Operons Continued
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Rodermel/Dr. Tuggle
11/29/14
1. The mmm operon, which has sequences A, B, C and D encodes enzymes 1 and 2.
Mutations in sequences A, B, C, and D have the following effects.
Mmm Absent
Enzyme 1
Enzyme 2
+
+
+
+
+
+
-
No mutation
A
B
C
D
Mmm Present
Enzyme 1
Enzyme 2
+
+
+
-
a. Is the mmm operon inducible or repressible?
b. Indicate which sequence is part of the following components of the operon.
a. Regulator gene __________
b. Promoter ____________
c. Structural gene for enzyme 1 ________
d. Structural gene for enzyme 2 ________
2. A mutation at the operator site 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.
3. For each of the following types of transcriptional control, indicate whether the protein
produced by the regulator gene will be synthesized initially as an active repressor,
inactive repressor, active activator, or inactive activator.
a. Negative repressible
b. Positive repressible
c. Negative inducible
d. Negative inducible
4. For each of the following, describe the production of B- galactosidase and permease with
a (+) or (-) for both lactose present and lactose absent conditions.
a. lacI+ lacP- lacO+ lacZ- lacY+ / lacI- lacP+ lacO+ lacZ+ lacYb. lacI+ lacP- lacOC lacZ+ lacY+
c. lacI+ lacP- lacOC lacZ- lacY+ / lacI- lacP+ lacO+ lacZ+ lacYLactose Absent
B-galactosidase Permease
Lactose Present
B-galactosidase Permease
a.
b.
c.
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu
5. LacI+ is (dominant/recessive) to LacI-. This is because LacI acts (cis/trans).
6. Explain why mutations in the lacO gene are cis in their effects.
7. Describe the three different types of mutations that are possible in structural genes.
8. Describe catabolite repression and how it relates to the lac operon in E. coli.
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu