Practice question

CCA synthesis by tRNA nucleotidyltransferase occurs without nucleic acid template, termed template-independent polymerization. Specificity arises from protein-side templating: active site pockets formed by amino acid side chains and backbone hydrogen bonds discriminate CTP versus ATP, with conformational remodeling after each addition switching nucleotide preference from CTP to ATP after two incorporations. Thus enzyme itself encodes CCA sequence. This mechanism allows universal addition to all tRNAs regardless of gene sequence and enables repair of cleaved or degraded tRNA ends in quality control.