Consider E. coli cells with thefollowing mutations. What effect would each mutation have on theexpression of the lac operon (assuming no glucose is present)? Makesure to justify your answer. (A) A mutant lac operator that cannot bind repressor (1pt) (B) A mutant lac repressor that cannot bind to allolactose(1pt) (C) A mutant lac promoter that cannot bind CAP-cAMPcomplex(1pt) Just to clarify, A, B, and C are situations, and the question isasking what would happen in each situation. Thanks

OneClass: Consider E. coli cells with thefollowing mutations. What effect would each mutation have on...

In E.coli the lac operon is controlled by the presence or absence of both lactose and glucose. The lac repressor only allows expression in the presence of lactose, and it is also only activated when glucose levels are low, such that the lac operon is on when lactose is present but glucose is not.

You have cells that are mutant in the gene coding for the Lac repressor (I-). These cells lack the Lac repressor under all conditions. For these mutant cells, state whether the Lac operon will be switched on or off in the following situations, whether the lac repressor (I) is bound to the operator, and whether CAP-cAMP is bound upstream of the promoter.

a. in the presence of glucose and lactose

b. in the presence of glucose and the absence of lactose

c. in the absence of glucose and the absence of lactose

d. in the absence of glucose and the presence of lactose

1. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a Êº+Êº or a Êº-Êº whether Î²-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype C: Is Oc Z+/ FÊ¹ I + O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

2. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a Êº+Êº or a Êº-Êº whether Î²-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype D: I- O+ Z+/ FÊ¹ I- O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

3. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a Êº+Êº or a Êº-Êº whether Î²-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype E: I + O+ Z+/ FÊ¹ I + O+ Z+
KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell

c. +,-

ceruleantiger445

1. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a Êº+Êº or a Êº-Êº whether Î²-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype A: I + O+ Z+/ FÊ¹ I - O+ Z+

KEY:

I+ = wild-type repressor
I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell for certain

c. +,-

2. The following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/).

The possible answers indicate with a Êº+Êº or a Êº-Êº whether Î²-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)

Genotype B: I - Oc Z+/ FÊ¹ I - O+ Z-

KEY:

I+ = wild-type repressor

I- = mutant repressor (unable to bind to the operator)
Is = mutant repressor (insensitive to lactose)
O+ = wild-type operator
Oc = constitutive operator (insensitive to repressor)

a. +,+ d. -,+

b. -,- e. cannot tell for certain

c. +,-

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