4/2/2018 11:55 PM 55.4/100 Question 9 of 14 Available Due Dat Late su 3 Sapling

Question

4/2/2018 11:55 PM 55.4/100 Question 9 of 14 Available Due Dat Late su 3 Sapling Learning Lactose metabolic activity in the lac operon is in the image below Pon ON OFF Determine the nature of the expression of the lacZYA genes, represented by L, and label each genotype as inducible, or no t inducible Symbol Representation r lacl mutant cannot bind to the operator s lacl mutant always binds to the operator o Operator mutant that prevents repressor no "L+, F. binding F the wild-type operator, o*, and laci gee L constiutive constitutive on a plasmid ISO*LF L lacZYA genes Ext .0 Previous Give Up & View Solution O Check Answer 0 Next

Explanation / Answer

I+o+ L+ - Inducible  

- When lactose is present, allolactose binds to the lac repressor, causing an allosteric change in its shape.

- In its changed state, the lac repressor is unable to bind tightly to its cognate operator.

- This effect is referred to as induction, because it induces, rather than represses, expression of the metabolic genes.

I- O+L+- No Transcription

-  lac operon cannot be induced even in the presence of lactose.
- Super-repressor mutations typically located in domain that binds allolactose.
- Usually lac repressor cannot bind to allolactose and therefore remains bound to lac operator site and induction cannot occur.

I+ OC L+ F' - Constitutive -

- Lac Repressor does not inhibit binding of RNA Pol to PLac but transcriptional initiation is blocked.

- This, RNA Pol is "pre-positioned" for transcription when the repressor leaves.

- Understand the basis for the constitutive expression phenotype resulting from the lacI- and lacOc mutations.

- Also understand the basis of the Lac- phenotype resulting from the lacIS mutation.

I- O+ L+ F' - No transcription -

- lac mutant cannot bind to operator.

IS O+ L+ - Constitutive -

- Lac Repressor does not inhibit binding of RNA Pol to PLac but transcriptional initiation is blocked.

- Understand the basis for the constitutive expression phenotype resulting from lacIS mutations.

IS O+ L+ F' - Incucible -

- In wild-type Opretor, a low background level of transcription leads to production of about 50 molecules of - Galactosidase per cell.

- This level may increase 100X after induction.

- lacZ, lacY, lacA are contiguous and transcribed in the given order from the same promoter to create a mRNA.

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