A subunit of DNA or RNA. To form a DNA or RNA molecule, thousands of nucleotides are joined in a long chain.
Each nucleotide is divided into three parts:
1. A nitrogenous base (A, G, T, or C in DNA; A, G, U, or C in RNA),
2. A phosphate molecule, and
3. A sugar molecule (deoxyribose in DNA and ribose in RNA).
A DNA oligonucleotide is a short piece of DNA composed of relatively few (oligo-) nucleotide bases.