We have that the DNA molecule is a double-stranded of complementary polymers of nucleotides that stores our genetic information to produce proteins and regulate their expression. These nucleotides of nucleic acids are composed at the time by a carbon ring of five atoms, known as pentose, also by the nitrogenous bases, by a phosphate group, and an OH functional group.
Those carbon atoms of the rings have also a particular orientation, and are numerated from 1 to 5, being in the 5' position, the phosphate group, while in the 3' position, the OH group; both complementing each other.