Lac operon questions for recitation. For the following genotypes indicate whethe
ID: 254385 • Letter: L
Question
Lac operon questions for recitation. For the following genotypes indicate whether beta-galactosidase and permease are produced under the listed environmental conditions. Use the following categories: High: if the normal gene product is produced at a high level Basal: if the normal gene product is produced at a basal level None: if the normal gene product is not produced, or is produced at an extremely low level. Describe HOW the proteins and DNA sequences interact to produce that level(s) of gene products. Model answers for the wildtype genotype have been provided for you in bold. Genotype Beta-galactosidase activi Permease activi lactose present; lactose present; lactose present; lactose present; glucose present glucose absent glucose present glucose absent lac lac lac la Basal High Basal High High levels of both enzymes are produced when lactose is present and glucose is absent because the repressor protein is not bound to the operator, and the CAP-cAMP complex facilitates the binding of RNA polymerase to the promoter. When glucose is present, there is not enough cAMP to facilitate the binding of RNA pol, so protein production is at basal levels. 1 lgcl' lac lac lacZ+ lacy 5lacl lac lacQ lac lac F lgcl lacbt lacQ lacZ lacYExplanation / Answer
Ans.
lacIslacP+lacOclacZ+lacY- /
F' lacI+lacP-lacOclacZ-lacY+
lacI+lacP-lacO+lacZ-lacY- /
F' lacI-lacP+lacO+lacZ-lacY+
explanation -
1- high levels of only beta galactosidase are produced when lactose is present and glucose is absent. wheras normal gene product of the permease gene will not be produced at all as there is a mutation in the permease gene.
2- high levels of both the enzymes will be produced even in the presence of glucose as repressor will not be able to bind to operator site hence RNA polymerase will constitutively transcribe both genes
3- normal gene products for both genes will not be produced as there is a superrepressor mutation in the repressor in which repressor tightly binds to the operator and represses transcription under all conditions.
4- high levels of both the enzymes will be produced even in the presence of glucose as there is a mutation in the operator site due to which repressor will not be able to bind to it and transcription will not be repressed under any condition.
5- normal gene products for both genes will not be produced due to mutation in the promoter site due to which RNA polymerase is not able to bind and initiate transcription.
6- high levels of both the enzymes will be produced even in the presence of glucose as there is a mutation in the operator site due to which repressor will not be able to bind to it and transcription will not be repressed under any condition.
7- normal gene products for beta galactosidase will not be produced as there is mutation in both the genes for beta galactosidase. whereas basal expression of permease in the presence of glucose and high expression in the absence of glucose (and presence of lactose) is due to trans acting repressor.
1 lacI+lacP+lacO+lacZ+lacy- basal high none none 2 lacI-lacP+lacO+lacz+lacY+ high high high high 3 lacIslacP+lacO+lacZ+lacY- none none none none 4 lacIslacP+lacOclacZ+lacY+ high high high high 5 lacI+lacP-lacO+lacZ-lacY+ none none none none 6lacIslacP+lacOclacZ+lacY- /
F' lacI+lacP-lacOclacZ-lacY+
high high high high 7lacI+lacP-lacO+lacZ-lacY- /
F' lacI-lacP+lacO+lacZ-lacY+
none none basal highRelated Questions
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