DNA nucleotides. Note that adenine, thymine, cytosine and guanine are NOT nucleotides, but they are only the bases which make the nucleotides different.
we haven't found all of them yet so I can't tell you, most likely in the tens of billionsThe answer above is correct if your talking about how many nucleotides are contained in DNA. But they all...
Adenine, guanine, cytosine and thymine. Adenine and guanine are double ringed purines and cytosine and thymine are pyrimidines of a single carbon/nitrogen ring.