to start a chemical reaction. It does not increase how much product is made and it does not get used up in the reaction. Enzymes are biological catalysts; they are proteins. Enzymes Chemical Reactions & Enzymes A+B AB

10.  The reactants that bind to the enzyme are called substrates; enzymes are specific for their substrates/reactions.  The specific location where a substrate binds on an enzyme is called the active site. Chemical Reactions & Enzymes What determines the specificity of an enzyme?

11. Chemical Reactions & Enzymes  The active site changes shape and forms the enzyme- substrate complex, which helps chemical bonds in the reactants to be broken and new bonds to form.  Factors such as pH, temperature, and other substances affect enzyme activity.  All the chemical reactions happening inside an organism make up its metabolism  enzymes control metabolic reactions

12. Two Models of Enzyme Function Lock & Key – the enzyme’s active site has a shape that is specific for the substrate; the substrate “fits” like a key into the active site Induced Fit – as the substrate binds, the enzyme changes shape and the active site conforms to the substrate

13. Metabolic Reactions Anabolic reactions = building up organic molecules; usually endergonic Ex.: Synthesis / Condensation – putting together building blocks to make a larger molecule Catabolic reactions = taking apart organic molecules; usually exergonic Ex.: Digestion, breaking down proteins and other large molecules Which arrow represents an anabolic reaction? Catabolic reaction?

15. Link to Virtual Lab – Effect of Substrate Concentration and pH on Enzyme Activity: http://glencoe.mcgraw-hill.com/sites/dl/free/0078759864/383930/BL_11.html