Principles of Biology
2nd Edition
ISBN: 9781259875120
Author: Robert Brooker, Eric P. Widmaier Dr., Linda Graham Dr. Ph.D., Peter Stiling Dr. Ph.D.
Publisher: McGraw-Hill Education
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Chapter 12.2, Problem 1TYK
Summary Introduction
Introduction:
In the presence of lactose in the environment, bacteria tend to produce lactose-using enzymes at a higher rate. However, in the absence of lactose also bacteria tend to form these enzymes, but in very small amounts. If the lac repressor is absent, there would be no control of producing the lactose-using enzymes. Therefore, either in the presence or absence of lactose in the environment, if there is no lac repressor the lactose-using enzymes will be produced continuously. This means, the lac operon is going to be expressed in any case.
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Let’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation may block the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operon in a way that prevents the repressor protein from binding to the operator. How would you distinguish between these two possibilities?
Let’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation mayblock the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operator in a way that prevents lac repressor from binding to the operator. How would you distinguish between these two possibilities?
What would happen if the operator sequence of the lac operon contained a mutation that prevented the repressor protein from binding the operator? (Explain what would happen both in the presence and absence of lactose)
Chapter 12 Solutions
Principles of Biology
Ch. 12.1 - How does gene regulation underlie the different...Ch. 12.1 - Prob. 1TYKCh. 12.1 - The most common point of gene regulation in...Ch. 12.2 - Which genes are under the control of the lac...Ch. 12.2 - Prob. 2CCCh. 12.2 - Prob. 1BCCh. 12.2 - Prob. 1TYKCh. 12.3 - Prob. 1CCCh. 12.3 - Prob. 1TYKCh. 12.3 - Prob. 2TYK
Ch. 12.4 - Prob. 1CCCh. 12.4 - Prob. 1BCCh. 12.4 - A chromatin-remodeling complex may change the...Ch. 12.4 - Prob. 2TYKCh. 12.5 - What is the biological advantage of alternative...Ch. 12.5 - Prob. 2CCCh. 12.5 - Prob. 1TYKCh. 12.5 - Prob. 2TYKCh. 12 - Genes that are expressed at all times at...Ch. 12 - Prob. 2TYCh. 12 - Transcription factors that bind to DNA and...Ch. 12 - Prob. 4TYCh. 12 - Prob. 5TYCh. 12 - Prob. 6TYCh. 12 - Prob. 7TYCh. 12 - Prob. 8TYCh. 12 - Prob. 9TYCh. 12 - Prob. 10TYCh. 12 - What is the difference between inducible and...Ch. 12 - Transcriptional regulation often involves a...Ch. 12 - PRINCIPLES A principle of biology is that the...Ch. 12 - Discuss the advantages and disadvantages of...Ch. 12 - Prob. 2CBQ
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- A mutation that inactivates the repressor gene of the lac operon results in (a) the continuous transcription of the structural genes (b) no transcription of the structural genes (c) the binding of the repressor to the operator (d) no production of RNA polymerase (e) no difference in the rate of transcriptionarrow_forwardMutations may have an effect on the expression of the lac operon and the trp operon. Would the following mutations have a cis- or transeffect on the expression of the protein-encoding genes in the operon? A. A mutation in the operator site that prevents lac repressor from binding to it B. A mutation in the lacI gene that prevents lac repressor from binding to DNA C. A mutation in the trpL gene that prevents attenuationarrow_forwardIf 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?arrow_forward
- If an abnormal repressor protein could still bind allolactose but the binding of allolactose did not alter the conformation of the repressor protein, how would the expression of the lac operon be affected?arrow_forwardA mutation in the repressor LacI causes it to lose the ability to bind its effector, allolactose. What will be the effect of this mutation in the presence of allolactose (assume glucose is absent)? a) LacI cannot bind to the lac operator (lacO) and transcription of the lac operon is blockedb) LacI is permanently bound to the lac operator (lacO) and transcription of the lac operon is blocked c) LacI cannot bind to the lac operator (lacO) and transcription of the lac operon increasesd) LacI is permanently bound to the lac operator (lacO) and transcription of the lac operon increasesarrow_forwardHow does the repressor protein contribute to selective expression of the structural genes Z, Y, and A in the lac operon? The repressor protein is only expressed when lactose is present. The repressor is always expressed. It blocks transcription when lactose is present. The repressor is always expressed. It allows transcription when lactose is absent. The repressor is always expressed. It blocks transcription when lactose is absent. The repressor protein is only expressed when lactose is absent.arrow_forward
- Under what conditions would you expect to see high levels of expression of the structural genes in the lac operon? Group of answer choices Lactose is absent and glucose is absent Lactose is absent and glucose is present Lactose is present and glucose is present None of these Lactose is present and glucose is absentarrow_forwardIn the lac operon, the lacZ gene codes for an enzyme called ____________, which catalyze the breakdown of the sugar __________ into monosaccharides. This enzyme can also hydrolyze the sugar analog ____________, which produces blue pigments following its breakdown. Since the lac operon is not always on the bacterial cells, we add the chemical ________ which prevents the lac depressor from binding to the operators, leading to constitutive expression of the operon.arrow_forwardIf 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?arrow_forward
- In the lac operon (below), how will expression of the genes lacZ and lacy be effect by a mutation in the repressor protein (encoded by lach) that prevents it from binding the operator sequence (lacO) in the absence of lactose? Explain the answerarrow_forwardIf the above gene is one of the three structural genes of the lac operon that codes for the protein/ enzyme responsible for breaking lactose into two molecules of simple sugars, what triggers the activation of this gene? a. Absence of Inhibitory protein b. Presence of lactose c. Absence of lactose d. Presence of Inhibitory protein e. Absence of Regulatory proteinarrow_forwardWhen lactose is first introduced into the medium, the lac operon is not induced and thus permease isn't induced. How is it possible for lactose to enter the cell before the lac operon is induced? While the lac operon is not induced yet, lactose has many different ways to get into the cells without the need of permease. While the lac operon is not induced yet, lactose breaks down outside the cell into smaller components in order to get into the cell and then the components reassemble into lactose again inside the cell so that the induction can occur. While the lac operon is not induced yet, there is always a very high level of permease and beta galactosidase in the cell. While the lac operon is not induced yet, there is full level expression most of the time which allows a sufficient amount of permease to be expressed. This allows lactose to enter the cell. While the lac operon is not induced yet, there is low level expression most of the time which…arrow_forward
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