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FUNC BIO CH 18

Terms in this set (29)

Which of the following levels of gene expression allows the most rapid response to
environmental change?
post-translational control
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?
Cells would expend significantly more energy.
Although the expression of most genes is tightly regulated, some genes are expressed at
roughly constant rates. Which of the following genes would you predict to be constitutively
(constantly) expressed?
genes that code for regulatory proteins
The greatest expression of the lac operon occurs when lactose levels are ________.
high and glucose levels are low
Altering patterns of gene expression in prokaryotes would most likely serve an organism's
survival by ________.
allowing an organism to adjust to changes in environmental conditions
Imagine that you have set up a genetic screen to identify E. coli mutants that cannot
metabolize the amino acid tryptophan for energy. 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 ________.
can grow only on the plates with glucose
In the first step of their experiments, Jacob and Monod treated E. coli cells with ultraviolet
light or X-rays to ________.
increase the frequency of mutations in all genes
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. X-gal is likely to be a compound ________.
chemically similar to lactose
An E. coli cell without a functional lacI gene is expected to ________.
always produce β-galactosidase
Which of the following, when taken up by a cell, binds to a repressor so that the repressor no
longer binds to the operator?
inducer
Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is
presented for the first time with the sugar lactose (containing allolactose) as a potential food
source. Which of the following occurs when lactose enters the cell?
Allolactose binds to the repressor protein.
In negative control, a gene is switched off when ________.
a regulatory protein binds to DNA and shuts down transcription
The product of the lacI gene functions most like a car's ________.
parking brake
Suppose several genes are grouped together in a bacterial genome and the group results in a
single enzyme. If one of these genes is mutated and the enzyme is no longer active, this gene
must be part of ________.
an operon
If you wanted to prevent a regulatory protein from changing gene expression, you would
have to prevent physical contact between the protein and ________.
DNA
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 ________.
allosteric regulation of the repressor
According to the lac operon model proposed by Jacob and Monod, what is predicted to occur
if the operator is removed from the operon?
The lac operon would be transcribed continuously.
The product of the lacI gene is ________.
the repressor
Which of the following is a protein produced by a regulatory gene?
repressor
Most repressor proteins are allosteric. Which of the following binds with the repressor to
alter its conformation?
inducer
There is a mutation in the repressor that results in a molecule known as a super-repressor
because it represses the lac operon permanently. Which of these would characterize such a
mutant?
It cannot bind to the inducer.
If she moves the promoter for the lac operon to the region between the beta galactosidase
(lacZ) gene and the permease (lacY) gene, which of the following would be likely?
Beta galactosidase will not be produced.
If she moves the operator to the far end of the operon, past the transacetylase (lacA) gene,
which of the following would likely occur when the cell is exposed to lactose?
The structural genes will be transcribed continuously.
If she moves the repressor gene (lacI), along with its promoter, to a position at some several
thousand base pairs away from its normal position, we would expect the ________.
lac operon will function normally
The arabinose operon (ara) provides a particularly interesting example of ________ in that
when arabinose is present in the environment, the operon is transcribed.
positive control
Under what condition is the AraC protein an activator?
The AraC protein is an activator when it is bound to arabinose.
One interesting and surprising finding regarding the regulation of the ara operon is that it is
under both positive and negative control. What protein is responsible for the dual action of this
operon?
AraC is responsible for both the positive and negative control of the ara operon.
When many genes of an organism are globally regulated, those genes are considered as
regulon genes. What is the common theme of such genetic regulation?
Genes of regulons are silenced by a common repressor.
In what general way are regulons regulated?
Regulons can be under either positive or negative control.
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