1. If the lac I protein is bound to DNA, a. RNA polymerase binds the promoter an
ID: 166142 • Letter: 1
Question
1. If the lac I protein is bound to DNA,
a. RNA polymerase binds the promoter and the lac operon is transcribed
b. RNA polymerase cannot bind the promoter and the lac operon is not transcribed
c. the lac operon is transcribed whether or not RNA polymerase binds the promoter
d. the lac I protein must also be bound to lactose
2. If the lac I gene is mutated so it cannot encode a functional protein,
a. lac Z and lac Y would never be expressed
b. lac Z and lac Y would always be expressed
c. lac Z and lac Y would be induced by lactose
d. lac Z and lac Y would be repressed by lactose
Explanation / Answer
1. B. RNA polymerase do not bind to the promoter and lac operon is not transcribed.
( lacI protein is a repressor protein that binds with DNA promoter region and does not allow RNA polymerase to bind with promoter to transcribe the genes)
2. B. Lac Y and Z would always be expressed.
If LacI gene is mutated than repressor protein will not be formed. In absence of repressor protein RNA polymerase will be able to bind with promoter region and will keep transcribing the genes. Presence or absence of lactose will have no control over switching on and off of the genes.
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