MOL - Mutations [LESSON]

Mutations

Mutations are changes in the natural error rate of nucleotide sequence during DNA replication.  During typical replication, DNA polymerase I proofreads and ensures that the mutation rate stays low. There are other types of DNA repair as well but these are beyond the scope of this course. However, despite all of the efforts to repair errors, there are still a LOT of mutations that are made and passed to daughter cells. Here are some of the most common.

Mutations at the DNA level are divided into two types: substitution changes one nucleotide and frameshift inserts or deletes a nucleotide.

Click through the Mutation slideshow below to learn more about each type.

 

 

The image shows the three types of substitution mutations listed below

There are three kinds of substitution mutations:

  • Silent mutations do not affect the sequence of amino acids during translation.
  • Nonsense mutations result in a stop codon where an amino acid should be, causing translation to stop prematurely.
  • Missense mutations change the amino acid specified by a codon.

The image shows the two types of frameshift mutations listed below

An insertion occurs when one or more bases are added to a DNA sequence. A deletion occurs when one or more bases are removed from a DNA sequence. Because the genetic code is read in codons (three bases at a time), inserting or deleting bases may change the "reading frame" of the sequence. These types of mutations are called frameshift mutations.

Now, watch the Mutation video below to understand more about how these mutations can affect phenotype.

Will a missense mutation (single amino acid change) affect the function of the protein?  It depends on multiple factors – here are some things to consider.

  • Is the mutation in the active or allosteric site? Or is it in a non-bonding region?
  • Is the amino acid’s size or polarity (charge) changing drastically?

In the Mutation Practice activity below click the answer button and then the next arrow to move on.

Now, practice inserting a mutation into the DNA strand below and then transcribing it.  What will happen to the protein?

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