1 What type of control best describes the lac operon when it

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?

Solution

Question number 1 : Lactose operon is an example of inducible operons. An operon system in which the transcription of the particular mRNA is switched on in reponse to the presence of molecule called inducer. These operons are usually operates in catabolic pathways. So an inducer turns on the transcription of particular genes responsible for their catabolism.

Example: Lactose operon. In lactose operon, lactose( More particulraly allolactose) acts an inducer which turns on the transcription of structural genes required for its catabolism by preventing the binding of repressor protein to the operator site on lac operon.

Lac operon consists of Regulatory sequences and structural gens

Regulatory sequences includes are those in which the RNA polymerase binds and brings about transcription

Reglatory gene: Which codes for a respressor protein

Operator sequence: To which repressor protein binds and prevents the binding of RNA polymerase to promoter sequence because of steric hindrance and stops transcription when lactose is absent and

Structural genes includes

Lac Z: -Galactosidase, An intracellular enzyme that cleaves the disaccaharide lactose into glucose and galactose (Allolactose)

Lac Y: Lactose permease, an inner membrane bound symporter that pumps lactose into the cell using a proton gradient.

Lac A: Thiogalactoside transcetylase, an enzyme that transfers an acetyl group from acetyl-CoA to beta-galactosides