Question

Note whether in the following strains of E. coli, B-galactosidase will be:

(A) Absent in both the presence and absence of lactose;

(B) Abundant only in the absence of lactose;

(C) Abundant only in the presence of lactose;

(D) Abundant in both the presence and absence of lactose; or

(E) Abundant only in the presence of glucose.

I. i(-);

II. p(-)o(c);

III. i(-)p(+) / i(+)p(-);

IV. i(s)p(+)o(c) / i(+)p(-)o(+).

Answer 1

I. i(-) : (D) Abundant in both the presence and absence of lactose.

Since it is lac i -, no repressor will be formed to bind the operator,so beta galactosidase will be formed both in presence and absence of lactose.

II. p(-)o(c):   (A) Absent in both the presence and absence of lactose;

Constitutive operator will not allow repressor to bind but as promoter is absent/mutated , no beta galactosidase will be formed in presence or absence of lactose.

III. i(-)p(+) / i(+)p(-):   (C) Abundant only in the presence of lactose

In presence of lactose only,beta galactosodase will be formed as repressor fails to bind to operator.

IV. i(s)p(+)o(c) / i(+)p(-)o(+): (D) Abundant in both the presence and absence of lactose

In this case, always beta galactosidase will be formed in presence or absence of lactose.