What indicates the end of a coding sequence in mRNA where the ribosome should stop adding amino acids?

The end of a coding sequence in mRNA where the ribosome stops adding amino acids is indicated by specific sequences called stop codons. These stop codons are located at the 3′ end of the coding region, signaling the ribosome to terminate translation and release the newly synthesized polypeptide chain. The 5′ end and the 5′ cap are important for mRNA stability and translation initiation, but they do not play a role in indicating the end of protein coding.

The poly-A tail is not directly involved in signaling the end of the coding sequence; rather, it contributes to the stability of the mRNA molecule and affects its translation efficiency and export from the nucleus. The distinction between the functioning parts of the mRNA is crucial in understanding how protein synthesis is regulated and executed within the cell.