Read instructions 1-6 before you begin and think about the relationships between

Question

Read instructions 1-6 before you begin and think about the relationships between

the various steps!

Cystic fibrosis is a life threatening genetic disease cause by mutation in a

gene called CFTR.CFTR encodes a transmembrane protein pictured below. It is

in the plasma membrane and is a transporter for chloride and thiocyanate

ions. People with cystic fibrosis have a mutation in this gene which renders

CFTR nonfunctional. This creates a thick mucus in the lungs and patients are

prone to bacterial infections. This leads to a life expectancy of roughly 40

years.

Below is part of the CFTR gene. Use it to answer the following questions.

5’-gagtagtagg tctttggcat taggagcttg agcccagacg gccctagc 3’

1. Draw the complementary sequence as well as the mRNA it would produce assuming it is

all an exon.

2. Translate the sequence of the mRNA assuming that the reading frame starts gag

3. Many separate mutations can cause cystic fibrosis. You suspect a patient has a mutation

in the region of DNA above. Write the sequences of the PCR primers that would replicate that

entire region.

4. Suppose you find a frameshift mutation. Write what this would look like in the sequence and

how it changes the protein. Why would it affect function?

5. Suppose you find a missense mutation. Write what this would look like in the sequence and how

it changes the function of the protein.

6. Suppose that you don’t find a silent mutation above. Propose a hypothesis for how the silent

mutation is causing a the disease.

Explanation / Answer

1. The complimentry sequence would be:

5’-gagtagtagg tctttggcat taggagcttg agcccagacg gccctagc 3’

3'-ctcatcatcc agaaaccgta atcctcgaac tcgggtctgc cgggatcg 5'

the mRNA would be : 5' gaguaguagg ucuuuggcau uaggagcuug agcccagacg gcccuagc 3'

2. If the reading frame starts from 5' GAG then the entire mRNA could be translated as :

5' A R A V W A Q A P N A K D L L L 3'

3. primers are the sequences that are complimentary to the DNA region of our interest so that it could bind to them, therefore in the above region the forward and reverse rimers would be as follows:

reverse primer:

3'cgggatcg5'

5’-gagtagtagg tctttggcat taggagcttg agcccagacg gccctagc 3’

forward primer :

5' gagtagtagg3'

3'-ctcatcatcc agaaaccgta atcctcgaac tcgggtctgc cgggatcg 5'

4. If we get a frameshift mutation, then the mRNA seqquence can look like this:

5' gaguaguagg ucuuAuggcau uaggagcuug agcccagacg gcccuagc 3'

so the point at which we inserted the A, beyond that the entire sequence would change that would also lead to change in no of codons and the amino acid that are translated.

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