(6 points) A piece of DNA encoded the following protein product N- met-pro-cys-

Question

(6 points) A piece of DNA encoded the following protein product

N- met-pro-cys- gln- arg- trp-trp-C

Researchers were for some mysterious reason unable to directly sequence the DNA. So they took the indirect approach. They made a mutation, translated the sequence and used the change in the protein sequence to figure out the original DNA sequence. The mutant DNA they made had just one change – either one nucleotide added, one removed, or one changed. Deduce the original DNA sequence, and fully explain your reasoning, including where the mutation is and what type of mutation it is. If you are unable to be sure about a certain sequence, use a / to indicate this. For example asp is encoded by GAU and GAC. If you couldn’t be sure of the DNA sequence where it encoded asp, you would write that part as GAT/C, showing that are you aren’t sure if the DNA sequence is GAT or GAC. In writing out the DNA sequence, show both strands, label the 5’ and 3’ ends and label the coding and template strands. Here is the mutant protein sequence:

N-met –ala-leu-pro-lys-val-val-val-arg-C

Explanation / Answer

Since one amino acid is encoded by more than one type of codons, the DNA sequence of the original and the mutated sequences can be found as below:

DNA sequence of the initial sequence:

5' ATG CCA/T/G/C TGT/C CCA/G AGA/G TGG 3'

3' TAC GGT/C/G/A ACA/G GGT/C TCT/C ACC 5'

DNA sequence of the mutated sequence:

5' ATG GGA/T/C/G CCA/T/G/C CCA/T/G/C AAA/G GTA/T/G/C GGA/T/G/C GGA/T/G/C AGA/G 3'

3' TAC CCT/A/G/C GGT/A/C/G GGT/A/C/G TTT/C CAT/A/C/G CCT/A/C/G CCT/A/C/G TCT/G 5'

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