The hypothetical BSc operon of bacteria encodes the HD enzyme and the P enzyme.
ID: 279785 • Letter: T
Question
The hypothetical BSc operon of bacteria encodes the HD enzyme and the P enzyme. Expression of this operon is regulated in response to substance X and substance Y. Five different mutants have been isolated that show abnormal regulation of expression of the BSc operon. The table below shows the level of enzyme activity for these different mutants. First the bacterial cells were incubated in minimum medium, then compound 1 was added, and then compound 2 was added after further incubation: And then after substance Y added Minimal medium After substance X added HD enzyme Penzyme P enzyme high high HD enzyme HD enzyme P enzyme Cells ?? low low low zero low zero low mutant 1 mutant2 mutant 3 mutant 4 mutant 5 ze ro low low low high high ze ro [1 markl a) b) c) Which observations indicate that the BSc operon is inducible? Which observations indicate that the BSc operon is also repressible? Which mutant shows gene expression consistent with being a loss-of-function mutation in: [1 markl i. the promoter of this operon ii. the DNA sequence iii. the DNA sequence iv. the gene encoding HD enzyme v. the gene encoding P enzyme bound by the positive regulator bound by the negative regulator 7 marks]Explanation / Answer
a.Mutant 2 shows that BSc operon is inducible as the mutation has resulted in no expression of HD and P enzyme in presence of compound X whereas wild type is induced by compund X
b. Mutant 4 behaves more or less like wild type and shows that upon addition of X, BSc operon gets activated, whereas compound Y leads to repression of the same.
c.(iii) DNA sequence operated by a negative regulator as the transcription does not take place in this case.
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