Question

8. In afictitious bacteria, an operon induced by the presence of compound Z. A diagram of this operon, its regulatory proteins and sites is show below gene X gene A gene B · 2x-promoter for the regulatory protein . X-gene for the regulatory protein · P = promoter for AB gene . S sequence important for regulation by compound Z A= structural gen e for enzymeA B-structural genefor enzyme B The following table shows thegenotypes of different strains of thefictitious bacterium with wild type (normal) AB operon and various mutant AB operons and the number of molecule of proteins A and B per cell in absence or presence of compound Z (-Z or +Z). The symbol "+" indicates that the gene or control element is functional (wild type) and"-"that the gene or control element is not functional. Assume any genes not listed are functional Strain -Z Expression Wild type 200 Mutant 1 200 200 Mutant2 0 0 Mutant 3 200 200 a.Foreach strain in the table, label the expression as either inducible, uninducible or constitutive b. Based on the data in the table, does the regulatory protein Zact as a repressor or an activator ofthe AB operon? Explain your answer.

Answer 1

a.
Mutant 1 is inducible.
The presence of Z causes expression of the operon.

b.
Mutant 1 is constitutive.
The presence or absence of Z has no difference.

c.
Mutant 2 is uninducible.
As the promoter is inactive, it can not be induced.

d.
Mutant 3 is constitutive.
As the repressor binding site is mutated, repressor can not repress the operon.

The presence of Z causes expression of the operon. So, it is an inducer.