To study the lac operon, you engineer a strain of E coli to have a lac operon in which the lac Z gene is replaced by the gene for green fluorescent protein (GFP). Expression of GFP generates a green color in the cells that can be easily quantitated with a fluorescence microscope. You test the activity of the operon in the absence of the inducer IPTG, the presence of the inducer IPTG and the presence of an antibiotic the completely inhibits RNA polymerase (i.e. no gene expression). You then use this

Biochemistry
6th Edition
ISBN:9781305577206
Author:Reginald H. Garrett, Charles M. Grisham
Publisher:Reginald H. Garrett, Charles M. Grisham
Chapter32: The Reception And Transmission Of Extracellular Information
Section: Chapter Questions
Problem 21P
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To study the lac operon, you engineer a strain of E coli to have a lac operon in which the lac Z gene is replaced by the gene for green fluorescent protein (GFP). Expression of GFP generates a green color in the cells that can be easily quantitated with a fluorescence microscope. You test the activity of the operon in the absence of the inducer IPTG, the presence of the inducer IPTG and the presence of an antibiotic the completely inhibits RNA polymerase (i.e. no gene expression). You then use this system to test the effects of various mutation on the activity of the operon. Match the following mutations with the activity (A, B or C) you would expect to observe with the mutation. All experiments are done in the presence of IPTG unless otherwise stated.

100
GFP Fluorescence
B
1
C
(+) IPTG
(+) Antibiotic
✓ Mutation in Lac I that prevents binding of IPTG. A. Activity A
B. Activity B
90
80
70
60
50
30
20
10
GFP Expression
0
A
(-) IPTG
Transcribed Image Text:100 GFP Fluorescence B 1 C (+) IPTG (+) Antibiotic ✓ Mutation in Lac I that prevents binding of IPTG. A. Activity A B. Activity B 90 80 70 60 50 30 20 10 GFP Expression 0 A (-) IPTG
✓ Mutation in Lac I that prevents binding of IPTG. A. Activity A
B. Activity B
C. Activity C
✓Point mutation in lac Y that inhibits its activity.
✓ Deletion of the Shine-Dalgarno (S/D) sequence
prior to lacZ gene
✓ Deletion of lacl gene
✓ lacl gene is moved 6 kb 3' to GFP gene
✓ Add high levels of Tryptophan in the absence of
IPTG
Mutation in operator DNA sequences so that lacl
no longer binds Lacl. Measure in the absence of
IPTG.
Deletion of 1-59 sequence of lacl in the
presence of IPTG
Transcribed Image Text:✓ Mutation in Lac I that prevents binding of IPTG. A. Activity A B. Activity B C. Activity C ✓Point mutation in lac Y that inhibits its activity. ✓ Deletion of the Shine-Dalgarno (S/D) sequence prior to lacZ gene ✓ Deletion of lacl gene ✓ lacl gene is moved 6 kb 3' to GFP gene ✓ Add high levels of Tryptophan in the absence of IPTG Mutation in operator DNA sequences so that lacl no longer binds Lacl. Measure in the absence of IPTG. Deletion of 1-59 sequence of lacl in the presence of IPTG
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