What is the significance of an -OH group on the 3' end of DNA?

The presence of an -OH group on the 3' end of DNA is crucial because it is essential for the elongation of the DNA strand during DNA synthesis. The -OH group serves as a reactive site where nucleotides can be added to the growing DNA chain through phosphodiester bonds. In DNA polymerization, the enzyme DNA polymerase reacts with this -OH group to form covalent bonds with the phosphate group of incoming nucleotides, facilitating the continuation of the DNA strand. This reaction cannot occur at a 3' end without an -OH group; hence, the ability to add new nucleotides and elongate the DNA strand is directly dependent on this functional group. Without the -OH at the 3' end, DNA synthesis would halt, as there would be no site for the attachment of additional nucleotides. Therefore, the -OH group on the 3' end plays an integral role in the process of DNA replication by enabling the elongation of the DNA strand.