a tRNA with a 3' CC end + ATP <=> a tRNA with a 3' CCA end + diphosphate
a trna with a 3' cc end + atp <=> a trna with a 3' cca end + diphosphate
a tRNA with a 3' CC end + ATP <=> a tRNA with a 3' CCA end + diphosphate
a trna with a 3' cc end + atp <=> a trna with a 3' cca end + diphosphate