5 end of polynucleotide chain phosphate 9.2 Transcription being added to chain is catalyzed by RNA polymerase O=P Figure 9.6 Phosphodiester bond formation involves a hydrophilic attack by the 0=P.O 3-OH group of the last nucleotide of the chain on OsP.O O=P·O the 5 triphosphate of the Pyrophosphate incoming nucleotide. with release of pyrophosphate 消当Figure 9.6 Phosphodiester bond formation involves a hydrophilic attack by the 3’-OH group of the last nucleotide of the chain on the 5’ triphosphate of the incoming nucleotide, with release of pyrophosphate. 9.2 Transcription is catalyzed by RNA polymerase