Describe the process of translation, explaining the role of tRNA in assembling the new polypeptide chains.
The process of assembling the amino acids based on the information supplied by the mRNA is called translation. As a ribosome moves along a strand of mRNA, it reads three nucleotides at a time, the length of a single coding unit, or codon, for a single amino acid. Of the 64 codons, 61 code for amino acids (most amino acids have several different but synonymous codes) and three that signal the beginning or end of a gene's sequence. But proteins are not synthesized directly from mRNA. Instead, amino acids are assembled in their proper sequence by the third type of RNA, transfer RNA (tRNA). Free-floating amino acids, after being activated by ATP, are joined to tRNA by enzymes and brought into the ribosome where they are linked together to form polypeptide chains. Each amino acid has at least one specific type of enzyme to bind it to tRNA and at least one specific type of tRNA to carry it to a ribosome. Each tRNA has an unpaired triplet of nucleotide bases, called an anticodon. During the time when the tRNA's amino acid is being linked to the growing polypeptide chain, the tRNA's anticodon forms a temporary bond with the corresponding, complimentary codon of the mRNA. Once free of its amino acid, the tRNA leaves the ribosome to pick up another amino acid and begin the assembly cycle over again.
