1) The UR operon, which is composed of sequences A, B, C, and D (which may or may not be genes of regulatory sequences), encodes enzymes 1 and 2. Mutations in sequences A, B, C, and D have the following effects listed in the table below. A plus sign (+) indicates that the enzyme is synthesized and a minus sign (−) indicates that the enzyme is not synthesized.| Mutation in sequence | UR present | UR absent ||----------------------|-----------------------------|----------------------------|| | Enzyme 1 | Enzyme 2 | Enzyme 1 | Enzyme 2 || No Mutation | − | − | + | + || A | − | − | − | + || B | + | + | + | + || C | − | − | + | − || D | − | − | − | − |A) Is the UR operon inducible or repressible?B) Indicate which sequence (A, B, C, or D) is part of the following components of the operon: a. Regulator gene ________________ b. Promoter ________________ c. Structural gene for Enzyme 1 ________________ d. Structural gene for Enzyme 2 ________________

Name: 1) The UR operon, which is composed of sequences A, B, C, and D (whic
Uploaded: 2024-03-20T06:42:41.000Z
Channel: Bartleby
Description: 1) The UR operon, which is composed of sequences A, B, C, and D (which may or may not be genes of regulatory sequences), encodes enzymes 1 and 2. Mutations in sequences A, B, C, and D have the following effects listed in the table below. A plus sign

An operon may be considered as a group of certain genes which function together so as to regulate the transcription of several structural genes (in prokaryotes the transcription unit is polycistronic, multiple polypeptide chain coding sequences within a single transcription unit). An operon will consist of the structural genes (polycistronic, here one polypeptide code for enzyme 1 and the second polypeptide code for enzyme 2), an operator sequence, a promoter and a regulator gene. The regulator gene of the operon will produce a protein which is exclusively meant for regulating the transcription of structural gene. This regulator protein specifically bind the operator. If this binding prevent transcription, it is called negative regulation and such a regulator protein is called Repressor protein. On the other hand if the regulator protein binding to the operator helps RNA polymerase to gain access to the promoter and thereby undertake transcription , it is called positive regulation and the regulator protein is called an Activator protein. If an operon with intrinsic negative regulation (i.e. regulator gene is a repressor) can be altered to transcribe the mRNA (i.e. coded by the structural gene), then such an operon is called inducible. If an operon with intrinsic positive regulation (i.e. regulator gene is an activator) can be altered to prevent the transcription of the mRNA and hence no protein (enzymes in this case), then such an operon is called repressible.A) When there was no mutation and the operon was present, neither of the enzymes were produced whereas both enzymes were produced when the operon was absent. So the operon has intrinsic Negative regulation (i.e. the regulatory protein is a repressor). Then when we mutated Gene B , both the enzymes were produced in the presence of the operon. This indicate that Gene B is a regulator gene with negative regulation (i.e. a repressor gene) and the operon was induced to produce the enzymes when the repressor gene got silenced via mutation. So UR operon is 'inducible'. B) a) We have already figured out that Gene B is a regulator gene. b) If the promoter sequence undergoes a unfavorable mutation, then the RNA polymerase wont be able to bind to it and the transcription wont take place and no enzyme will be produced, with or without operon. A mutation to Gene D resulted in the production of neither enzymes in the presence and absence of the operon. So Gene D is the promoter. c) A mutation to Gene A meant no enzyme 1 got produced even in the absence of the operon. So Gene A is the structural gene for Enzyme 1. Note: Enzyme 1 and 2 wont be produced when the repressor gene B is active in the presence of operon even if the Structural genes for enzymes 1 and 2 are functional (not mutated). d) A mutation to Gene C meant no enzyme 2 got produced even in the absence of the operon. So Gene C is the structural gene for Enzyme 2.