BIO-0013 Lecture Notes - Lecture 20: Lac Repressor, Lac Operon, Repressor

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maroonkoala256

29 Nov 2016

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Binds operator(downstream of promoter) sequence and blocks transcription: jacob and monod identified a mutant that suggested that a repressor regulated lac operon. Identified a mutant e. coli where lacz and lacy were always expressed under all conditions (glucose only or glucose and lactose or lactose only) Binds operator (downstream of promoter) dna sequence and blocks transcription: normal laci gene, repressor is constitutively synthesized, always made. Lactose acts as inducer of lac operon transcription: how do things change in the presence of glucose, glucose inhibits galactoside permease and thereby blocks entrance of lactose (the inducer, regulating gene expression in eukaryotes, nucleus. Inheritance not due to dna sequence: experimental question: can environmental conditions of mother lead to epigenetic consequences in offspring (children), rats fed a low-protein diet give birth to more type 2 diabetic mice. Even when progeny were fed a normal diet: diabetic mice have decreased hnf4a expression (transcription factor (tf) important controlling other genes involved in glucose regulation)

Related Questions

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^-*

champagneyak301

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?

BIO-0013 Lecture Notes - Lecture 20: Lac Repressor, Lac Operon, Repressor

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