Why is ribonuclease often included in lysis buffer when extracting dna? What is its function?
This is an enzyme which will break down RNA, which helps to produce a lysate with DNA without RNA impurities.
Ribonuclease is an enzyme, the "ase" ending is a dead give-away that you are dealing with an enzyme.
The enzyme breaks down RNA (RNA = ribonucleic acid).
The goal of extraction is to purify the DNA as much as possible. Because the lysate (contents of a broken open cell) will have both DNA and RNA, the ribonuclease helps to remove the unwanted RNA.
Hope this helps!