1. Imagine a bacterial species in which the methionine (Met)operon is regulated
ID: 5537 • Letter: 1
Question
1. Imagine a bacterial species in which the methionine (Met)operon is regulated only by an attenuator and there is norepressor. In its mode of operation, the methionineattenuator is exactly analogous to the trp attenuator of Ecoli. The relevant portion of the attenuator sequence inthe RNA is5'AAA AUGAUG AUG AUG AUG AUG AUG AUG GACUAA.....3' Attenuator Region 1 Region 2
The translation start site is upstream from this sequence, and theregion shown is in the correct reading frame. What phenotype[Constitutive (expressed all the time),wild type (with attenuation control for Metsynthesis) or Met - (irresponsive to methionineconcentration)] would you expect for each to the types ofmutant RNA below? Explain yourreasoning?
a) 3rd A is deleted
b) 3rd and 4th 'A's are deleted
c) The first three 'A's aredeleted
2. A frameshift mutation occurs near the end of anexon. Does it affect the reading frame of the next exon inthe processed mRNA? Explain youranswer. 1. Imagine a bacterial species in which the methionine (Met)operon is regulated only by an attenuator and there is norepressor. In its mode of operation, the methionineattenuator is exactly analogous to the trp attenuator of Ecoli. The relevant portion of the attenuator sequence inthe RNA is
5'AAA AUGAUG AUG AUG AUG AUG AUG AUG GACUAA.....3' Attenuator Region 1 Region 2
The translation start site is upstream from this sequence, and theregion shown is in the correct reading frame. What phenotype[Constitutive (expressed all the time),wild type (with attenuation control for Metsynthesis) or Met - (irresponsive to methionineconcentration)] would you expect for each to the types ofmutant RNA below? Explain yourreasoning?
a) 3rd A is deleted
b) 3rd and 4th 'A's are deleted
c) The first three 'A's aredeleted
2. A frameshift mutation occurs near the end of anexon. Does it affect the reading frame of the next exon inthe processed mRNA? Explain youranswer.
Explanation / Answer
a. Constitutive : Deletion of A causes a frameshift that switches the reading frame from ATG ATG and so forth to TGA TGA and so forth. TGA is a stop codon,therefore the attenuator will not be translated through and transcription will go unabated.
b. met- Deletion of two A's changes the reading frame from ATG ATG and so forth to GAT GAT and so forth. GAT is an Asp Codon. Therefore translation will proceed through even when the concentration of methionine is very low,and trancription will terminate prematurely.
c. Wildtype: A deletion of all three A's does not change the reading frame.
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