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[001-072] PIERCE STUDENT MAN
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The Control of
Gene Expression
**1. A mutation occurs at the operator site that prevents the regulator protein from binding. What
effect will this mutation have in the following types of operons?
a. Regulator protein is a repressor in a repressible operon.
b. Regulator protein is a repressor in an inducible operon.
**2. The blob operon produces enzymes that convert compound A to compound B. The operon is controlled by a regulatory gene S. Normally the enzymes are synthesized only in the absence of compound
B. If gene S is mutated, the enzymes are synthesized in the presence and in the absence of compound B.
Does gene S produce a repressor or an activator? Is this operon inducible or repressible?
*3. A mutation causes excess levels of cAMP. What will be the effect of this mutation on transcription
of the lac operon?
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Pierce, Genetics: A Conceptual Approach
[001-072] PIERCE STUDENT MAN
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Pierce, Genetics: A Conceptual Approach
Chapter 16 The Control of Gene Expression
**4. For E. coli strains with the lac genotypes given below, use a plus (+) to indicate the synthesis of βgalactosidase and permease or a minus (−) to indicate no synthesis of the enzymes.
Lactose absent
b-galactosidase
Genotype of strain
1
2
3
4
5
6
7
8
9
10
11
12
+
+
+
+
Permease
Lactose present
b-galactosidase
Permease
+
lacI lacP lacO lacZ lacY
lacI–lacP+lacO+lacZ+lacY+
lacI+lacP+lacOclacZ+lacY+
lacI−lacP+lacO+lacZ+lacY−
lacI−lacP−lacO+lacZ+lacY+
lacI+lacP+lacO+lacZ−lacY+/
lacI−lacP+lacO+lacZ+lacY−
lacI−lacP+lacOclacZ+lacY+/
lacI+lacP+lacO+lacZ−lacY−
lacI−lacP+lacO+lacZ+lacY−/
lacI+lacP−lacO+lacZ−lacY+
lacI+lacP−lacOclacZ−lacY+/
lacI−lacP+lacO+lacZ+lacY−
lacI+lacP+lacO+lacZ+lacY+/
lacI+lacP+lacO+lacZ+lacY+
lacIslacP+lacO+lacZ+lacY−/
lacI+lacP+lacO+lacZ−lacY+
lacIslacP−lacO+lacZ+lacY+/
lacI+lacP+lacO+lacZ−lacY+
***5. Give all possible genotypes of a lac operon that produces β-galactosidase and permease under the
following conditions. Do not give partial diploid genotypes.
Lactose absent
Lactose present
b-galactosidase
Permease
b-galactosidase
permease
a
–
–
+
+
b
–
–
–
+
c
–
–
+
–
d
+
+
+
+
e
–
–
–
–
f
+
–
+
–
g
–
+
–
+
Genotype
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[001-072] PIERCE STUDENT MAN
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Pierce, Genetics: A Conceptual Approach
Chapter 16 The Control of Gene Expression
**6. The dod operon, which has sequences A, B, C, and D, encodes enzymes 1 and 2. Mutations in
sequences A, B, C, and D have the effects shown below, where (+) = enzyme synthesized, (−) = enzyme
not synthesized.
dod absent
Mutation in sequence
dod present
Enzyme 1
Enzyme 2
Enzyme 1
Enzyme 2
No mutation
−
−
+
+
D
−
−
−
+
A
−
−
−
−
C
−
−
+
−
B
+
+
+
+
a. Is the dod operon inducible or repressible?
b. Indicate which sequence (A, B, C, or D) is part of the following components of the operon.
_____Regulator gene
_____Promoter
_____Structural gene for enzyme 1
_____Structural gene for enzyme 2
**7. Listed below are some mutations that have been found in the 5' UTR region of the trp operon
of E. coli. What would be the most likely effect of these mutations on transcription of the trp structural genes?
a. A mutation that prevents the binding of the ribosome to the 5' end of the mRNA 5' UTR.
b. A mutation that changes the tryptophan codons in region 1 of the mRNA 5' UTR to codons for alanine.
c. A mutation that creates a stop codon early in region 1 of the mRNA 5' UTR.
d. Deletions in region 2 of the mRNA 5' UTR.
e. Deletions in region 3 of the mRNA 5' UTR.
f. Deletions in region 4 of the mRNA 5' UTR.
g. Deletion of the string of adenine nucleotides that follows region 4 in the 5' UTR.
*8. Gene control through attenuation is only found in prokaryotic cells. Why would this process not
work in eukaryotic cells? Explain your answer.
*9. What would be the effect of a mutation that destroyed the ability of poly(A) binding protein
(PABP) to attach to a poly(A) tail?
**10. A common feature of many eukaryotic mRNAs is the presence of a rather long 3' UTR, which
often contains consensus sequences. Creatine kinase B (CK-B) is an enzyme important in cellular
metabolism. Certain cells—termed U937D cells—have lots of CK-B mRNA, but no CK-B enzyme is
present. In these cells, the 5' end of the CK-B mRNA is bound to ribosomes, but the mRNA is apparently not translated. Something inhibits translation of the CK-B mRNA in these cells.
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