Download LAC OPERON ACTIVITY - Fairview High School

TRYP and LAC OPERON SIMULATION
Name: ___________________________________________ Period: ____
Scoring: Part 1: ____ / 2 drawings
+
____/ 3 Questions = ______/ 5
Part 2: _____ / 3 drawings
+
____/ 6 Questions = ______/ 9
Quiz: _____/ 14
Total: _____/ 28
Part 1: TRYP OPERON SIMULATION LAB
1)[ tryp] = high => gene activity (low or high)
Promoter
Operator
Repressor Binding Site
Tryp E
gene
Tryp D
gene
2)[tryp] = low => gene activity (low or high)
Tryp C
gene
Part 1 QUESTIONS:
1) Why is the tryp operator described as repressible?
2) For repressible operons, is the gene activity changed in response to the presence of the
precursor in the pathway or the final product metabolite in the pathway?
3) How does a repressor prevent transcription?
Part 2: LAC OPERON SIMULATION DRAWINGS
QUESTION # 1: Circle the correct choice: If [Glucose] = high, then [cAMP] = high
or low
Conditions to simulate:
1) [Glucose] = high, [lactose] = low
PROMOTER
Operator
CRP or CAP Site
lacZ gene
lacY gene
lacA gene
2) [Glucose] = high, [lactose] = high
PROMOTER
CRP or CAP Site
Operator
lacZ gene
lacY gene
lacA gene
3) [Glucose] = low, [lactose] = high
PROMOTER
Operator
CRP or CAP Site
lacZ gene
lacY gene
lacA gene
Part 2 Questions to answer:
2) Is the lactose the precursor or the final product of the metabolic pathway for the lac
genes?
3) Why is the lac operon described as inducible?
4) Describe how a high [cAMP] activates transcription.
5) Given the following pathway
X -> Y -> Z,
A) If [X] primarily turns the gene on and off, the pathway is most likely to be
(inducible or repressible)
B) If [Z] primarily turns the gene on and off, the pathway is most likely to be
(inducible or repressible)
Extension: Genetic Studies of the Lac Operon – BE SURE TO READ
BACKGROUND INFORMATION IN LAB MANUAL FIRST! Discuss the data with
your lab team but make sure your final answers are your own individual. This question is
not a part of operon lab quiz)
EXPLANATION OF CLASS I MUTANTS:
1) Below is a diagram of the lac operon model proposed by Jacob and Monot. Note: I gene
codes for repressor protein. Genes Z, Y and A code for proteins directly involved in bringing
lactose into the cell and breaking it down. (Note: Z is the gene for beta-galactosidase; recall that
the activity of this enzyme is used to monitor operon expression.)
A) There are three possible regions of DNA mutation:
1) The I gene that codes for repressor protein.
2) The operator region
3) The lactose metabolism genes (Z,Y,A)
Based on the data from Table 2 which one of these regions can be immediately eliminated
and why?
B) On the diagram below, CIRCLE the location of the mutation.
Mutated Lac Operon on Chromosome
I gene
Operator
Z gene
Y gene
A gene
Proteins for Lac Digestion,
including beta-galactosidase
Repressor Protein
Wild Type copy Lac Operon on
Plasmid
I gene
Operator
Z gene
Y gene
A gene
Repressor Protein
C) Using symbolic pictures for repressor protein and/or notations on the diagram as well as
words explain how the mutation you propose is consistent with the experimental data.
EXPLANATION OF CLASS II MUTANTS:
2) Below is a diagram of the lac operon model proposed by Jacob and Monot. Note: I gene
codes for repressor protein. Genes Z, Y and A code for proteins directly involved in bringing
lactose into the cell and breaking it down. (Note: Z is the gene for beta-galactosidase; recall that
the activity of this enzyme is used to monitor operon expression.)
A) There are three possible regions of DNA mutation:
1) The I gene that codes for repressor protein.
2) The operator region
3) The lactose metabolism genes (Z,Y,A)
Based on the data from Table 2 which one of these regions can be immediately eliminated
and why?
B) On the diagram below, CIRCLE the location of the mutation.
Mutated Lac Operon on Chromosome
I gene
Operator
Z gene
Y gene
A gene
Proteins for Lac Digestion,
including beta-galactosidase
Repressor Protein
Wild Type copy Lac Operon on
Plasmid
I gene
Operator
Z gene
Y gene
A gene
Repressor Protein
C) Using symbolic pictures for repressor protein and/or notations on the diagram as well as
words explain how the mutation you propose is consistent with the experimental data.