lac operon expression question! Is (super-repressor): act \"in trans\", because
ID: 301155 • Letter: L
Question
lac operon expression question!
Is (super-repressor): act "in trans", because it's a diffusible protein and could affect either strand.
Oc (constitutive operator): act "in cis" to cause constitutive.
Please explain about the expression of Beta-galactosidase (Lac Z) and Permease (LacY) in different situations, and the third one, you should explain both the presence and absence of lactose while glucose is absent. Please fully explain the reason why do you think like that (Step by step).
Thanks in advance!!!!!
Explanation / Answer
Note: 1.) The mutations that act 'in trans' are generally protein mutations and form diffusible products.
2.) The mutations that act 'in Cis' are generally mutations in RNA or DNA sequences.
3.) In Is mutation, the super repressor protein prevent the transcription by always binding to the operator sequence. In Oc mutation, the operator sequence is mutated and hence repressor can not bind to the operator which keeps the gene always ON, transcription never stops.
Answer A: IsP+O+Z+Y+/I+P+OCZ+Y- this genotype represent a merodepliod stage.
No transcription will occur in Chromosome 1 due to super repressor. Hence, beta-galactosidase (Lac Z) and permease (Lac Y) will not be expressed from first chromosome. However, Is mutation is dominant over the wild type I+ and can diffuse to repress other chromosome. But, since second choromosome has constitutive phenotype (mutation in DNA sequence), super repressor/repressor can not bind to it. Beta-galactosidase (Lac Z) will be expressed by the second chromosome and due to absence of permease gene (Lac Y), no permease will be expressed.
Overall, only Beta-galactosidase will be expressed in presence of lactose.
Answer B: I+P+O+Z-Y+/I+P-OcZ+Y- represent a merodeploid stage.
Chromosome 1 will express permease (Lac Y) and no Beta-galactosidase (Lac Z) as lac Z is absent. Chromosome 2 has no promoter and since operator acts 'in Cis', and only affect genes that are linked to the promoter, therefore, No transcription will occur. Both Beta-galactosidase and permase are not expressed.
Over all, only permease (Lac Y) is expressed in presence of lactose.
Answer C: I+P+O+Z-Y+/IsP-OcZ+Y- represent a merodeploid stage.
In presence of lactose, Chromosome 1 will undergo transcription and express permease (Lac Y) but not Beta-galactosidase (LacZ) as the lac Z gene is absent. Chromosome 2 is a bust as it does not have a functional promoter and operator acts 'in Cis', hence there will not be any transcription even when lactose is present in the medium. No enzymes are expressed. Overall, only permease is expressed (by Chromosome 1).
In absence of lactose, no transcription of genes will occur in Chromosome 1 as repressor will bind to the operator and in absence of inducer i.e., lactose, repressor can not be kicked off to start the transcription. Chromosome 2 is non-function due to absence of promotor, hence no transcription will take place. Both Beta-galactosidase (Lac Z) and (Lac Y) will NOT be expressed.
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