IBIO 341 Lecture Notes - Lecture 34: Lac Operon, Operon, Repressor

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harlequinsalmon729

28 Jun 2019

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Regulator: composed of the gene that codes for the repressor, a protein capable of repressing the operon. Operator: acts as an on/off switch for transcription. Structural locus: made up of three genes, each coding for a different enzyme needed to catabolize lactose. Binding sites for the operator sequence on the dna and lactose. In the absence of lactose, the repressor binds to the operator, blocking transcription of structural genes. The regulator gene lies upstream of the operator and is transcribed constitutively. Repressible operons are usually in the on mode. Will only be turned off when the nutrient is no longer required. Excess nutrient serves as a corepressor to block the action of the operon. The result of bacteria turning on or off a complement of genes that leads to phenotypic changes. Involves turning on genes mediated by regulatory proteins, as described with operons. An event in which one bacterium donates dna to another bacterium.

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

For this question, focus on four parts:

I, the gene that produces the repressor protein;

P, the promoter region where RNA polymerase binds to initiate transcription;

O, the Operator site, where the repressor binds. When the repressor binds, it prevents transcription; and

ZYA, the three structural genes, all of which are required for the successful utilization of lactose as a food source.

In the left column of the table below, we indicate the genetic composition at the lac operon of particular strains of E. coli cells. A "+" (plus sign) following the letter indicates the wild-type allele (or normally functioning version of the gene). For I, P, and ZYA, a "-" (negative sign) following the letter indicates the mutant allele (or non-functional version of the gene). For the O allele, a "C" indicates the mutant or constitutive allele. It is not functional in that the repressor cannot bind, but it is functional in that transcription can still occur.

Given the conditions stated in each column, please indicate for each genotype whether lac mRNA is produced and at what level by typing in one of the following words in each cell in the table:

"Abundant"

"Minimal"

"None"

The completely wild-type genotype has already been filled in.

	Cellular conditions:
Genotype	Glucose present (low cAMP) and no lactose	Glucose present (low cAMP) and lactose present	No glucose (high cAMP) and lactose present
*I⁺ P⁺ O⁺ ZYA⁺*	None	Minimal	Abundant
*I^- P⁺ O⁺ ZYA⁺*
*I⁺ P^- O⁺ ZYA⁺*
*I⁺ P⁺ O^c ZYA⁺*
*I⁺ P⁺ O⁺ ZYA^-*

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IBIO 341 Lecture Notes - Lecture 34: Lac Operon, Operon, Repressor

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