Question

Wild-type Mutant NH₃-Thr-Lysser-Pro-ser-leu-Asn-Ah-Cout NH₂-Thr-Lys-ser-Pro-Cool Question How many single base pair changes and in what positions would it take to make the mutant from the wild type?

Answer 1

One single base pair changes can convert a codon in to stop codon. Stop codons are UAG,UAA,UGA. The polypeptide stops at Pro. That means the codon coding serine has mutated in the DNA. Serine is coded by codons--UCA,UCU,UCC,UCG. One of these codons of RNA can code for serine. The DNA codons for this amino acid are --AGT, AGA, AGG,AGC. Mutations occur in DNA strand. So, one of these codons which code serine in the polypeptide shown must have got mutated at just one point in the second position.

AGT which codes for serine, must have got mutated to ACT. G must have got replaced by C, making it ACT. This codon ACT transcribes it in to UGA. Since UAG is a stop codon for protein synthesis, protein synthesis stops at UGA. So the polypeptide strands becomes short.

So one point mutation at the second position of the 5th codon which codes for serine got mutated. It is a transversion mutation. Since a pyrimidine got replaced by a purine.