Note whether, in the following strains of E. coli , B-galactosidase will be: A)
ID: 260472 • Letter: N
Question
Note whether, in the following strains of E. coli, B-galactosidase will be:
A) Abundant 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 only in the presence of sucrose; or
E) Absent in both the presence and absence of lactose.
Strain 1: Wild-type
Strain 2: o(c)
Strain 3: i(s) p(-)
Strain 4: p(-) o(c)
Strain 5: i(s) o(c) / i(+) o(+)
Strain 6: i(-) p(+) / i(+) p(-)
Strain 7: i(-) p(+) o(c) / i(+) p(-) o(+)
Explanation / Answer
Strain 1, Wild type: I(+) P(+) O(+)
B-galactosidase will be abundant only in the presence of lactose. It is because presence of lactose will inhibit the repressor protein of Lac operon.
Strain 2: O (c)
B-galactosidase will be abundant in both the presence and absence of lactose. It is because, due to a mutation in the operator sequence, repressor protein could not bind to it. Hence presence or absence of lactose has no impact on the constitutive expression of B-galactosidase.
Strain 3: I(s) P(-)
B-galactosidase will be absent in both the presence and absence of lactose. The lactose binding site of repressor is mutated hence presence or absence of lactose has no impact the repressor protein. And also the promotor region is mutated, hence the enzyme responsible for transcription could not bind to it.
Strain 4: P(-) O(c)
B-galactosidase will be absent in both the presence and absence of lactose. The promotor region is mutated, hence the enzyme responsible for transcription could not bind to it.
Strain 5: I(s) O(c) / I(+) O(+)
B-galactosidase will be absent in both the presence and absence of lactose. The lactose binding site of repressor is mutated hence presence or absence of lactose has no impact the repressor protein.
Strain 6: I(-) P(+) / I(+) P(-)
B-galactosidase will be abundant only in the presence of lactose. It is because presence of lactose will inhibit the repressor protein of Lac operon.
Strain 7: I(-) P(+) O(c) / I(+) P(-) O(+)
B-galactosidase will be abundant only in the presence of lactose. It is because presence of lactose will inhibit the repressor protein of Lac operon.
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