The side groups are what make each amino acid different from the others. Of the 20 side groups used to make proteins, there are two main groups: polar and non-polar. These names refer to the way the side groups, sometimes called "R" groups, interact with the environment.
It is a Chemical reaction taking place un a solution in which one or more of the products is insoluble in the solvent, and so forms solid particles that fall to the bottom of the reactor
