1O. You have a bacterial strain that carries a point mutation in the laczZ gene.

Question

1O. You have a bacterial strain that carries a point mutation in the laczZ gene. As a result, the strain is Lac G) d codes for a You construct two derivatives of strain #1 Each carries a plasmid. In strain 02, the plasm glutamine tRNA that recognizes the "amber" termination codon, UAG. In strain a serine tRNA that recognizes the amber codon. You find that strain #2 is Lac (+ Lac (-). (4) a. What do you #3, the plasmid codes for remains ), whereas #3 conclude about the original lacZ mutation based on strain #2 being Lac (+) Explain. What do you conclude about the protein based on strain #3 being Lace* Explain (4) b

Explanation / Answer

Ans:

According to the question, # strain1 has a point mutation for which it is lac-.

a) Now here, the plasmid codes for glutamine tRNA which recognizes the amber termination codon, UAG. #Strain 2 becomes lac+. Now, this can mean either that the original sequence was CAG coding for glutamine, a point mutation resulted in it to be transformed into a stop codon or the original sequence used to code for glutamic acid which is closer to glutamine in a chemical sense i.e. GAG, the point mutation occurred in the first nucleotide of the codon resulting in the same. Here, after adding the plasmid the normal protein with glutamic acid or gamine could be translated, hence it became lac+.lut

b) #strain 3 had a serine tRNA which could recognize the amber codon, but the resulting protein was non-functional hence it became lac-, this could suggest that the resulting protein has a motif which requires glutamine instead of serine for its enzymatic activity or correct folding.

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