Question

In this problem you will explore how to solve problems involving partial diploid lac operon bacterial strains.

Bacterial strains that are "partially diploid" have two copies of the lac operon because they aquired a plasmid carrying just the lac operon region. One copy of the lac operon region is on the recipient's bacterial chromosome, and the other copy is on the F' plasmid that was introduced into the cell by conjugation. Partial diploid genotypes are written with the F' segment first and the recipient chromosome next.

You create a lac operon partial diploid with this genotype:

F' I⁺ P⁺ O^c Z⁻ Y⁺ / I⁻ P⁺ O⁺ Z⁺ Y⁻

To determine which genes are transcribed and under what conditions, you need to first consider each genotype separately, and then together.

Part C

Now, for each region of the lac operon on the bacterial chromosome, I⁻ P⁺ O⁺ Z⁺ Y⁻, determine whether the region is wild type (that is, it produces a functional protein or it's a correct protein binding sequence) or whether the region is mutated.

Correct answers: The promoter sequence is correct/functional, The operator sequence is correct/functional, Beta-galactosidase is produced from the lacZ gene.

PLEASE ANSWER PART D USING ANSWERS FROM PART C

Part D Use the information from Part C to determine how the operon is regulated for this genotype (I- P+ O+ Z+ Y-). PLEASE SELECT ONE ANSWER!! a) Operon is constitutive; lacZ is transcribed even when lactose is absent. b) Operon is noninducible; lacZ is never transcribed, even in the presence of lactose. c) Operon is repressible; lacZ is only expressed in the absence of lactose. d) Operon is inducible; lacZ is transcribed only in the presence of lactose.

Answer 1

part C

I+ P+ Oc Z- Y+ : this genotype encodes for a repressor. however, operator has a constitutive mutation, hence, repressor cannot bind to operator. operator allows transcription constitutively so that permease is produced continuously but not beta-galaactosidase.

I- P+ O+ Z+ Y- : this genotype does not encode for repressor. therefore beta galactosidase is encoded continuously.

However, in diploid condition, the repressor encoded in F' diffuses and acts in trans. therefore, permease is encoded contiinuously whereas betagalactosidase is encoded in presence of lactose.

part D

considering only one genotype, I- P+ O+ Z+ Y- , this does not code for repressor. therefore, this operon acts as constitutive and produces betagalactosidase constitutively.

option A. operon is constitutive; lacZ is transcribed even when lactose is absent.