|MadSci Network: Biochemistry|
Hello, Cecilia - sorry that this answer is so late. When you added H2O2 (Hydrogen Peroxide) to the piece of liver, the catalase reacted with the H2O2 and O2 (Oxygen) gas was formed, as you noticed. However, the reaction involved catalase as a catalyst . You should probably think of enzymes in general as being catalysts -- the definition of a catalyst is: "a substance that causes or speeds a chemical reaction without itself being affected" The catalase itself was not used up -- it simply helped the hydrogen peroxide break down into water by the reaction: H2O2 ---> H2O + 1/2 O2 or 2H2O2 --> 2 H2O + O2 Perhaps it will help if you can imagine that a catalyst is like a tool, perhaps a pair of scissors you use to cut paper. The "reaction" is taking sheets of paper and converting them to different shapes. You and your scissors make this "reaction" happen, but neither you nor the scissors are "used up" in the reaction. An enzyme is a catalyst made up of amino acids -- so, it's a special type of protein that forms into a shape such that reactants such as hydrogen peroxide readily attach to it, and once all the reactants are in place next to the enzyme, the chemical reaction takes place among the reactants attached to the enzyme, and then the products of the reaction generally move off. So, in the case of catalase, that particular enzyme attaches to one reactant, hydrogen peroxide, and then helps the hydrogen peroxide to break apart into water and oxygen molecules. The catalase itself stays intact. In your experiment, the catalase was able to break down the hydrogen peroxide the second time you tried it because the catalase had NOT been broken down the first time. As for when the catalase would break down -- well, biochemicals like proteins (and enzymes are proteins that have the function of being catalysts for chemical reactions) can have a varied lifetime depending on the environment. If they are kept at a high temperature, they may breakdown or just change their shape ("denature") and become useless fairly quickly. On the other hand, if you store it in a cool location and have it only be in contact with something fairly inert, like nitrogen gas, then the enzyme could last for many years. I hope this helps!
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