In a bacterial operon similar to the lac operon, the R gene codes for a represso
ID: 16686 • Letter: I
Question
In a bacterial operon similar to the lac operon, the R gene codes for a repressor, P is a promoter, O is an operator, and A is a structural gene for one of the enzymes in the operon. The allele R- represents lack of repressor, for O' the repressor cannot bind the operator, and A- is a mutation leading to lack of enzyme activity. In the following genotypes, determine if the cell will show enzyme A activity in the absence and in the presence of the inducer. (The “+” indicates a functional gene or sequence.)A. R+ P- O+ A+
B. R+ P+ O' A+
C. R- P+ O+ A+
D. R- P+ O+ A-
E. R+ P+ O' A-
F. R- P+ O+ A+
G. R- P+ O' A+
H. R- P- O' A+
I. R+ P+ O+ A+
Explanation / Answer
A. R+ P- O+ A+ = No expression of the enzyme A will take place and consequently no activity irrespective of presence or absence of inducer. B. R+ P+ O' A+ = Constitutive expression of enzyme A will take place irrespective of presence or absence of inducer ( i.e- either inducer is absent or present) C. R- P+ O+ A+ = Constitutive expression of enzyme A will take place irrespective of presence or absence of inducer ( i.e- either inducer is absent or present) D. R- P+ O+ A- = Expression of the enzyme A will take place but enzyme will not be active because of the mutation irrespective of presence or absence of inducer. E. R+ P+ O' A- = Constitutive expression of enzyme A will take place irrespective of presence or absence of inducer ( i.e- either inducer is absent or present) but enzyme will not be functional because of mutation. F. R- P+ O+ A+ = Constitutive expression of enzyme A will take place irrespective of presence or absence of inducer ( i.e- either inducer is absent or present) and enzyme will be functional and its activity can be seen. G. R- P+ O' A+ = Constitutive expression of enzyme A will take place irrespective of presence or absence of inducer ( i.e- either inducer is absent or present) and enzyme will be functional and its activity can be seen. H. R- P- O' A+ = No expression of the enzyme A will take place and consequently no activity irrespective of presence or absence of inducer. I. R+ P+ O+ A+= expression will take place in the presence of inducer and it will not take place in the absence of inducer.