mechanisms 883.mech.0221 Louis J. Sheehan, Esquire

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2. Prevention of translation of damaged mRNAs

MRNA can either (i) be incorrectly processed in the nucleus or (ii) be damaged in the cytosol. Because correct translation is critical, cells have several proofreading/correction mechanisms.

First, the recognition process looks for both the poly-a tail and the 5’cap (the absence of either is a clue that the mRNA is broken).

Second, cells have a “nonsense-mediated mRNA decay” system. This system allows the cell to assess that a given mRNA molecule has a stop (nonsense) codon (UAA, UAG, or UGA) in the wrong location; this mislocation can occur when an mRNA molecule is spliced incorrectly. The “nonsense-mediated mRNA decay” system expects to see the proper stop codon located within the last exon; if this is not the case, the mRNA molecule is destroyed. The net result of this system means that cells only produce proteins (a.k.a. “full-length proteins”). This system is a God-send for people who have one functional gene and one mutant gene as this systems sees to it that only functional proteins are produced.