DNA and RNA are chemically very similar. The primary structures of both are liner
polymers composed of monomers callednucleotides. DNA and messenger RNA
function primarily as informational molecule, carrying information in the exact sequence
of their nucleotides. Cellular RNAs range in length from about 22 to many thousands of
nucleotides. Cellular DNA molecules can be as long as several hundred million nucleotides.
These large DNA units in association with proteins can be stained with dyes and
visuallized in the light microscope as chromosomes, so named because of their
stainability.