I am currently studying DNA extraction from various bio-originated samples. I am new to this field, and have learned how commercial DNA extraction kits work for bacteria.
I understand that the very first step is called 'lysis', and that this is supposed to break cells to pull out all the stuff inside them, including DNA.
I am studying cell-free DNA extraction procedure from human blood, and I don't understand why the lysis step is necessary in this context.
If lysis is to break cells, and cell-free DNA is already out of the cell and freely circulating, such a step seems unnecessary.
Is my understanding about lysis right? Then, why is the lysis step necessary during cfDNA isolation?