Science 10 with CSS teacher

Making a Mutation

Introduction

You might recall that genes are long sections of a DNA molecule, and that they can contain very large numbers of base pairs. Would it really be so bad if just one of these was changed by a mutation?

This guided practice will give you a chance to see how each type of gene mutation—deletion, addition, and substitution—can occur.

Instructions

If you can think of a gene as a sentence, then the four DNA bases would be the letters that make up that sentence. In a moment, you will use these bases to complete an activity; but first, read this comparison between the genetic code and the English language.

Just like in English sentences, letters must be placed in a specific sequence, or they will not make sense. Consider the following model of a gene sequence:

Remember that bases are 'read' in sets of three—these codons compare to the words in the sentence:

Type of Mutation	Effect on our Sample Sentence	How this Model Compares to Actual Gene Mutations
Addition	The rre ddo gsa wth eca tea tth efa tra t (An extra letter ”r” is added to the word “red.”)	When you add a 'letter', the sentence does not make sense any more. In DNA, an addition mutation can make a gene's protein-building instructions unreadable.
Deletion	The edd ogs awt hec ate att hef atr at (The letter “r” is removed from the word “red.)	The effect is similar to that of an added base—the gene 'sentence' becomes unreadable.
Substitution	The bed dog saw the cat eat the fat rat (The letter “b” replaces the letter “r” in the word “red.”)	Most of our sentence is still readable. In DNA, if one base replaces another, the gene could still code for the correct protein.

Now, answer the following questions using this DNA sequence:

1. a. Separate this DNA sequence into codons (groups of three bases each).

   b. What is the amino acid sequence that would correspond to this DNA sequence? To find the answer, use the chart of codons provided.

   Here is the mRNA base sequence that corresponds to the DNA sequence provided above:

   GGC UAU CGU AAA

   

   Solution? click here

   a. CCG ATA GCA TTT

   b. Glycine, Tyrosine, Arginine, Lysine

2. a. Rewrite the sequence to show how it would look if the first “G” was deleted.

   b. The mRNA sequence that corresponds to this mutated DNA sequence is GGU AUC GUA AA. What sequence of amino acids does this code for?

   Solution? click here

   a. CCA TAG CAT TT

   b. Glycine, Isoleucine, Valine. The remaining two bases cannot code for an amino acid.

3. a. Rewrite the original DNA sequence to show how it would look if another 'G' was added next to the first 'G'.

   b. The mRNA sequence that corresponds to this mutated DNA sequence is GGC CUA UCG UAA A. What sequence of amino acids does this code for?

   Solution? click here

   a. CCG GAT AGC ATT T

   b. glycine, leucine, serine, stop. The last bases cannot code for an amino acid.

4. a. Rewrite the original DNA sequence to show how it would look the first “G” was replaced by “C.”

   b. The mRNA sequence that corresponds to this mutated DNA sequence is GGG UAU CGU AAA. What sequence of amino acids does this code for?

   Solution? click here

   a. CCC ATA GCA TTT

   b. Glycine, tyrosine, arginine, lysine

5. Based on your comparison of the amino acid sequences produced by DNA mutations in questions 2–4, which do you think would be the least harmful mutation to a cell? Why?

   Solution? click here

   Substitution mutations are least likely to be harmful because changing one base would only change one amino acid. In this example, there was no change at all, even though a mutation had occurred.

When you are done, please go to this site - Learn Genetics. When you have completed the activity take a screenshot of your work and email it to me.