Short answer: There can be 60 different tRNAs in a cell or organelle, including isoacceptors for a single codon. However, all of these tRNAs must bind a single species of each protein synthesis factor (in bacteria, IF2 for initiation and EFTu for elongation), and every tRNA must interact in the same way with the ribosome. As it turns out, the CCA sequence is one "common feature" shared by all tRNAs. For example, the CCA sequence makes specific H-bond interactions with rRNA sequence in or around the peptidyl transferase center. (I don't have specific information handy for interaction of the CCA with translation factors or aminoacyl tRNA synthetases, but this should get you started.)
Basically tRNA acts as a physical link between nucleic acids and amino acids. It carrying amino acids to protein synthesizing machinery ribosomes. The CCA3' sequence in the amino acid arm is very important for the recognition of specific tRNA with its enzyme (aminoacyl-tRNA synthetase). It is also required to carry a specific amino acid esterified by its COO group to the 2' OH-group of adenine of CCA3'.
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