5' to 3' Direction

∞ generated and posted on 2015.12.27 ∞

Order of addition of nucleotides during nucleic acid polymerization.

5' to 3' Direction refers to the carbon numbers of the sugars ribose and deoxyribose which contain hydroxyl groups to which incoming nucleotides are attached during polymerization, with addition specifically to the 3' hydroxyl group, resulting in increases in length at the 3' end, hence polymerization in the 5' to 3' direction.

The primes (') refer to carbons associated with the sugars ribose or deoxyribose (the nitrogenous bases, by contrast, are numbered without the primes). See similarly 5' to 3' polarity.

The 3' hydroxyl group found on these sugars is the target for nucleotide addition, as recognized by both DNA polymerase enzymes and, less stringently, by RNA polymerase enzymes as well. RNA priming in fact specifically supplies a 3' hydroxyl group in its job of initiating the synthesis of DNA daughter strands.

The 3' carbon in polynucleic acids is linked to a phosphate group as one side of a phosphodiester linkage. The 5' carbon, on the other hand, is linked to the other side of the phosphodiester linkage. The backbone of nucleic acid polymers therefore can be described as consisting of:

Phosphate group5' carbon4' carbon3' carbonphosphate group5' carbon, etc.