2.4 Chemical Reactions and Enzymes

1. 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)

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

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

5. Activation Energy • Energy needed to get a reaction going

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

7. 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

8. Substrates • The reactants of enzyme-catalyzed reactions • They bind to sites on the enzyme called active sites Lock and Key • CO2 + H2O  H2CO3 substrate http://www.youtube.com/watch?v=CZD5xsOKres

9. 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”