by digesting various components of cell using enzymes
WE need only the DNA and not other parts like membranes and organelles.To remove other parts we use
enzyme to remove
cellulase plant cell
chitinase fungal cell wall
lysosyme bacterial cell
and many more and finally obtain the DNA
Because it degrades the cell membrane and all the other membranes inside the cell. The nucleus membrane is lipoproteic just like the plasmatic membrane. To get access to the genetic material the nucleus has to be broken first.