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Exam 17: Control of Gene Expression in Bacteria

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Question 1

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Imagine that you've set up a genetic screen to identify E.coli mutants that cannot metabolize the amino acid tryptophan.Beginning with a master plate containing many colonies,you prepare replica plates on medium with glucose or tryptophan as the only energy source.You would look for colonies that _____.

A) cannot grow on either type of media
B) can grow on both types of media
C) can grow only on the plates with tryptophan
D) can grow only on the plates with glucose

E) A) and D)
F) C) and D)

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Question 2

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In negative control of transcription,a gene is activated when _____.

A) a kinase adds a phosphate to DNA
B) lactose is transported into the cell
C) a regulatory protein binds to DNA
D) a regulatory protein is removed from DNA

E) A) and C)
F) A) and B)

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Question 3

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Imagine that you discover a bacterial operon involved in the synthesis of vitamin B₁₂.This operon is regulated by a repressor protein that binds to an operator sequence.Vitamin B₁₂ is the allosteric effector of the repressor-the molecule that binds to the repressor to affect its activity.Predict how vitamin B₁₂ will influence repressor activity.

Use the following information when answering the corresponding question(s) . The lac operon is used in countless ways for genetics research and biotechnology.One important use of the lac operon is to regulate the expression of cloned genes.In this application,some regulatory elements of the operon are fused to the cloned gene that is to be regulated.One application of such technology was reported by Cronin et al. ,The lac operator-repressor system is functional in the mouse,Genes and Development 15 (2001) :1506-17.These investigators fused a portion of the lac operon to the mouse tyrosinase gene,a gene required for pigment production.This recombinant DNA,composed of E.coli lac operon sequences and the mouse tyrosinase gene,was introduced into albino mice using techniques that will be described in Chapter 19.Using the lac operon regulatory sequences,the investigators were able to regulate tyrosinase gene expression.In fact,they were able to convert albino (white) mice into brown mice.The following questions ask you to use your knowledge of the lac operon to deduce how Cronin et al.were able to regulate tyrosinase gene expression in mice. -Refer to the paragraph about the lac operon experiment by Cronin et al.Controlling the production of a pigment is interesting,but in itself seems more a stunt than a valuable research endeavor.What is the broader significance of the results of Cronin et al.?

Use the following information when answering the corresponding question(s) . The lac operon is used in countless ways for genetics research and biotechnology.One important use of the lac operon is to regulate the expression of cloned genes.In this application,some regulatory elements of the operon are fused to the cloned gene that is to be regulated.One application of such technology was reported by Cronin et al. ,The lac operator-repressor system is functional in the mouse,Genes and Development 15 (2001) :1506-17.These investigators fused a portion of the lac operon to the mouse tyrosinase gene,a gene required for pigment production.This recombinant DNA,composed of E.coli lac operon sequences and the mouse tyrosinase gene,was introduced into albino mice using techniques that will be described in Chapter 19.Using the lac operon regulatory sequences,the investigators were able to regulate tyrosinase gene expression.In fact,they were able to convert albino (white) mice into brown mice.The following questions ask you to use your knowledge of the lac operon to deduce how Cronin et al.were able to regulate tyrosinase gene expression in mice. -Refer to the paragraph about the lac operon experiment by Cronin et al.How did Cronin et al.activate expression of tyrosinase to change the color of a white (albino) mouse to brown?

E.coli adenylyl cyclase is most active when _____.

Although the expression of most genes is tightly regulated,some genes are expressed at roughly constant rates (i.e. ,constitutively) .Which of the following genes would you predict to be constitutively expressed?

A compound known as X-Gal is widely used in molecular genetic research.When wild-type (normal) E.coli is grown on medium containing X-Gal,the bacterial colonies turn blue.In contrast,when lacZ mutants are grown on medium containing X-Gal,the bacterial colonies remain their normal white color.What is X-Gal likely to be?

Suppose several genes are grouped together in a genome and the group results in a single enzyme.If one of these genes is mutated and the enzyme is no longer produced,this gene must be part of _____.

Jacob and Monod were intellectually primed to draw the conclusions they did concerning regulation of the lac operon.In part,this was due to their fascination with mechanisms of enzyme regulation.They knew that the activity of some enzymes is regulated when their reaction product binds to the enzyme,changing its shape and therefore its activity.This knowledge allowed them to easily make the intellectual leap to propose _____.

If a scientist wanted to prevent a regulatory protein from changing gene expression,he must prevent physical contact between the protein and _____.

According to the lac operon model proposed by Jacob and Monod,what is predicted to occur if the operator is removed from the operon?

In the first step of their experiments,Jacob and Monod treated E.coli cells with UV light or X-rays in order to _____.

Which of the following is associated with negative control of the lac operon?

Extracellular glucose inhibits transcription of the lac operon by _____.

The product of the lacI gene is most like a car's _____.

How does the inducer change the repressor's affinity for DNA?

The product of the lacI gene is _____.

Bacterial and eukaryotic cells primarily control gene expression at the level of transcription.If instead cells exerted control of gene expression primarily at the post-translational level,what would be different?

The trp repressor blocks transcription of the trp operon when the repressor _____.