Question

1. You have used a mutagen to induce mutations in a DNA sequence.  If the original DNA strand is 5'-ATGGGACTAGATACC-3', then which of the following represents a nonsense mutation? (1pt)

1. 5'-ATGGGTCTAGATACC-3'
2. 5'-ATGCGACTAGATACC-3'
3. 5'-ATGTGACTAGATACC-3'
4. 5'-ATGGGACTAAGATACC-3'

2. A mutation that changes a codon sequence, and subsequently changes the amino acid that should have been placed at that point in the polypeptide chain, is called a… (1pt)

1. silent mutation
2. frameshift mutation
3. missense mutation
4. nonsense mutation

3. Excision repair corrects DNA by (1pt)

1. correcting A=T to C=G transitions
2. detecting, removing, and replacing damaged or incorrect bases or nucleotides in a single strand of DNA
3. removing a double-stranded fragment of damaged DNA
4. excising the incorrect base from a nucleotide
5. removing extraneous groups such as methyl or oxygen added by mutagens

4. Suppose there is a protein of 50 amino acids.  The 10^th codon is a glutamine codon, CAG.  Below are the new codons produced by three different mutations.  From what you know about the genetic code in general, indicate which mutation is likely to be the most serious, the least serious, or the one of intermediate impact.  In a few words, explain why.

(1pt) TAG                      

(1pt) CGG  

(1pt) CAA                      

Answer 1

Option d is a nonsense mutation. A nonsense mutation means a genetic mutation had occured in a DNA that results in a shorter unfinished protein product. DNA is made up of nucleotides. Usually during protein formation a DNA is read as 3 nucleotides and they are called codons. Each codon corresponds to a particular amino acid. In case of a nonsense mutatuon it results in the formation of a stop codon. Which means protein formation stops because of the change in the normal nucletide number.