What is the nucleophile in each of the following reactions? For each reaction, precisely indicate not just the atom or g

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What is the nucleophile in each of the following reactions? For
each reaction, precisely indicate not just the atom or group that
is involved but also the larger context. Example: the nucleophile
in the synthetic reaction catalyzed by E. coli DNA polymerase I is
the oxygen atom of the 3’-OH group on the 3’ nucleotide of the
newly synthesized DNA strand
(a) In aminoacyl-tRNA, migration of the covalently attached
amino acid from the 2' position of A76 to the 3' position of A76.
[A76 is the 3'-terminal nucleotide at the end of the tRNA]
(b)Activation of the 5'-phosphate at a nicked site, in the
mechanism of DNA ligase
biochem question