BIO 1140 Lecture 15: BIO 1140 Lecture 15

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olivefox459

24 Aug 2016

School

University of Ottawa

Department

Biology

Course

BIO 1140

Professor

Caroline Petit- Turcotte

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Document Summary

Prokaryotes regulate using operons, region or areas that allow different on and off switches. Lac repressor represses operon and depends on the concentration of lactose present in the environment. Controls whether transcription will be able to happen or not. Coding regions usually have more than one gene. All are under control of the same promoter. Adding a region called an operator which adds an additional on/off switch. Repressor can go and bind to operator and stops transcription by not allowing the polymerase to move forward. When there"s lactose available, it will stop the repressor from binding to the operator. No lactose your repressor gene is active. Repressor binds to operator and acts like a clamp meaning genes will not be transcribed. B-galactosidase changes lactose to allolactose so that it is unable to bind to the repressor. The product of the transcription of an operon is one set of related mrnas that code for functionally related proteins.

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.

1.) What type of control best describes the lac operon when it is regulated by allolactose? Explain the features of this type of regulation using the lac operon as an example.

2.) What is positive gene regulation?

a) when an activator protein binds to the operator of a gene to turn expression off

b) when a repressor protein binds to the operator of a gene to turn expression off

c) when an activator protein binds to the operator of a gene to turn expression on

d) when a repressor protein binds to the operator of a gene to turn expression on

e) when a protein binds to DNA to change gene expression

3.) In the lactose operon of E. coli, what is the function of each of the following genes or sites: a) regulator, b) operator, c) promoter, d) structural gene Z and e) structural gene Y?

a) regulator gene

b) operator

c) promoter

d) structural gene Z

e) structural gene Y

4.) In a negative, repressible regulatory mechanism, transcription of the structural gene(s) occurs in

a) the presence of the co-repressor, but not in its absence.

b) the absence of the co-repressor, but not in its presence.

c) the presence of the inducer, but not in its absence.

d) the absence of the inducer but not in its presence.

e) the absence or presence of the co-repressor.

What are answers and can you explain them to me?

In E.coli the lac operon is controlled by the presence or absence of both lactose and glucose. The lac repressor only allows expression in the presence of lactose, and it is also only activated when glucose levels are low, such that the lac operon is on when lactose is present but glucose is not.

You have cells that are mutant in the gene coding for the Lac repressor (I-). These cells lack the Lac repressor under all conditions. For these mutant cells, state whether the Lac operon will be switched on or off in the following situations, whether the lac repressor (I) is bound to the operator, and whether CAP-cAMP is bound upstream of the promoter.

a. in the presence of glucose and lactose

b. in the presence of glucose and the absence of lactose

c. in the absence of glucose and the absence of lactose

d. in the absence of glucose and the presence of lactose

BIO 1140 Lecture 15: BIO 1140 Lecture 15

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