Question

Shown below are relevant genes and sites from various E. coll strains. Note: + designates the wild-type gene or site that is fully functional, and - designates a deletion of that gene or site; laco means all operators (Oj, 0, and Oy) are functional; assure all other genes and sites not listed are wild-type and functional (including locA). In some cases, a plasmid caintaining a wild-type functional gene or site was transformed into the E. coli strain. The strains were grown with or without glucose, and with or without lactose (for example, with glucose and without lactose is indicated by +/-). Indicate (Yes or No) whether maximum transcription at the chromosomal lac operon promoter occurs in the strain indicated under the conditions given. Chromosome Plasmid Glucose/Lactase CAP Bound? Lacl Bound? Maximum Transcription? crpt lacr lacot lacz licy Nane - + crpt lac lacot lacz lacr lacrt + / - crpt facit laco laczt lanc Nane -- crat lacht laco laczt lacr torrt Junt lacot +/+ tottur Nana crplacrt lacot laczt lacr we +/- watott crplac.lt lacot laczt lacr crpt + / + titative crpt loc lacot lacZ lacr None Nane tart crpt lacrt lacot lacz lacr lacz tartat crpt lacrt lacot lacz lace None crpt lacrt lacot lacZ lace laczt crpt sacrt lacot laczt iacy None - / + crpt sacrt lacot lacztacy lazy +/- Submit Answer Tries 0/99 Post Discussion Send Feedback

Answer 1

Let us first stablish what each element in the operon does:

- crp: This is an inductor of promoters, it promotes transcription, and it is positive in all the strains here

- lac I: This is the sequence to produce the repressor protein, if this sequence is defective then the repressor does not exists and the transcription is constitutive

- lac O: This is the operator site that attaches to the repressor, when the repressor is attached transcription is not possible. If lacO is defective then the repressor cannot bind and transcription is constitutive

- lac Z: Encodes for the enzyme that cleaves lactose

- lac Y: Encodes for the lactose transporter into the cell

- Glucose: Its absence binds the CAP to the operon, it activates the operon

- Lactose: Its presence removes the repressor from the operator and the operon is thus transcribed

Now let us address each case:

Case	CAP?	lacI?	Maximum?
1	Yes	No	Yes
2	No	Yes	No
3	Yes	No	Yes
4	No	No	Yes
5	No	Yes	No
6	No	No	No
7	No	Yes	No
8	Yes	No	Yes
9	No	Yes	No
10	Yes	No	No
11	Yes	No	No
12	No	Yes	No

The CAP binding depends only on the glucose presence/absence.

The lacI binding depends on both the lacI state and the lacO state, and in the presence of lactose.

The maximum transcription requires for the CAP to be bound but the lacI to not be bound, and reuires for both lac Z and lac Y to be wildtype.

The addition of a wildtype allele in a plasmid will bring the normal function of such allele.