1. Enzymes

2. Essential Questions  What happens to chemical bonds during chemical reactions?  How do energy changes affect whether a chemical reaction will occur?  Why are enzymes important to living things?

3. Everything that happens in an organism is based on chemical reactions A CHEMICAL REACTION is a process in which one set of chemicals is changed to other chemicals Some chemical reactions are slow, some fast Ex. burning vs. rusting

4. The REACTANTS are the substances present before a chemical reaction; the PRODUCTS are the substances present after a chemical reaction Ex. iron + oxygen produces rust; 4Fe + 3O 2 → 2Fe 2 O 3 Note that in chemical reactions, bonds in the reactants are broken, and bonds are formed in the products; the atoms are rearranged Ex. cells constantly produce CO 2 ; for it to be carried to the lungs the following reaction occurs CO 2 + H 2 O → H 2 CO 3 and when the H 2 CO 3 is carried by blood to the lungs, the following reaction occurs H 2 CO 3 → CO 2 + H 2 O

5. When chemical reactions occur, energy is either released (EXOTHERMIC) or absorbed (ENDOTHERMIC); exothermic reactions tend to be spontaneous, while endothermic reactions tend not to occur without a source of energy Many of the reactions that occur in organisms are endothermic; animals obtain energy for endothermic reactions from metabolizing food, whereas plants capture sunlight (photosynthesis) and store some of the energy in GLUCOSE- C 6 H 12 O 6

7. A CATALYST is a substance that speeds up a reaction by lowering the activation energy; an ENZYME is a biological catalyst Ex. carbonic anhydrase speeds up CO 2 combining with H 2 O

9. Note that enzyme names end in –ase, with a root derived from the reaction it catalyzes Ex. lactase catalyzes the breakdown of lactose, a sugar

10. Enzymes 1. are very reaction-specific; a particular enzyme only catalyzes one particular reaction 2. are reusable; they are not changed in the reaction 3. are proteins, with a particular shape

11. The reactant(s) of an enzyme-catalyzed reaction is/are called the SUBSTRATE(S) Because an enzyme is a protein with a particular shape, it has a site on the molecule, called the ACTIVE SITE, into which the substrate(s) fit, forming the ENZYME-SUBSTRATE COMPLEX Often, the complimentary shapes of the active site and substrate(s) are compared to a lock and key; LOCK AND KEY model

13. Numerous factors can affect the activity of an enzyme 1. pH2. temperature3. amt. of substrate SEE “ANALYZING DATA, HOW DOES pH AFFECT AN ENZYME” P. 51 Cells typically regulate the activity of enzymes with other proteins that turn the enzyme “on” or “off” as needed by the cell