Investigation 34 Enzymes
Introduction One of the distinguishing features of living organisms is the presence of organic catalysts called enzymes. Those enzymes isolated to date have been found to be proteins; most are soluble in water or a dilute salt solution. However, enzymes found in mitochondria are bound together by lipoprotein (a phospholipid-protein complex) and this makes them insoluble in water. Some enzymes consist solely of protein. Others consist of two parts, one of which is a protein, an apoenzyme, the other being made of a smaller organic molecule, a coenzyme. In some cases the second portion is a metallic ion and is known as a cofactor. Separately, the apoenzyme and the coenzyme or cofactor remain inactive, but combined they form an active functional unit known as a holoenzyme.
Purpose To compare the action of catalase to a non-protein catalyst under different conditions.
Materials Materials Equipment
and 3% hydrogen peroxide fine clean sand
Equipment manganese dioxide stirring rod
fresh or frozen liver Bunsen burner or hotplate
potato 250 mL beaker
ice test tubes
Procedure Catalytic reactions
Add 2 mL of hydrogen peroxide to two test tubes. Place 0.1 g of sand in one test tube and add 0.1 g of manganese dioxide to the second tube. Observe and record the rates of reaction. What gas evolves?
B. The effect of an enzyme
Add 2 mL of hydrogen peroxide to each of two clean test tubes. In one place a small piece of liver and in the other a small piece of potato. Record the rates of reaction and compare these results to those with manganese dioxide. Do not discard these materials.
C. Re-using an enzyme
Divide the liquid portion of the previous tube in B containing the liver into two test tubes. Cut the liver from procedure B into two equal portions and add these to the two test tubes. To the first add a fresh piece of liver and to the second add 1 mL of hydrogen peroxide. Record your observations and...