DNA polynucleotide chain growth

During DNA synthesis, new nucleotides are added to the existing 3' end by a 3'  5' phosphodiester bond (R - O - P - O - R).  The original 5' end remains unmodified.  Polynucleotides thus "grow" by modification of the 3' end, in the 5'3' direction. Nucleic acid biochemical processes occur only in the 5'3' direction.


Figure after © 1997 Klug & Cummings; All text © 2011 by Steven M. Carr