LABORATORY REVIEW
MOLECULAR BIOLOGY
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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glucose sensor
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start acting as repressor when glucose is present
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block transcription of operon in certain condition
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bind to isomer of allalactose
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Detailed explanation-1: -The lac repressor acts as a lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lac repressor senses lactose indirectly, through its isomer allolactose. Catabolite activator protein (CAP) acts as a glucose sensor.
Detailed explanation-2: -The protein that inhibits transcription of the lac operon is a tetramer with four identical subunits called lac repressor. The lac repressor is encoded by the lacI gene, located upstream of the lac operon and has its own promoter.
Detailed explanation-3: -lac Repressor blocks transcribing RNA polymerase and terminates transcription.
Detailed explanation-4: -The lac operon is repressed by LacI, encoded by lacI. The lacI gene is upstream of lacZYA and faces in the opposite direction. The repressor, LacI, binds to the operator sequence upstream of lacZYA and prevents transcription of those genes unless the inducer molecule is present.
Detailed explanation-5: -In the absence of lactose, the lac repressor, lacI, halts production of the enzymes encoded by the lac operon. The lac repressor is always expressed, unless a co-inducer binds to it. In other words, it is transcribed only in the presence of small co-inducer molecules.