Enzymes are organic molecular proteins composed of amino acids. At any point in time, when work is taking place within a cell, it is being accomplished by the enzymes. Their purpose is to facilitate swift chemical reactions that allow the cell to break things down or assemble things as necessary. These processes are what allow a cell to grow and reproduce.
When enzymes are formed, somewhere between 100 and 1,000 amino acids string together in a unique and specific order. This chain then takes on a unique shape which permits the enzyme to host particular chemical reactions. Each enzyme serves as a highly efficient catalyst for that specific reaction.
One example involves maltose. This sugar is made when a pair of glucose molecules bond together. The related enzyme, maltase, has a specific shape that allows it to undo the bond, freeing the two pieces of glucose. While the only purpose of maltase is to break up maltose molecules, maltase enables cells to do this efficiently and quickly. Other enzymes have other functions that they facilitate, but one thing that they have in common is that they either assemble molecules or break them into pieces, and there are specific enzymes for all of the chemical reactions that cells need to function properly.