Base complementarity and DNA structure Nucleic acid consists of nucleotides connected in a long, linear chain. The car- bons at the 3´ position and the 5´ position of each pentose link to a phosphate, forming a bridge between individual nucleotides. This is called a polynucleotide. NH 2 N - - N A N O H H H O H O HN O O H H P P P 5´ end CH 3 5´ 4´ 3´ A 1´ 2´ Looks kind of like a comb! O - O O - O N O P O P O P O CH 2 O O H 5´ end (since it's the end of the 5´ side) 5´ T N NH 2 P 5´ 5´ 4´ 3´ T 1´ 2´ or U - O P O CH 2 O H H