Please answer whole question, I will leave thumbs up! You are studying two misse
ID: 210913 • Letter: P
Question
Please answer whole question, I will leave thumbs up!
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 normally 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 and when you sequence this revertant line you find that it has a Serine at amino acid 28.
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 codon for position 28:
Mut3 codon for position 28:
Explanation / Answer
1- Methionine is coded by AUG and arginine is coded by AGG codon.
So if we see there is only one base pair difference between methionine codon and arginine codon. i.e. G is replaced with U
2- Glycine is coded by GGU, GGA, GGG, GGC.
tryptophan is coded by UGG.
Serine is coded by AGU, AGC, UCU, UCC, UCG, UCA.
Since there is only point mutation so there will be a change in only one nucleotide. So only one combination will make sense which is given below
So initial codon for glycine was GGG, it was mutated into tryptophan codon UGG. This tryptophan codon is mutated into UCG
WT codon for position 28: GGG
Mut2 codon for position 28: UGG
Mut3 codon for position 28: UCG