Question

How does translation termination occur?

Short answer

Answer: The main components involved in translation termination are the ribosome, mRNA molecule, stop codons, release factors, tRNA molecules, and newly synthesized polypeptide chain. The key steps are the ribosome encountering a stop codon (UAA, UAG, or UGA) on mRNA, release factors recognizing the stop codon and facilitating the release of the polypeptide chain, and the dissociation of the ribosome into its subunits for another round of translation.

Step-by-step solution

1. Components of Translation Termination

Translation termination occurs when a ribosome reaches the end of a coding sequence on a messenger RNA (mRNA) molecule. The main components involved in the process are the ribosome, mRNA molecule, stop codons, release factors, tRNA molecules, and newly synthesized polypeptide chain.

2. Stop Codons

Stop codons are special nucleotide triplets in the mRNA sequence that do not code for any amino acids. They signal the ribosome that the translation process should end. There are three stop codons: UAA, UAG, and UGA.

3. Interaction between Ribosome and Stop Codon

As the ribosome moves along the mRNA and reads the nucleotide sequence in triplets (codons), it eventually encounters a stop codon. The ribosomal A site encounters one of the three stop codons, and instead of using aminoacylated tRNA to insert the next amino acid, the ribosome recognizes it as a termination signal.

4. Release Factors and Termination of Translation

When a stop codon arrives at the ribosomal A site, translation is terminated by the action of proteins called release factors (RFs). In prokaryotes, two release factors are involved: RF1 and RF2, while in eukaryotes, there is only one release factor called eRF1. These release factors recognize the stop codons and facilitate the hydrolysis of the bond between the new polypeptide chain and its tRNA, which is in the ribosomal P site. This process releases the newly synthesized polypeptide from the ribosome.

5. Ribosome Dissociation

After the release of the new polypeptide chain, the ribosome dissociates into its two subunits, which can be later assembled for another round of translation. The mRNA molecule is also released from the ribosome complex, and the process is completed. The polypeptide chain then undergoes further folding and modification before it becomes an active protein.