A polynucleotide molecule is a biopolymer composed of 13 or more nucleotide monomers covalently bonded in a chain. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are examples of polynucleotides with distinct biological function. The prefix poly comes from the ancient Greek πολυς (polys, many). DNA consists of two chains of polynucleotides, with each chain in the form of a helical spiral.