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. Do not talk
or think about the process any other way.
Figure after ©
1997 Klug & Cummings; All text © 2024
by Steven M. Carr