2. You are studying two missense mutations in a gene (lets call it X) that affec

Question

2. You are studying two missense mutations in a gene (lets call it X) that affects S. pneumoniae, such that the bacteria are not the normal S form, but are instead the R form (remember the Griffiths experiment!). Because of technical limitations you cannot determine the nucleotide sequence of the gene but you are able to sequence the protein that is affected by the mutation and determine its complete amino acid sequence. You do know that the mutagen only induces single nucleotide missense mutations and does not cause insertions or deletions of nucleotides. A. Mutation 1 causes amino acid 17 of Protein X to be Methionine (Met) instead of Arginine (Arg). What are the possibilities for the DNA sequence of the wild type X gene at the codon that nomally encodes amino acid 17? B. You identify another mutation (Mutation 2) that results in an R form, which causes amino acid 28 of protein X to be a Tryptophan (Trp) instead of a Glycine (Gly). You mutagenize S. pneumoniae that carry Mutation 2 and look for revertants that are now S form. You isolate a S. pneumonia that has Mutation 3 acid 28. and when you sequence this revertant line you find that it has a Serine at amino What are the possibilities for the DNA sequence of the wild type X gene at the codon that normally encodes amino acid 28. What about for this same codon in Mutation 2 and 3? Explain your reasoning. WT codon for position 28 Mut2 don for position 28: Mut3 codon for position 28:

Explanation / Answer

Missense mutation is a point mutation in which single nucleotide change will leads to a codon that codes for a different amino acids.

A) In case of mutation 1 amino acid 17 of protein X converted from Arginine to methionine.

Methionine coded by codon ATG

Arginine codedd by 6 codon CGT, CGC, CGA, CGG, AGA, AGG

wild type codon for amino acid 17 was supposed to be the AGG in nucleotide G at position 2 was converted into T.

B) In case of mutation 2 amino acid 28 of protein X converted from glycine to tryptophan.

Tryptophan coded by codon ATG

Glycine codedd by 4 codon GGT, GGC, GGA, GGG

wild type codon for amino acid 28 was supposed to be the GGG in nucleotide G at position 1 was converted into T.

Codon for Mutation 2 was supposed to be TGG which codes for amino acid Tryptophan.

In mutation 3 , serine was found at position 28 instead of tryptophan in mutated 2 protein X.

Codon for Mutation 3 was supposed to be TCG which codes for amino acid Serine. Nucleotide G at position 2 was converted to C.

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