Dna double helix is composed of two strands of dna; each strand is a polymer of dna nucleotides. each nucleotide consists of a sugar, a phosphate group, and one of four nitrogenous bases. the structure and orientation of the two strands are important to understanding dna replication. drag the

The DNA double helix is constructed from two strands of DNA, each with a sugar-phosphate backbone and nitrogenous bases that form hydrogen bonds, holding the two strands together. Each DNA strand has two unique ends. The 3' end has a hydroxyl (-OH) group on the deoxyribose sugar, whereas the 5' end has a phosphate group. In the double helix, the two strands are antiparallel, that is, they run in opposite directions such that the 3' end of one strand is adjacent to the 5' end of the other strand.