Can someone explain the reasoning behind the answers The wild-type sequence for
ID: 91222 • Letter: C
Question
Can someone explain the reasoning behind the answers
The wild-type sequence for bacteriophage gene A is Met-Phe-Ile-Asn-Cys-Ser- Ala-Glu-Gly. The only amino acids necessary for function of this protein are the final three (Ala- Glu-Gly). When full length protein with these final 3 amino acids is produced, functional protein A allows the bacteriophage to infect E coli strain K ("wild-type phenotype"). Without functional protein A, the phage cannot infect strain K ("mutant phenotype"). a. You are working with a newly discovered mutagen, and you wish to determine the base change that it introduces into DNA. Thus far, you have determined that the mutagen chemically alters a single base in such a way that its base-pairing properties are altered permanently. Phage mutant strain #1 is isolated and the sequence of protein A in this phage is determined to be identical to wild-type except for the final amino acid, which is valine. What is the base-change specificity of the mutagen? Explain your answer. Circle your answer. b. Identify the possible anticodons of suppressor tRNAs which could suppress the mutant phenotype of phage strain #1. Assume that the suppressor tRNA anticodon carries a single point mutation compared to the wild-type tRNA. Label 5' and 3' ends of the suppressor anticodons. If more than one anticodon is possible, list all. Circle your answer.Explanation / Answer
Answers:
a. "Point mutations" are small changes in the sequence of DNAbases within a gene.Transitions are mutations in which one pyrimidine (C or T) is substituted by the other and one purine (G or A) is substituted on the complementary strand.
This transition has happend here also. So for the wild type varity the codons could have been GGG, GGC, GGA or TTT, since a change in Purine --> pyrimidine will change the base pairing properties permanently it is expected that this transition mutation had happend to the wild type variety.
b. DNA codons for Valine are GTT, GTC, GTA, GTG, so anticodons are possible fore these would be AAC, CAC, GAC and UAC which could give rise to valine codon through a single point mutation.