A polymer is a large molecule consisting of repeating structural units. In the case of nucleic acids, there are two polymers--DNA and RNA. DNA molecules consist of subunits called nucleotides. Each nucleotide in turn, contains a phosphate group, a sugar called deoxyribose and one of four nitrogenous bases--adenine, guanine, cytosine and thymine. DNA is double stranded and the bases are connected by hydrogen bonds. Adenine pairs to thymine and cytosine to guanine. DNA can contain millions of base pairs along its length, thus, it is a polymer. RNA, another nucleic acid is a single stranded molecule. It contains a different sugar called ribose and the same bases as in DNA-- adenine, guanine, cytosine, however, the base thymine is not present in RNA, instead, RNA contains a different base known as uracil. RNA is able to copy the DNA code and is also a large molecule known as a polymer.