When a termination codon enters the A site, translation halts. This is because there is no tRNA with an anticodon that is complementary to any of the stop codons. |
Instead, the termination codon is recognized and bound to by a release factor. The release factor is a protein, like the initiation factors and the elongation facotrs, that is independent of the ribosome. |
The release factor causes the translation complex to fall apart, and cleaves the polypeptide from the final tRNA. The polypeptide product is now free to function in the cell. The mRNA molecule is now available to be translated again. Very often, more than one ribosome will translate a single mRNA at the same time. One ribosome will initiate translation, and after it moves down the mRNA a bit, another ribosome will initiate, then another, and so on. The structure consisting of multiple ribosomes translating a single mRNA molecule is called a polysome. Eventually, the mRNA is degraded, and translation of that particular message will cease. |