The resulting phenotype when each mutant is transformed using a plasmid that carries the wild-type TrpR (tryptophan R) gene or the wild-type operator region. Introduction: Wild type trp gene refers to the original trp gene which means the gene without any mutation. The mutant gene is manipulated in a way that its functioning becomes altered. Trp repressor binds to the operator gene and terminates the translation in the presence of high levels of tryptophan. In the case of low levels of tryptophan, synthesis of mRNA (messenger ribonucleic acid) occurs.

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Chapter 10, Problem 2TQ

Summary Introduction

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The resulting phenotype when each mutant is transformed using a plasmid that carries the wild-type TrpR (tryptophan R) gene or the wild-type operator region.

Introduction:

Wild type trp gene refers to the original trp gene which means the gene without any mutation. The mutant gene is manipulated in a way that its functioning becomes altered. Trp repressor binds to the operator gene and terminates the translation in the presence of high levels of tryptophan. In the case of low levels of tryptophan, synthesis of mRNA (messenger ribonucleic acid) occurs.

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Which of the following describes the lac operon in E. coli when lactose and glucose is present in the culture medium? Select one: a. CAP inactive and RNA polymerase does not completely bind to the promoter of the lac operon and transcription of lactose-metabolizing enzymes decreases. b. CAP is active and RNA polymerase binds completely to the promoter of the lac operon and transcription of lactose-metabolizing enzymes decreases. c. Catabolite activator protein (CAP) inactive and RNA polymerase does not completely bind to the promoter of the lac operon and transcription of lactose-metabolizing enzymes increases. d. CAP is active and RNA polymerase binds completely to the promoter of the lac operon and transcription of lactose-metabolizing enzymes increases.

The map of the lac operon is shown below. Consider the following examples that include both haploids and partial diploids and explain in each scenario whether the repressor can bind and regulate expression and whether or not the lac operon is expressed. For partial diploids the plasmid is indicated by the F’. I+ O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ / F’ I+ O+ Z+ Y+ I- O+ Z+ Y+ I+ Oc Z+ Y+

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?