First the cells must be collected. If the cells are part of a hard surface or sample, they must be washed from the sample into a liquid solvent. If they are part of a soft tissue, then they are easier to isolate and remove. Once the cellular material is isolated, the cell membrane and associated proteins must be broken down to allow access to the DNA buried in the center of the cell. This is done with surfactants, or soaps. Commercial soap solutions are mixed with the cells to lyse (rupture) the membranes and denature (unfold) the proteins. Simple enzymes are then added to help break down any additional proteins that are associated with the DNA. But care must be taken not to make the enzymes too harsh or the DNA can be damaged, too. Finally, alcohol is added to the aqueous mixture. DNA is insoluble in ethanol, so it precipitates and can then be physically collected and removed from the medium for study. PCR (polymerase chain reaction) is often used to replicate and amplify the DNA to make it easier to study the specific sequences involved.