Almost all enzymes are proteins, but there are a few exceptions. In ribonucleoprotein enzymes, the enzyme activity happens in the RNA instead of the protein, according to Dr. John W. Kimball.
Enzymes reduce the amount of energy needed to complete a chemical reaction. Each enzyme participates in specific reactions by binding with the reacting molecules at its active site. Enzyme activity is affected by temperature, pH level and other factors. If the protein part of the enzyme changes shape, the enzyme may not be able to work as intended, an effect called denaturation. In humans, enzymes regulate all of the chemical reactions necessary for survival.