BIO206H5 Lecture Notes - Lecture 17: Adenylyl Cyclase, Recognition Sequence, Hydrogen Bond

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19 Nov 2016

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Bio206 lecture 17 regulation of prokaryote gene expression. Sugar catabolism in e. coli the lac operon. E. coli prefers glucose as an energy and carbon source in absence of glucose, it will use lactose (a disaccharide) but not in the presence of glucose. Many things can be used as a sugar source but e. coli prefers glucose the most. A small metabolite molecule is present in the cytoplasm and is bound to the repressor protein which is also bound to dna, the small repressor protein can. Change the architecture of the protein, causing it to be released by the dna some transcription of the dna can occur. Positive regulation binding of rna polymerase is enhanced and sped up so that in the presence of a protein (called an activator protein) facilitates the binding of rnap (sigma factor present) and transcription can begin very rapidly.

Related Questions

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 the following points, I have summarized Lac operon in Ecoli. I need to check if this is on the right track? and where does 'cleavage of disaccharides' fit into this picture?

Lactose is a disaccharide and the bacteria need specific genes to manage catabolism

1) The lacl promotor gene synthesis the repressor protein which binds to the operator gene stopping the RNA polymerase from coding the lac operon genes

2)But when lactose is present, it needs the specific genes to catabolise lactose

3) So, When allolactose (a derivative of lactose)is present, it binds to the repressor protein, the repressor releases from the operator gene

4) This allows the RNA polymerase can attach to the DNA control region

5) And drive down the operon for transcription and induction of the enzyme lacZ(beta-galactosidase) lacY and lacA which breaks lactose down into glucose and galactose

6) When the lactose is all gone, the repressor returns to the operator in a feedback loop system

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

BIO206H5 Lecture Notes - Lecture 17: Adenylyl Cyclase, Recognition Sequence, Hydrogen Bond

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