Microbiology: An Evolving Science (Fourth Edition)
4th Edition
ISBN: 9780393615098
Author: John W. Foster, Joan L. Slonczewski
Publisher: W. W. Norton & Company
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Chapter 10.2, Problem 2TQ
Summary Introduction
To review:
The effects of null mutations on the induction of beta-galactosidase by lactose, expression of the lacZ gene, and catabolite repression.
Introduction:
The role of lacI (lactose inducer) is to repress the lac operon. It is a tetramer form that binds to the two-lactose operator region (lacO and lacO1). These operator regions cover the lacZYA promoter and are responsible to control the transcription of these structural genes. LacI on binding prevents the RNA (ribonucleic acid) polymerase activity and stops the transcription process.
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Chapter 10 Solutions
Microbiology: An Evolving Science (Fourth Edition)
Ch. 10.1 - Prob. 1TQCh. 10.2 - Prob. 1TQCh. 10.2 - Prob. 2TQCh. 10.2 - Prob. 3TQCh. 10.2 - Prob. 4TQCh. 10.2 - Prob. 5TQCh. 10.3 - Prob. 1TQCh. 10.3 - Prob. 2TQCh. 10.4 - Prob. 1TQCh. 10.5 - Prob. 1TQ
Ch. 10.5 - Prob. 2TQCh. 10.6 - Prob. 1TQCh. 10 - Prob. 1RQCh. 10 - Prob. 2RQCh. 10 - Prob. 3RQCh. 10 - Prob. 4RQCh. 10 - Prob. 5RQCh. 10 - Prob. 6RQCh. 10 - Prob. 7RQCh. 10 - Prob. 8RQCh. 10 - Prob. 9RQCh. 10 - Prob. 10RQCh. 10 - Prob. 11RQCh. 10 - Prob. 12RQCh. 10 - Prob. 13RQCh. 10 - Prob. 14RQCh. 10 - Prob. 1TQCh. 10 - Prob. 2TQCh. 10 - Prob. 3TQCh. 10 - Prob. 4TQ
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- . An interesting mutation in lacI results in repressorswith 110-fold increased binding to both operator andnonoperator DNA. These repressors display a “reverse”induction curve, allowing β-galactosidase synthesis inthe absence of an inducer (IPTG) but partly repressingβ-galactosidase expression in the presence of IPTG. Howcan you explain this? (Note that, when IPTG binds a repressor, it does not completely destroy operator affinity,but rather it reduces affinity 110-fold. Additionally, ascells divide and new operators are generated by thesynthesis of daughter strands, the repressor must findthe new operators by searching along the DNA, rapidlybinding to nonoperator sequences and dissociating fromthem.)arrow_forwardIf the lacl gene is mutated so that the repressor protein no longer binds to lactose, what will be the effect on the expression of B-galactosidase in lactose's presence and absence? Explain. If the promoter for lacl is mutated so that the expression of the repressor increases, what will be the effect on the expression of B-galactosidase in the presence and absence of lactose? Explain. D. (Extremely tricky question!) Describe the behavior of the lac operon assuming that the lacl gene has been mutated so that the repressor now binds to DNA in the presence of lactose but cannot bind to DNA in the absence of lactose.arrow_forwardCTP synthetase catalyzes the glutamine-dependent conversion of UTP to CTP. The enzyme is allosterically inhibited by the product, CTP. Mammalian cells defective in this allosteric inhibition are found to have a complex phenotype: They require thymidine in the growth medium, they have unbalanced nucleotide pools, and they have an elevated spontaneous mutation rate. Explain the likely basis for these observations.arrow_forward
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