S9-Mutation Homework and Answer Key

S9-Mutation Homework and Answer Key

INSTRUCTOR NOTES

I give the students this assignment at least five days before the class meets for the week 4 laboratory (Supplemental file S8) and I incorporate this assignment into the week 4 in-laboratory discussion. While I do check to see that the students have attempted the assignment prior to the laboratory meeting, I allow the students to correct the assignment as we discuss it during the laboratory session.

To successfully complete this pre-laboratory assignment the students will need to have prior knowledge of how deletions of DNA base pairs in the DNA result in frameshift mutations at the protein level. If the instructor has not yet covered frameshift mutations in class it is probably best to complete this activity during the week 4 laboratory session rather than assign it as homework. Even if students have prior knowledge of base pair deletion and frameshift mutations some students will still need guidance from the instructor before they can complete the assignment. The answer key is provided at the end of this assignment.

Student Homework assignment

Please complete the following problems and bring them to the laboratory session this week.

1. Translate the following RNA sequence from left to right starting with the underlined AUG:

AUGUGCCCGACGAGGUACAUGAGUAGGACACCCUGA

Assume that a DNA mutation occurs that deletes the sixth base in the corresponding RNA sequence (a cytosine). Write the sequence of the protein that is made when the mutant RNA is translated.

Describe the affects that a single base pair (bp) deletion in the DNA has on the protein.

2. The following represents the normal sequence of a protein and a mutated version of the same protein. Determine what single bp mutation occurred at the DNA level that resulted in the mutant version of the protein. Clearly show your work.

Normal Met-Gln-Trp-Asn-Leu-Ser

Mutant 1 Met-Gln-Trp-Lys-Pro

instructor Answer Key

1. Translate the following RNA sequence from left to right starting with the underlined ATG:

AUG UGC CCG ACG AGG UAC AUG AGU AGG ACA CCC UGA

Met Cys Pro Thr Arg Tyr Met Ser Arg Thr Pro

Assume that a DNA mutation occurs that deletes the sixth base in the corresponding RNA sequence (a cytosine). Write the sequence of the protein when the mutant RNA is translated.

Met Cys Arg Arg Gly Thr

Describe the effects that a single base pair (bp) deletion in the DNA has on the protein.

Single base deletions in the DNA change the amino acid sequence starting where the DNA base is deleted. This is a frameshift mutation at the protein level.

2. The following represents the normal sequence of a protein and a mutated version of the same protein. Determine what single bp mutation occurred at the DNA level that resulted in the mutant version of the protein. Clearly show your work.

R=purine

Y=pyrimidine

N=any nucleotide

To solve this problem, first use the protein sequence to determine as much of the RNA sequence as possible for both the normal and mutant.

Normal Met-Gln-Trp-Asn-Leu-Ser

RNA AUG CAR UGG AAY CUN AGU

or or

UUR UCN

Mutant 1 Met-Gln-Trp-Lys-Pro

RNA AUG CAR UGG AAR CCN UAG

Now compare the two RNA sequences to determine the single bp change that occurred in the mutant. By carefully comparing the sequences, one can see that a purine (R) was added at the third base position in the fourth codon. That is, the AAY codon in the normal RNA is AAR in the mutant and the bases in the mutant have shifted by one.

Further comparisons of the normal and mutant RNA sequences will allow one to determine the exact normal and mutant RNA sequences.

Normal Met-Gln-Trp-Asn-Leu-Ser

RNA AUG CAR UGG AAY CUN AGU (or UCN)

Mutant 1 Met-Gln-Trp-Lys-Pro

RNA AUG CAR UGG AAR CCN UAG