Question

What are the three stages of translation? Discuss the main events that occur during these three stages.

Short answer

The three stages of translation are: Initiation (where the ribosome subunit binds to mRNA), Elongation (addition of amino acids to the polypeptide chain) and Termination (process stops when a stop codon is encountered and the polypeptide is released).

Step-by-step solution

Stage 1: Initiation

Initiation is the first phase of translation. In this process, the smaller ribosomal subunit binds to the mRNA. Then, the tRNA which carries methionine (Met) finds and binds to the start codon of the mRNA. After that, the larger ribosomal subunit binds and forms a complete initiation complex. This process sets up the site for protein synthesis.

Stage 2: Elongation

Elongation is the second phase where the amino acids are added to the growing polypeptide chain. A tRNA molecule that matches the next codon enters the ribosome and binds to the codon. This tRNA molecule brings in a new amino acid to add to the string of amino acids. The ribosome moves one codon further along the mRNA, and the above processes continue with the next tRNA molecule.

Stage 3: Termination

During the termination phase, the translation stops when the ribosome reaches a stop codon on the mRNA. It does not code for any amino acids, hence no tRNA molecule can bind to it. As a result, the process of protein synthesis stops and the newly formed polypeptide is released.