Mutate a Gene

A mutation is a permanent change in a DNA sequence. Some mutations can affect the protein a gene codes for.

The short DNA sequence below comes from the middle of a much longer gene. Change the DNA letters and see how it affects the resulting mRNA and protein. How do I edit the gene?

How do I edit the gene?

1. Point mutation (change one DNA letter)
   1. Select a base
   2. In the menu that pops up, choose the letter you want to change it to
2. Deletion mutation
   1. Select a base
   2. In the menu that pops up, choose the trashcan icon (see left image)
3. Insertion mutation
   1. Select an arrow (between bases)
   2. In the menu that pops up, choose which base you want to add (see right image)

What are the colors on the amino acids showing?

Cells read a gene’s DNA code as a series of three-letter “words” called codons. Each codon codes for a specific amino acid. Genes also have a reading frame. Take this DNA sequence as an example:

You could divide it into codons in 3 ways, each with a different reading frame:

1. GCA TGC TGC GAA ACT TTG GCT GA
2. G CAT GCT GCG AAA CTT TGG CTG A
3. GC ATG CTG CGA AAC TTT GGC TGA

Only one of these reading frames will code for a working protein. How can you tell which is the right one? It’s a little like finding the right spacing for the letters in a sentence. For example:

Only one reading frame makes a sentence that follows the rules of the English language: The sun was hot but the old man did not get his hat.

There are rules for reading genes too. For example, all protein-coding sequences begin with the codon “ATG” (AUG in mRNA). The correct reading frame will contain this codon.

Why isn't the start codon in DNA complementary to AUG?

Mutation is a process that causes a permanent change in a DNA sequence. Changes to a gene’s DNA sequence, called mutations, can change the amino acid sequence of the protein it codes for—but they don’t always.

Point Mutations
A point mutation is a change to single DNA letter. They fall into three categories:

• Missense mutations cause a single amino acid change in the protein.
• Nonsense mutations make a premature "stop" codon. Any codons after that are not translated, and the resulting protein is missing amino acids.
• Silent mutations code for the same amino acid as before.

Insertion and Deletion Mutations
Insertion mutations add one or more DNA bases. Deletion mutations remove one or more DNA bases. Unless they happen in multiples of 3 bases, insertions and deletions shift the reading frame—which is why they’re also called frameshift mutations. A frameshift changes the grouping of bases into codons, affecting all the amino acids downstream of the mutation. The cell will keep reading until it reaches a stop codon, which may happen earlier or later than in the original sequence.

All living things read genes the same way. They read codons to build proteins according to a Universal Genetic Code. Each 3-letter codon codes for a specific amino acid (or, in three cases, a “stop” codon).

When mutation changes a gene’s DNA sequence, you can use a codon look-up table to predict changes to the protein it codes for. Some codon changes are more impactful than others. For example, since multiple codons code for the same amino acid, some mutations will not change the protein. And when the protein does change, there is a greater impact when the substituted amino acid has a different size and chemical properties (e.g., Glu to Gly) than when it is similar to the original (e.g., Glu to Asp).