For this question, we focus on four parts: I, the gene that produces the repress

Question

For this question, we focus on four parts:

I, the gene that produces the repressor protein;

P, the promoter region where RNA polymerase binds to initiate transcription;

O, the Operator site, where the repressor binds. When the repressor binds, it prevents transcription; and

For this question, we focus on four parts:

I, the gene that produces the repressor protein;

P, the promoter region where RNA polymerase binds to initiate transcription;

O, the Operator site, where the repressor binds. When the repressor binds, it prevents transcription; and

ZYA, the three structural genes, all of which are required for the successful utilization of lactose as a food source.

In the left column of the table below, we indicate the genetic composition at the lac operon of particular strains of E. coli cells. A "+" (plus sign) following the letter indicates the wild-type allele (or normally functioning version of the gene). For I, P, and ZYA, a "-" (negative sign) following the letter indicates the mutant allele (or non-functional version of the gene). For the O allele, a "C" indicates the mutant or constitutive allele. It is not functional in that the repressor cannot bind, but it is functional in that transcription can still occur.

Given the conditions stated in each column, please indicate for each genotype whether lac mRNA is produced and at what level by typing in one of the following words in each cell in the table: Abundant, Minimal, None

Cellular conditions: Genotype Glucose present (low cAMP) and no lactose Glucose present (low cAMP) and lactose present No glucose (high cAMP) and lactose present I+ P+ O+ ZYA+ None Minimal Abundant I- P+ O+ ZYA+ Blank 1 Blank 2 Blank 3 I+ P- O+ ZYA+ Blank 4 Blank 5 Blank 6 I+ P+ Oc ZYA+ Blank 7 Blank 8 Blank 9 I+ P+ O+ ZYA- (a) Glucose present (cAMP low); no lactose; no lac mRNA CAP Repressor (b) Glucose present (cAMP low); lactose present CAP Very little lac mRNA Lactose Induc repressor (c) No glucose present (cAMP high); lactose present CAP-cAMP Lactose Inducer- repressor Abundant lac mRNA Figure 11-17 Introduction to Genetic Analysis, Eleventh Edition © 2015 W. H. Freeman and Company

Explanation / Answer

genotype

Cellular condition

Glucose present(Low cAMP) and no lactose

Glucose present(Low cAMP) and lactose present

Glucose absent(high cAMP) and lactose present

I+ P+ O+ ZYA+

None

Minimal

abundunt

I- P+ O+ ZYA+

Minimal

Minimal

Abundunt

I+ P- O+ ZYA+

None

None

None

I+ P+ Oc ZYA+

Minimal

Minimal

Abundunt

I+ P+ O+ ZYA-

None

Minimal

abundunt

I- will cause no repressor molecule which leads to constitutive promotor clearance

P- will render RNA pol unable to bind with promotor region, therefore, there will be no transcription event.

Oc will not allow binding of repressor protein which leads to constitutive promotor clearance

ZYA- will have defective translated product, therefore, will not have any effect on their transcription

genotype

Cellular condition

Glucose present(Low cAMP) and no lactose

Glucose present(Low cAMP) and lactose present

Glucose absent(high cAMP) and lactose present

I+ P+ O+ ZYA+

None

Minimal

abundunt

I- P+ O+ ZYA+

Minimal

Minimal

Abundunt

I+ P- O+ ZYA+

None

None

None

I+ P+ Oc ZYA+

Minimal

Minimal

Abundunt

I+ P+ O+ ZYA-

None

Minimal

abundunt

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