AP Biology : Transcription
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Example Question #31 : Transcription
The lac operon contains the lac repressor, which binds to the operator to inhibit transcription. What type of operon is this, and how can transcription of the genes proceed?
Repressible; a repressor binding to the repressor will allow transcription
Repressible; a repressor binding to the repressor will allow transcription
Inducible; an inducer binding to the repressor will allow transcription
Inducible; an inducer binding to the operator will allow transcription
Inducible; an inducer binding to the repressor will allow transcription
The lac operon is inducible, meaning that it is normally turned off or not transcribing genes (due to the repressor binding to the operator region). However, transcription can proceed if an inducer molecule (in the case of the lac operon this will be allolactose) binds to the repressor, preventing the repressor from binding to the operator region and thus allow RNA polymerase to transcribe the genes.
Example Question #32 : Transcription
The trp operon is normally active or turned “on.” However, when tryptophan is present, it binds to a repressor molecule, activating it, and causing inhibition of transcription of the genes. What type of molecule is tryptophan, and what type of operon is the trp operon?
inducer; inducible
corepressor; repressible
corepressor; inducible
repressor; repressible
corepressor; repressible
The trp operon is normally on, meaning that the genes are normally being transcribed by RNA polymerase. Thus, this is a repressible operon. The operon can be turned off or repressed if another molecule (called a corepressor) binds to a repressor and causes the repressor to bind to the operator region (in the case of the trp operon this molecule is tryptophan; it binds to a repressor causing the repressor to bind to the operator region and prevents RNA polymerase from transcribing the genes).
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