BIO 1140 Lecture Notes - Lecture 8: Transposable Element, Microrna, Dicer

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sapphirecod902

18 May 2016

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In prokaryotes, the expression of genes is regulated mainly by operons. They have 4, sometimes more genes in a group together and all under the control of the same promoter (no intergenic region). The sections and sequences are one after the other. They"re under the control of the promoter- promoter is where we recruit the rna pol so it reads the coding region. The lac operon is an example of an inducible system of gene expression. Only when the right catalyst is added to the system, in this case the sugar lactose, is the process activated, allowing the genes in question to be expressed. In an operon, we"re gonna add an additional layer of control- an on/off switch- an operator. The operator finds itself between the promoter and the coding region (one spot on the gene). The operator is the one spot on the gene. whereas the operon consists of the promoter, operator, and genes that are under control.

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?

1. The lac operon of E. coli controls the expression of genes that code for enzymes involved in lactose metabolism. The operon system is inducible in that it can be âturned onâ by the presence of lactose. Mutations to various regions of the lac operon have been discovered which affect both the control of gene expression and the function of the gene products.

These mutations include:

I ^- = produces a repressor protein that can not bind to the operator region

I ^s = produces a repressor protein that can not be removed from the operator region

O ^C = can not bind a repressor protein

Z ^- = produces a defective (non-functioning) Î²-galactosidase enzyme

( I^- are recessive to I⁺; I⁺ recessive to I^S )

Detail the functionality of the lac

operon under the following genetic and cellular conditions.

GENES	Lactose present	Repressed (yes/no)	Constitutive (yes/no)	Inducible (yes/no)
I + O + Z +	no
I + O C Z +	no
I S O + Z +	yes
I - O + Z +	yes
I S O C Z +	no

sangriadolphin65

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

BIO 1140 Lecture Notes - Lecture 8: Transposable Element, Microrna, Dicer

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