As a student project, you have isolated six new mutant strains of E. coli with a

Question

As a student project, you have isolated six new mutant strains of E. coli with altered behavior of the lactose operon. The strains are listed in the table below, together with their phenotypes (with regard to significant ?-galactosidase synthesis) in three specific situations.

Columns 1 and 2 present the phenotypes of each mutant haploid strain. In column 1, the mutant is in an otherwise wild-type genome. In column 2, the genome also carries a nonsense-suppressor mutation (that is not present in the genome of column 1).

In column 3, each partial diploid was constructed by introducing a plasmid with the entire lac operon (including I, but not crp) from the original mutant strain into host cells whose complete bacterial chromosome is wild-type except for the lacZ gene, which carries a small deletion.

Part A

Which mutant strain is most likely to have a small deletion in the I? gene, resulting in the loss of functional repressor protein?

A
B
C
D
E
F

Part B

Which mutant might be a small deletion in the operator region of the ?lac? operon?

A

B

C
D
E
F

Part C

Which mutant might be a small deletion in the promoter of the ?lac? operon?

A
B
C
D
E
F

Part D

Which mutant might be a frameshift near the translation start site in the structural gene for ?-galactosidase?

A
B
C
D
E
F

Part E

Which strain might have a nonsense-suppressor-sensitive mutation in the ?crp? gene?

A
B
C
D
E
F

Part F

Which strain might have a nonsense-suppressor-sensitive mutation in the ?-galactosidase gene?

A
B
C
D
E
F

Part G

Which strain might contain an ?I?S? ?mutant gene product?

A
B
C
D
E
F

please explain thanks

2 3 mutant strain studiec mutant in wild-type backgroundbackground background mutant in suppressor mutant/Z partial diploid inducible constitutive constitutive no activity inducible inducible constitutive no activity inducible no activity constitutive constitutive no activity no activity constitutive nducible no activity inducible

Explanation / Answer

A)

The strain ‘D’ is most likely to have a small deletion in the ‘I’ gene, resulting in the loss of functional repressor protein. This is because the strain ‘D’ is inactive in wild type, mutant strain and in partial diploid cells. Option 4 is correct.

B)

The strain ‘F’ mutant might be a small deletion in the operator region of the lac operon. This is because the strain ‘F’ is inactive in wild type strain and partial diploid strain. The mutant strain is inducible due to suppressor mutation. Hence, option 6 is correct.

C)

The strain ‘D’ mutant might be a small deletion in the promoter of the lac operon. This is because the strain ‘D’ is inactive in wild type, mutant strain and in partial diploid cells. Option 4 is correct.

D)

The strain ‘A’ mutant might be a frame shift near the translation start site in the structural gene for -galactosidase because it is inactive in wild type but inducible in mutant and partial diploid cells. Hence, option 1 is correct.

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