Mutations

April 2010
Written by Stacey Herzer

The human body is an amazing wonder.  We are made up of building blocks called cells.  In each of our cells there is a genetic recipe book filled with instructions on how to make the right proteins at the right time to survive. This information is encoded in the DNA that makes up our genes. Just like good recipes call for certain ingredients to be added in the proper order to make a tasty dish, our DNA codes for amino acids that in the right order form functional proteins.    

We can think of DNA as a recipe that spells out our ingredients, and the ingredients are amino acids that come together to give us our final product.
   
To make coffee we need:

  • 1 cup hot water
  • 1 tablespoon ground coffee

When we mix the ground coffee and the hot water we get a nice cup of coffee.

A mutation is a permanent change in the DNA sequence that makes up a gene. It can be as small as a single base change which is called a point mutation, it can involve the addition or deletion of a piece of a gene, or it can even involve multiple genes on a chromosome.

Types of mutations:

  1. Point mutants—single nucleotide base substitutions that result in three situations:
    • Missense mutations are point mutations that result in a single amino acid change within the protein. In this case, “coffee” becomes “toffee” and this changes our final product.
    • Nonsense mutations are point mutations that create a premature "translation stop signal" (or "stop" codon), causing the protein to be shortened.  In this case, instead of coffee we just get hot water; the coffee is eliminated because you stopped reading the recipe after adding hot water.  
    • Silent mutations are point mutations that change the nucleotide base, but because there are multiple combinations that still code for the same amino acid, there is no change in the amino acid sequence or the final protein. In this case we still get coffee; we don’t even notice the difference.
  2. Insertion mutants—these mutations add a little extra to the protein that isn’t supposed to be there. In this case it would be like doubling the amount of water used, and would give us a pretty weak cup of coffee, or it could be like doubling the amount of coffee used and would give too strong a cup of coffee.
  3. Deletion mutants—these mutations eliminate part or all of protein. In this case we would eliminate the coffee or the water or both, and we would not get a cup of coffee.  

For more information on how DNA information leads to proteins, please see the following:

For another explanation of mutations, see: http://learn.genetics.utah.edu/archive/mutations/