iGen3 02-09b smc

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.

Figure © 2010 PJ Russell, iGenetics 3rd ed.; all text material © 2011 by Steven M. Carr