Summary: A transfer RNA (tRNA) is is an adaptor molecule made out of RNA that serves as the physical link between the nucleotide sequence of nucleic acids (DNA and RNA) and the amino acid sequence of proteins. There are many tRNAs, most of which are specific for a particular amino acid. Each tRNA binds its amino acid and contains a three-nucleotide sequence called the anticodon, which forms three base pairs with a matching codon in mRNA during protein biosynthesis. The amino acid is covalently attached to the terminal phosphate group of a CCA motif present at the 3'-end of the tRNA. More specifically, the phosphate is attached to position 5 of the ribose of the terminal adenine ribonucleotide of the tRNA. This covalent attachment is catalyzed by dedicated aminoacyl-tRNA synthetases |CITS: |. The bound amino acid is then delivered to the ribosome by proteins called elongation factors (EF-Tu in bacteria, eEF-1 in eukaryotes). This class encompasses uncharged tRNA molecules. The structure shown indicates the phosphate group at the 3'-terminus, to which amino acids are attached.
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