Here's why:

* Cell membrane: This outer layer of the cell encloses all the cellular components, including the nucleus where the DNA is located.

* Nuclear envelope: This membrane surrounds the nucleus and protects the DNA.

Breaking down these membranes allows you to access the DNA within the nucleus. This is typically achieved using:

* Detergents: These chemicals disrupt the lipid bilayer structure of the membranes.

* Enzymes: Specific enzymes like lysozyme can break down the cell wall (in plant cells) and the cell membrane.

Once the membranes are broken down, the DNA is released into the solution, where it can be further purified and isolated.