5. Puromycin is an antibiotic that has an effect on both prokaryotes and eukaryotes. Puromycin, which is structurally similar to the aminoacyl terminus of an aminoacyl-tRNA (see diagram), inhibits protein synthesis by releasing nascent polypeptide chains before their synthesis is completed. Explain how puromycin can affect this result on growing polypeptide chains and why the peptide chain is released. (4 分)