TRIS (tris(hydroxymethyl)aminomethane):
Firstly it's used to get the right pH for DNA extraction, but Tris is preffered over other buffers because Tris interacts with the lipopolysaccharides present on the outer membrane which helps to permeabilize the membrane. This effect is enhanced with the addition of EDTA (ethylenediaminetetraacetic acid), which is a chelating agent that captures metal ions (like Ca2+).