Question

1. Tryptophan (Trp) is encoded by the codon UGG. Suppose that a cell was treated with high levels of 5-Bromouracil such that mutations were induced at Trp codons. Would you expect that these mutations would results in a non-sense mutation, a silent mutation, a missense mutation. Explain your answer.What is a tautomeric shift and explain how it contributes to transition mutations?

2.Draw the structure of the rare tautomeric enol form of guanine. Draw the structure of the monophosphate deoxynucleotide which can base-pair with this form of guanine. Indicate which atoms of the two nucleotides form hydrogen bonds during base-pairing.

3.The -10 core promoter of the lac operon gene has the sequence TATGTT. Describe an example of a base substitution mutation which would lead to increase transcription of the gene. Explain whether this mutation would increase or decrease the fitness of the organisms.

4.Explain why open reading frame mutations caused by intercalating chemicals such as acridine orange are more likely to have a severe affect on phenotype when compared to mutations caused by deaminating chemicals such as nitrous acid.

Answer 1

1. 5-Bromouracil induces a point mutation by changing base pair either A-T to G-C or G-C to A-T. In case of trp codon UGG, possible mutants are UAG, UAG or UAA; all are stop codons. Hence, the treatment of the cell with high levels of 5-Bromouracil will result in non-sense mutation because of incorporation stop codons.

R. Ghuanime (enel) in alternate tau)owers ondingwt fmn it frms ·3d.egen bonding with C uawi ne 2. with R (TMp