These bonds are called phosphodiester bonds, and the sugar-phosphate backbone is described as extending, or growing, in the 5' to 3' direction when the molecule is synthesized. In double-stranded ...

This step occurs by transesterification; in this case, an OH group at the 3′ end of the exon attacks the phosphodiester bond at the 3′ splice site. The adjoining exons are covalently bound ...