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Ch. 18 Study Guide Questions and and answers (1).
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Ch. 18 Study GuideReplica plating is used to isolate mutants that:
A. can produce an enzyme
B. cannot grow in a particular condition
✅✅-B
C. can utilize lactose
D. turn yellow when lactose is broken down -
Why are the genes involved in lactose metabolism considered to be an operon?
A. They occupy adjacent actions on the E. coli chromosome
B. They have a similar function
✅✅
C. they are all required for normal cell function
D. They are all controlled by the same promoter. - -D
In the lac operon, the repressor inhibits transcription when:
A. the repressor is bound to the inducer
B. the repressor is not bound to the inducer
✅✅
C. the repressor is bound to glucose
D. the repressor is not bound to the operator - -B
✅✅
Activators bind to regulatory sequences in _____ and to ______ polymerase. -
-DNA, RNA
✅✅
How does inducer exclusion control gene expression in the lac operon? -
-When glucose and another sugar are present in the environment, inducer
exclusion prevents the use of the other sugar and allows only use of glucose.
A regulon is a set of genes controlled by:
A. one type of regulator of transcription
B. two or more different alternative sigma proteins
✅✅
C. many different types of promoters
D. glucose - -A
E. coli expresses genes for glycolytic enzyme constitutively. Why? -✅✅ -The
glycolytic enzymes are always needed in the cell because they are required to
produce ATP, and ATP is always needed.
✅✅
Explain the difference between positive and negative control over transcription -
-Positive control means that a regulatory protein, when present, causes
transcription to increase. Negative control means that a regulatory protein, when
present, prevents transcription
, Predict what would happen if the lac repressor protein were altered so it could not
bind inducer:
A. The repressor could not bind to DNA
B. The repressor would always be bound to DNA
C. The repressor could bind to DNA only when cells were grown with glucose
✅✅
D. The repressor could bind to DNA only when cells were grown without glucose. -
-B
✅✅
Predict what would happen to regulations of the lac operon if the lacI gene were
moved 50,000 nucleotides upstreams of its normal location. - -Regulation of
the lac operon should be normal. The location of the lacI gene isn't important,
because the gene produces a pertain that diffuses within the cell to there operator.
If any of the following hypothetical drugs could be developed, which would be most
effective in preventing cholera?
A. a drug that increased the amount of the ToxR activator
B. a drug that blocked the DNA-binding activity of the activator
✅✅
C. a drug that increased rates of transcriptions in V. cholerae
D. a drug that increased rates of translation in V. cholerae - -B, since the
activator needs to bind to regulatory sequences to activate gene expression,
preventing DNA binding would cripple the region and prevent cholera.
IPTG is a molecule with a structure very similar to lactose. IPTG can be transported
into cells by galactoside permeate and can bind to the lac repressor protein.
However, unlike lactose, IPTG is not broken down by β-galactosidase. Predict what
✅✅
would occur regarding lac operon regulation if IPTG were added to E. coli growth
medium containing arabinose and no glucose or lactose. - -The lac operon
would be strongly indued. Once inside the cell, the IPTG will bind to the repressor,
causing it to release from DNA. IPTG cannot be broken down, so its concentration
will remain high. Finally, since glucose is absent, there will be no inducer exclusion to
inhibit IPTG transport through the galactoside permeate transporter.
You are interested in using bacteria to metabolize wastes at an old chemical plant
and convert them into harmless compounds. You find bacteria that are able to
tolerate high levels of the toxic compounds toluene and benzene, and you suspect
that this is because the bacteria can break down these compounds into less-toxic
products. If that is true, these toluene- and benzene-hesitant strains will be valuable
✅✅
for cleaning up toxic sites. How could you find out whether these bacteria are
metabolizing toluene as a source of carbon compounds? - -Set up cultures with
individuals that all come from the same colony of toluene-tolerating bacteria. Half the
cultures should have toluene as the only source of carbon; half should have glucose
or another common source of carbon. The glucose-containing medium serves as a
control to ensure that cells can be grown in the lab. Cells will grow in both cultures if
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