2. Assume you have identified a new operon in bacteria (which you call the suc operon) that encodes enzymes required for catabolism of the sugar sucrose. The structural genes that are required to breakdown sucrose are transcribed from a promoter (Psuc). One of these enzymes is encoded by the sucS gene. Expression of the operon is controlled by a regulator, called SucR, which binds to an operator (0). Using your knowledge of the lac operon, interpret the results of the following experiments (Table 1) to propose a model describing how the sucrose operon might be regulated. Cell genotype Production of SucS enzyme Without sucrose With sucrose R* O* p* s* R O* p* s* R* O P* s* R O* p* s* / R* Oʻ p* 5 ++ -- -- -- ++ -- R°O* P* S ++ ++ Table 1. Production of SucS enzyme in various strains. “-" in the cell genotype indicates a loss of function mutation, “+" indicates wild type function, two genotypes separated by a / indicate a merodiploid or partial diploid. R° is a mutant version of SucR that always binds to O. Production of SucS enzyme is indicated with “++", and no expression with “–". You may include diagrams in your answer.

2. Assume you have identified a new operon in bacteria (which you call the suc operon) that encodes enzymes required for catabolism of the sugar sucrose. The structural genes that are required to breakdown sucrose are transcribed from a promoter (Psuc). One of these enzymes is encoded by the sucS gene. Expression of the operon is controlled by a regulator, called SucR, which binds to an operator (0). Using your knowledge of the lac operon, interpret the results of the following experiments (Table 1) to propose a model describing how the sucrose operon might be regulated. Cell genotype Production of SucS enzyme Without sucrose With sucrose R* O* p* s* R O* p* s* R* O P* s* R O* p* s* / R* Oʻ p* 5 ++ -- -- -- ++ -- R°O* P* S ++ ++ Table 1. Production of SucS enzyme in various strains. “-" in the cell genotype indicates a loss of function mutation, “+" indicates wild type function, two genotypes separated by a / indicate a merodiploid or partial diploid. R° is a mutant version of SucR that always binds to O. Production of SucS enzyme is indicated with “++", and no expression with “–". You may include diagrams in your answer.

Biology (MindTap Course List)

11th Edition

ISBN:9781337392938

Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg

Publisher:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. Berg

Chapter14: Gene Regulation

Section: Chapter Questions

Problem 13TYU: INTERPRET DATA Develop a simple hypothesis that would explain the behavior of each of the following...

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For the E. coli lac operon, when lactose is present: a. and glucose is absent, cAMP binds and activates catabolicactivator protein (CAP). b. and glucose is absent, the level of cAMP decreases. c. activated CAP binds the repressor protein to remove it from the operator gene. d. the cell prefers lactose over glucose. e. RNA polymerase cannot bind to the promoter.
4) Suppose you have an E. coli in which the gene that codes for the lac repressor protein has been mutated in such a way that the protein produced can bind to both lactose and DNA (at its specific binding site in the lac operon promoter) simultaneously. What effect, if any, would this have on regulation of expression of the lac operon? Briefly (1 sentence) explain why you would predict the effect or lack of effect this mutation would have.
1. What is the default state of the lac operon? a. LacI repressor is sitting on the operator sequence and blocks RNAP from transcribing lacZYA. b. LacI repressor is not in a correct shape to bind to the operator sequence. c. LacI repressor is not produced in the absence of lactose. d. Allolactose is sitting on the operator sequence and blocks RNAP from transcribing lacZYA.
1. A)Explain the mechanism by which the lac operon is sensitive to glucose levels (presence and absence of glucose). B)If glucose levels in the cell are high and lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon?
1. Assuming that the level of glucose is low, a mutation in the repressor associated with the lac operon of E. coli which prevents binding of the repressor to lactose should result in: a. constitutive expression of the lac operon genes b. lack of expression or refuced expression of the lac operon genes under all circumstances c. expression of the genes only when lactose is present d. expression of the genes only when lactose is absent e. lack of expression of the lac operon genes, resulting in an increase in lactose production
1) The logic of the Lac operon was deciphered by using bacterial lac-operon mutants. Crucial to the experiments was creation of partial diploid cells in which operon from a wild-type cell is introduced into the mutant cell [thus there are 2 copies of the operon], and its ability to restore repression is assessed. Three classes of mutants were found that affect expression of the lac operon. Two of these resulted in constitutive expression of the operon, and the other eliminated all expression, even in the presence of lactose. Use the information above to complete the following table indicating with a (Y) yes or (N= No) if enzymatic activity of B-Gal will be detected (protein made and functional). Assume there is no glucose. Remember: Promoter for operon controls ALL genes downstream of it, coding sequence of the genes themselves matter (so if transcription is occurring but structural gene is producing a non-functional protein there will be no activity detected) For the lac operon…
1. a) If glucose is not available and lactose is absent from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)If glucose is not available, but lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)
1. If the above gene is one of the three structural genes of the lac operon that codes for theprotein/ enzyme responsible for breaking lactose into two molecules of simple sugars,a.) what triggers the activation of this gene?b.) what triggers the inactivation of this gene?c.) what substance is attached to the operator region of the operon in the absence ofactivator?d.) what gene is responsible for the synthesis of the substance used to attach in theoperator region in the absence of activator? e.) what substance is attached to the promoter region of the operon in this case?
1) A. What is the difference between a repressible vs, an inducible operon? B. Using diagrams and words, describe how the Lac Operon is regulated by different levels of lactose and glucose. Be sure to show what’s happening at the molecular level, including the roles of lactose, glucose the repressor protein, cAMP and CAP.
1) Assume you have an operon that is repressible. In this case, the rate of synthesis of repressor protein must depend on the level of a) co-repressor b) inducer c) both d) neither
3. How might the regulation of the lac operon change if a point mutation occurred that blocks the ability of the repressor protein (LacI) to bind lactose?
4. What are the effects of the following conditions on Lac operon of bacteria?A)Glucose is absent and lactose is presentB)Glucose is present and lactose is presentC) Glucose is present and lactose is absent