8.5: Translation-Protein Synthesis
- Define and understand the mechanism of biological translation.
Translation in biology is the process of protein synthesis using the information encoded in mRNA.
Translation process
The process starts when the ribosome binds to mRNA in the cytoplasm, as illustrated in Figure \(\PageIndex{1}\). The ribosome moves along the mRNA from 5' to 3" direction until it reaches the stats codon AUG. The AUG is also the codon for methionine. So, the methionine-tRNA (methionine-loaded aminoacyl-tRNA) with the complementary anticodon UAC arrives and aligns opposite the codon AUG. The aminoacyl-tRNA with a complementary anticodon to the codon next to AUG on the mRNA arrives and aligns opposite the codon.
Ribosome catalyzes a peptide bond formation between \(\ce{-NH2}\) group of the amino acid on the second tRNA with the carboxylate group of the first by nucleophilic acyl substitution mechanism. The first tRNA becomes empty, and the second tRNA becomes peptidyl-tRNA. The ribosome moves on to the next codon -a process called translocation . The empty-tRNA leaves and a new aminoacyl-tRNA with a complementary anticodon to the third codon align on the mRNA and repeat the above process, as illustrated in Figure \(\PageIndex{2}\). The cycle repeats, and the peptide keeps elongating until the ribosome reaches a stop codon. The translation process stops at this point, and the newly formed peptide is released. The first methionine is usually removed from the peptide. The empty tRNA are re-loaded with the amino acid later on, as illustrated in Fig. 8.4.2. The hydrogen bonding and the other intramolecular interaction, like salt bridges, disulfide bonds, etc., make peptides acquire the secondary, tertiary, and sometimes quaternary structure. This is how functional proteins with the appropriate forms are synthesized.
Figure \(\PageIndex{3}\) presents a simulation that summarizes the process of transcription and translation and the trinucleotide codons in DNA, mRNA, anticodons on tRNA, and the corresponding amino acids in the polypeptide that are shown in the simulation. Watch the DNA and RNA video summary by clicking this link or the video below.
Antibiotics that interrupt protein synthesis in bacteria but not in humans are clinically useful. Some examples and their actions are shown in Table 1.
| Antibiotic | Effect on protein synthesis in bacteria |
|---|---|
| Tetracycline | Prevents the aminoacyl-tRNA from binding to the ribosome |
| Erythromycin | Prevent the translocation of the ribosome along the mRNA |
| Streptomycin | Inhibits the initiation of protein synthesis |
| Chloramphenicol | Prevents the new peptide bond from being formed |