DNA vs. RNA

What's the difference between DNA and RNA?

Both DNA and RNA are composed of repeating units of nucleotides. Each
nucleotide consists of a sugar, a phosphate and a nucleic acid base.
The sugar in DNA is deoxyribose. The sugar in RNA is ribose, the same
as deoxyribose but with one more OH (oxygen-hydrogen atom combination
called a hydroxyl). This is the biggest difference between DNA and RNA.
Another difference is that RNA molecules can have a much greater variety
of nucleic acid bases. DNA has mostly just 4 different bases with a few
extra occasionally.  The difference in these bases (between DNA and RNA)
allows RNA molecules to assume a wide variety of shapes and also  many
different functions. DNA, on the other hand, serves as a set of directions
and that's about all (but that's absolutely necessary!). ---DrPam

http://www.newton.dep.anl.gov/askasci/bio99/bio99410.htm