BIOL 1201 Chapter : Topic 10 Gene Regulation

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azuremammoth471

15 Mar 2019

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In a repressible operon is the repressor made in an active or inactive form. When no trp is present the repressor is ____ to the operator and the dna ___ transcribed; not bound, is. When no try is present the repressor is inactive and the dna is transcribed (you need the repressor to be inactive to make genes and thus dna will be transcribed) When trp is present the repressor is active and the dna is not transcribed. When no lactose is present the repressor is active and the dna is not transcribed. When lactose is present the repressor is inactive and the dna is transcribed. In a repressible operon the repressor protein is made in an (inactive form) and (does not) bind to the operator preventing (transcription) Why regulate: energetics (it is expensive to make proteins, control: making the appropriate enzyme, control genes responsible for the protein.

Related Questions

A theoretical operon (amo) in E. coli contains several structural genes encoding enzymes involved in the biosynthesis of a particular amino acid. Unlike the lac operon, in which the repressor gene is separate from the operon itself, for the amo operon, the repressor gene is found within the operon itself. When the end product amino acid is present, it binds to the repressor, and this complex binds to the operator, repressing the operon. In the absence of the amino acid, the repressor fails to bind to the operator, and transcription proceeds. Characterize this operon, comparing it to the regulation of the lac and trp operons. Be sure to discuss how regulation is affected by having the repressor gene as part of the operon.

Then, consider the following mutations:

a) Mutation in the operator region;

b) Mutation in the promoter region;

c) Mutation in the repressor gene.

In each case, state whether the operon will be transcribed or not, and describe how the mutation affects the regulation of the operon. Compare each response to the equivalent situation in the lac and trp operons.

You are analyzing mutants in an Operon in an uncharacterized bacterial species using a method similar to what Jacob and Monod did to analyze the lac operon (see your text book Fig 14.7). This operon is induced in the presence of Sucrose to produce a sucrose metabolizing enzyme, the expression of which can be monitored using a reporter assay. A pink colored product is produced when an artificial substrate is added and the sucrose metabolizing enzyme is present. Like the ONPG assay, this assay is quantitative so the more enzyme, the darker the pink. In this operon, induction by sucrose is mediated by an Activator protein that when bound to its inducer sucrose, is able to bind to Operator A. The operon is also repressible by lactose. Repression by lactose is mediated by a Repressor protein that when bound to its co-repressor lactose, is able to bind to Operator B.

Based on this description, state whether the activator, the repressor, both, or neither would be bound to their respective operators under each set of conditions in wild type bacteria.

No Lactose

No Sucrose

Lactose

No Sucrose

No Lactose Sucrose

Lactose

Sucrose

Wild Type

A series of mutants is described below:

Activator Mutant A â Activator cannot bind to DNA

Activator Mutant B â Activator cannot bind to sucrose

Repressor Mutant A â Repressor cannot bind to DNA

Repressor Mutant B â Repressor cannot bind to lactose

Pink color was measured in wild type bacteria under the listed conditions. Based on the measurements in the wild type condition, state the amount of pink color that would be produced.

	-Lactose -Sucrose	+Lactose -Sucrose	-Lactose +Sucrose	+Lactose +Sucrose
Wild Type	0.030	0.030	1.891	0.124
Activator Mutant A
Activator Mutant B
Repressor Mutant A
Repressor Mutant B

emeraldspider356

1. The lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. The operon system is inducible in that it can be âturned onâ by the presence of lactose. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products.

These mutations include:

I ^- = produces a repressor protein that can not bind to the operator region

I ^s = produces a repressor protein that can not be removed from the operator region

O ^C = can not bind a repressor protein

Z ^- = produces a defective (non-functioning) Î²-galactosidase enzyme

( I^- are recessive to I⁺; I⁺ recessive to I^S )

Detail the functionality of the lac

operon under the following genetic and cellular conditions.

GENES	Lactose present	Repressed (yes/no)	Constitutive (yes/no)	Inducible (yes/no)
I + O + Z +	no
I + O C Z +	no
I S O + Z +	yes
I - O + Z +	yes
I S O C Z +	no

sangriadolphin65

BIOL 1201 Chapter : Topic 10 Gene Regulation

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