As it relates to restriction enzymes...
In prokaryotes, restriction enzymes cut up foreign DNA to protect the cell from inadvertantly copying outside DNA (i.e., from a phage). The cell protects its own DNA by methylation. Methyl groups are added to the 6N of A and the 5C of C in its own DNA.
Why are the methyl groups added only to A and C? What about the chemical structure of A and C makes them receptive to methyl groups, and what about T and G makes them unreceptive?
I'm still in highschool and just learning the beginnings of biochemistry, so please feel free to dumb things down. I am atleast familiar with functional groups and have a basic knowledge of Lewis dot structures, which I'd guess is vital to understanding this phenomena.
Anything to shed some light on this question would be appreciated.