The genetic material in majority of organisms is DNA. For the restriction enzymes to cut DNA, it has to be in a pure form and free from other macromolecules. For this the cell needs to break open and release DNA with other macromolecules like RNA, proteins, polysaccharides and also lipids. This can be achieved by treating the cell with enzymes like lysozymes, cellulose, etc. The RNA is removed by ribonuclease and proteins by proteases. Similarly other macromolecules are removed by appropriate enzymes and finally DNA can be precipitated out as a collection of fine threads in the suspension after adding chilled ethanol.