2.  Proteins are composed of smaller units called amino acids.  Amino Acids : Are small compounds that are made of carbon, nitrogen, oxygen, and hydrogen.

3.  Activation Energy : The minimum amount of energy needed for reactants to form products in a chemical reactions.

4. A catalyst, as well as an enzyme, is a substance that lowers the activation energy needed to start a chemical reaction. * Catalysts speeds up chemical reactions thousands of times faster.

5. Enzymes are biological catalysts that speed up the rate of chemical reactions. * Enzymes are made of proteins. Example: Amylase found in saliva. Amylase speeds up the breakdown of amylose, a substance in starch (in foods). * Most enzymes are specific to 1 reaction

6. Substrate : The reactants that bind to the enzyme. Active Site : The specific location where a substance binds to an enzyme. * The active site and the substrate have complementary shapes (“Lock & Key”) Click on picture to see an animation!

7. Only substrates with the same size and shape as the active site will bind to the enzyme (like puzzle pieces). pH and temperature mainly affect enzyme activity. Click on picture for link

8.  Pepsin is an enzyme in the stomach that begins the digestion of proteins by splitting them into smaller pieces.  Pepsin works at a pH level of around 2 which is acidic  Antacids are used to neutralize pepsin by increasing the pH level to around 6 or 7