2.4 Chemical Reactions and Enzymes

2 Chemical Reactions A process that changes or transforms one set of chemicals into another Mass and energy are conserved Reactants  Products 2 kinds: energy releasing (exothermic) and energy absorbing (endothermic)

Exothermic Reactions Reaction in which heat is given off (Ex. combustion of fuels) 3

Endothermic Reactions Reaction in which heat is absorbed (Ex. water is evaporated) 4

Activation Energy Energy needed to get a reaction going 5

Catalyst A substance that speeds up the rate of a reaction It works by lowering activation energy 6

Enzymes Proteins that act as biological catalysts They speed up chemical reactions that take place in cells They are very specific and usually catalyze only one chemical reaction 7

Substrates The reactants of enzyme-catalyzed reactions They bind to sites on the enzyme called active sites  Lock and Key CO 2 + H 2 O  H 2 CO 3 substrate 8

Regulation of Enzyme Activity Temperature, pH, and regulatory molecules can affect how well enzymes work Pepsin works best under acidic conditions (begins protein digestion) Some are regulated by molecules that carry chemical signals within cells that turn enzymes “on” or “off” 9