DNA is made up of three units.
1. Phosphate group
2. Deoxyribose sugar
3. Nucleotide or Nitrogenous Base
There are four different bases found in DNA.
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
They bind very specifically; so A only binds to T and G only binds to C
Links
Base pairing
Biochem site
Genome talking glossary
Genetics home reference
Extension
National Centre for Biotechnology Educatioan