In the first step, the 2'-OH of an adenosine in the intron (the branch site A) attacks the phosphodiester bond at the 5' splice site to release the upstream exon and form a branched or lariat ...
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 ...