DNA polynucleotide chain
The two ends of the polynucleotide chain have
different chemical properties, and are designated the 5' end
[shown at right] and the 3' end [shown at left],
respectively, according to the reactive deoxyribose carbon
at either end. The 5'
end is also called the phosphoryl end, because a
single PO4 group
is usually attached to it. Likewise, the 3' end is also called
the hydroxyl end, becaue of the -OH group attached to
the 3' carbon.
Note that designation of the ends as "right" or "left" is arbitrary: do not assume that DNA strands will always be drawn from left to right in the 5' to 3' or PO4 to OH directions.
Note that designation of the ends as "right" or "left" is arbitrary: do not assume that DNA strands will always be drawn from left to right in the 5' to 3' or PO4 to OH directions.