Polynucleotide Directionality

Polynucleotides have directionality !

    Adjacent nucleotides in a single strand of DNA (polynucleotide) are joined by a phosphodiester bond between their 3' and 5' carbons. (Recall that an ester bond is R - O - R: the bond here is C - O - P - O - C). This means that the respective 5' and 3' carbons are exposed at either end of the polynucleotide, which are therefore called the  5' end and the 3' end. These are also called the phosphoryl and hydroxyl ends, respectively, because of the chemical groups typically found at those ends.

    A polynucleotide therefore has directionality: the two ends of the molecule have very different biochemical properties, and behave very differently in molecular genetic processes.  It is therefore critical to recognize which end is which.

A detailed understanding of this figure is critical to the first part of the course !!!

All text material © 2015 by Steven M. Carr