01:119:115 Lecture Notes - Lecture 16: Interphase, Allolactose, Galactose

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olivebee315

21 Apr 2016

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Introduction: gene regulation (not energetically favorable to keep all genes on at all times) Facultative genes - genes that have very regulated transcription and translation. Constitutive genes - genes that have constant strain of transcription and translation: lac operon in bacteria. Lactose metabolism demonstrate gene regulation in e. coli: coli - has ability to adjust to chemical environment changes, coli needs to be able to digest lactose (needs regulation) Operon - genetic structure found only in prokaryotes: structural genes with related function (lac operon) Promoter - rna polymerase binding site, not transcribed. Operator - on/off switch for gene expression, not transcribed. Beta galactosidase - hydrolyze lactose into glucose + galactose. Structure must be all on or all off: lactose expression. If lactose is present, rapid increase in expression: repressor genes - not part of operon; codes for repressor protein; constitutive repressor bc lactose is not always present.

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

18) In your research on gene regulation in E. coli, you produce 2 mutant strains with the same phenotype: they can grow on lactose but not on glucose. To investigate these 2 mutants further, you perform a complementation test using them and discover that the diploid combination strain can grow on glucose or lactose. From this, you can deduce that:

a.)Both mutants have a mutation in the same gene

b.)The 2 mutants have mutations in different genes
c.)Glucose and lactose metabolic pathways in E. coli utilize at least one shared gene in common
d.)At least 2 different genes are required for glucose metabolism in E. coli
e.) b) and d)

19. In your research on the lac operon, you produce a unique regulatory mutatant strain of E. Coli where the lac l gene's repressor protein binding site for the operator is normal (wild-type) but its lactose binding site no longer binds lactose. The expected phenotype of this mutant will be:

a. inability to grow on lactose only medium

b. ability to grow on lactose only medium

c. blue colony color when grown on glycerol plus x-gal medium

d. blue colony oclor when grown on lactose plus x-gal medium

e. b & d

20.

20) In your research on the lac operon, you create a diploid E.coli strain with the following genotype (+) = wild type gene, (-) = mutant gene.

I- /O+ /Z- /Y+

I+ /Oc /Z+ /Y+
Can this diploid mutant grow on medium containing lactose as the only carbon source?

a) Yes

b) No

c) Maybe, it depends on if the Oc mutation is dominant or recessive

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01:119:115 Lecture Notes - Lecture 16: Interphase, Allolactose, Galactose

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