A theoretical operon (amo) in E. coil contains several structural genes encoding
ID: 89714 • Letter: A
Question
A theoretical operon (amo) in E. coil contains several structural genes encoding enzymes involved in the biosynthesis of a particular amino acid. Unlike the lac operon, in which the repressor gene is separate from the operon itself, for the amo operon, the repressor gene is found within the operon itself. When the end product amino acid is present, it binds to the repressor, and this complex binds to the operator, repressing the operon. In the absence of the amino acid, the repressor fails to bind to the operator, and transcription proceeds. Characterize this operon, comparing it to the regulation of the lac and trp operons. Be sure to discuss how regulation is affected by having the repressor gene as part of the operon. Then, consider the following mutations: a) Mutation in the operator region; b) Mutation in the promoter region; c) Mutation in the repressor gene. In each case, state whether the operon will be transcribed or not, and describe how the mutation affects the regulation of the operon. Compare each response to the equivalent situation in the lac and trp operons.Explanation / Answer
amo operon has 3 genes basically: C,A and B with inter geneic space between all three genes. This space is occupied by promoter operator and terminator/ repressor. The regulation of protein synthesis acts in a cycle where the availability of end product stops transcription by binding to the repressor.
In lac operon, there is no transcription in absence of lactose as the repressor binds to the operator region from outside, and RNA polymerase cannot do transcription . In presence of lactose, Allolactose induces transcription by binding to repressor so that the repressor can no longer bind to operator.
When the repressor is present outside the operon it provides better functioning and better regulation of all the genes in the operon. Any mutation if occurs inside the operon, can adversely affect the functioning of whole cycle in amo operon.
Mutation in operator gene will adversely affect the binding of repressor to operator. Binding will be unsuccessful and improper and may prove insufficient in stopping transcription.
Mutation in promoter gene will adversely affect binding of RNA polymerase to promoter. It can halt the transcription as the mutant promoter cannot initiate the transcription.
Mutation in repressor gene again will cause improper binding to operator hence may lead to either uncontrolled transcription or no transcription at all.
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