DNA is simply a code maintained by the order of the nucleotides. The DNA is the sequence, but like any code, it requires something to decode it or read it. This is where messenger and transfer RNA come into play and the process of protein synthesis occurs.
DNA is ideal because it can be condensed into tiny packages, or chromosomes and fit into the nucleus of every cell. Other material would be much to large to be contained, in such detail, in each cell.
yes this could be because it shows what changes have altered the basic compounds of the DNA samples