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Ch. 18 - Control of Gene Expression in Bacteria
All textbooksFreeman 8th EditionCh. 18 - Control of Gene Expression in BacteriaProblem 7
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Chapter 17, Problem 7

Explain why it makes sense for the lexA regulatory gene of the SOS regulon to be expressed constitutively.

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Hi everyone. Welcome back. Here's our next question. How does S. O. S. Regular help the bacteria during DNA damage? Here's an example of question where it's really important to kind of look over our answers before we kind of zoom in on one. So we've got choi se it produces enzymes that repair the damaged region. Choice be. It cuts out the damaged DNA segment and replaces it with a new sequence choice. See it stops DNA replication and induces DNA repair and neurogenesis. Or D. It kills the cells through apoptosis. Well right away we can eliminate choice D um apoptosis, programmed cell death is the response in multicellular organisms When things go awry and DNA is damaged and multicellular organisms, these cells have to work together and the consequences can be pretty catastrophic. Um when you have the DNA errors. So if it's enough the cell will essentially kill itself through apoptosis with bacteria with single cell organisms. There's a little more leeway there for repairing DNA damage and in fact some of the damage isn't repaired in a very accurate way which allows some mutations to arise that might be beneficial. So it's a little confusing because Choice A. And Choice be both involved DNA repair which is definitely part of the process of the S. O. S. Regular but it's not the complete answer. So the S. O. S. Regular phone. It caused the expression of over 50 different genes and it starts by stopping DNA replication. When an error occurs kind of halting that cell cycle then it will have you stimulate the production of enzymes that replace single base pairs, so production of enzymes that repair single bases if there's still significant damage if it goes on to produce more enzymes that replaced the damaged DNA with random bases. This actually induces um mutation in the bacteria but this allows the bacteria to adapt very quickly to situations. So this can actually be advantageous. Even though this unfaithful repair seems like it would be a disadvantage. So, Choice A. And Choice B. Are not really the uh compared to Choice C. Are not really a good enough description of what's going on. So Choice C, which says it stops DNA replication and induces DNA repair. And neurogenesis is the answer we want because that describes all three of these functions, stopping replication inducing repair and then causing this mutations based on replacing damaged bases with random DNA base pair is not the correct ones. Um Is that the most thorough description of how the S. O. S. Regularly helps bacteria? It choices A and B. Are not a full description of all the ways in which it acts. So that's why they are not are correct answers. Hope this helps you in the next video
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Related Practice
Textbook Question

A regulon is a set of genes controlled by a. one type of regulator of transcription. b. two or more different alternative sigma proteins. c. many different types of promoters. d. glucose.

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Textbook Question

Evaluate these statements about regulation of the lac operon. Select True or False for each statement. T/F The lac operon is transcribed at the highest rate when extracellular glucose and lactose are abundant. T/F The repressor protein is bound to DNA of the operator when lactose is present. T/F A mutation in the operator is likely to prevent transcription of the lac operon under any condition. T/F A mutation that alters the catabolite activator protein is predicted to alter the regulation of many different operons.

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Textbook Question

Predict what would happen to regulation of the lac operon if the lacI gene were moved 50,000 nucleotides upstream of its normal location.

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Textbook Question

IPTG is a molecule with a structure much like lactose. IPTG can be transported into cells by galactoside permease and can bind to the lac repressor protein. However, unlike lactose, IPTG is not broken down by ββ-galactosidase. Predict what would occur to lac operon regulation if IPTG were added to E. coli growth medium containing no glucose or lactose.

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Textbook Question

In a mutant that lacks adenylyl cyclase, the enzyme that synthesizes cAMP, predict which of the following conditions of extracellular lactose and glucose would cause regulation of the lac operon to differ from that of wild-type cells. a. no lactose, no glucose b. no lactose, abundant glucose c. abundant lactose, no glucose d. abundant lactose, abundant glucose

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Textbook Question

X-gal is a colorless, lactose-like molecule that can be split into two fragments by ββ-galactosidase. One of these product molecules creates a blue color. The photograph here shows E. coli colonies growing in a medium that contains X-gal. Find three colonies whose cells have functioning copies of ββ-galactosidase. Find three colonies whose cells might have mutations in the lacZ or the lacY genes. Suppose you analyze the protein-coding sequence of the lacZ and lacY genes of cells from the three mutant colonies and find that these sequences are wild type (normal). What other region of the lac operon might be altered to account for the mutant phenotype of these colonies?

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