How do mutations change proteins?

We’ve talked about mutations and how they can be good, bad or neutral, but how does that work exactly?  This is the nitty gritty. Remember back to how DNA is transcribed into messenger RNA which is then translated into the protein?  This is based on a three letter code – where each 3 letters of the RNA makes on amino acid. (If you’re interested in knowing how 4 nucleotides, which have 64 possible combinations makes only 20 amino acids, see my Answers page). If you change one of these amino acids a number of things can happen.

To make it easier, let’s pretend that these codons make the sentence “DNA HAS ALL YOU CAN ASK FOR” (see the picture below).  You may change one letter and it doesn’t change the meaning of the sentence (or the function of the protein) at all, making it a “silent” mutation. You may change one letter and it does change the meaning, but maybe not significantly – this is a missense mutation.  You may have a mutation that stops the sentence early – this would make a protein that is shorter than it’s supposed to be and probably will cause the protein to function improperly.  This is a nonsense mutation. Finally, you may add or remove one or many nucleotides which shifts the letter of the sentence so that they no longer make any sense.  These frameshift mutations also will affect the protein, and likely not in a good way.

protein_mutationsNow you can see how small changes may or may not affect the protein.    It’s interesting because it helps really explain how ONE nucleotide change can affect a protein and cause disease.  Also, if you think about the effect one nucelotide change can have, it helps us understand how finding and understanding these changes can be important for diagnosing disease.


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