A polynucleotide molecule is a biopolymer composed of 13 or morem 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.Although DNA and RNA do not generally occur in the same polynucleotide, the four species of nucleotides may occur in any order in the chain. The sequence of DNA or RNA species for a given polynucleotide is the main factor determining its function in a living organism or a scientific experiment.