Is DNA usually a string of nucleotides

In living organisms DNA does not usually exist as a single molecule, but ... Levene suggested that DNA consisted of a string of nucleotide units

DNA is made up of three subunits: a deoxyribose 5 carbon sugar, a phosphorous group, and a nitrogenous base (adenine, thymine, guanine, cytosine). All in all, these are called nucleotides that wrap around in a double helix in order to form DNA.