Question

What happens when a stop codon is reached by a ribosome?

A termination tRNA^ter binds to the codon and the growing peptide is transferred to it. When the peptidyl-tRNA^terreaches the P site, the ribosome is signaled to release the protein. The ribosome then is likely to dissociate.

A release factor binds to the codon and is used to release the growing peptide from the P site tRNA.

A termination tRNA^ter binds to the codon and the growing peptide is transferred to it. When the peptidyl-tRNA^terreaches the P site, the ribosome dissociates. A separate peptidyl transferase then releases the protein from tRNA^ter.

A release factor binds to the codon and the ribosome dissociates. A separate peptidyl transferase then releases the protein from the last tRNA to which was attached.

A termination tRNA^ter binds to the codon and is used to release the growing peptide from the P site tRNA. The ribosome then is likely to dissociate.

Answer 1

There are three stop codons: UAA, UAG and UGA. When a ribosome reaches any of these stop codons, the translation of proteins is terminated. A release factor binds to the stop codon that reaches the A-site on the ribosome. This process alters the activity of the peptidyl transferase in the ribosome, causing it to catalyze the addition of a water instead of an amino acid to the peptidyl tRNA. The carboxyl end of the polypeptide chain is freed from its attachment to a tRNA molecule, and the completed protein chain is immediately released into the cytosol.
Then, the ribosome releases the mRNA and dissociates into its two separate subunits, which can then assemble on another mRNA molecule to begin a new round of protein synthesis. So, the answer for this question is option 2.