AP Biology : Understand regulation of transcription

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #22 : Transcription

Which of the following binds to the repressor of an operon to prevent the repressor from binding to the operator region?

Possible Answers:

unrepressor

inducer

activator

corepressor

Correct answer:

inducer

Explanation:

A repressor is a molecule that binds to the operator region of a gene and prevents RNA polymerase from transcribing the genes. An inducer can bind to a repressor, preventing the repressor from binding to the operator region, and thus allowing RNA polymerase to transcribe the genes.

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?

Possible Answers:

Inducible; an inducer binding to the repressor will allow transcription

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 operator will allow transcription

Correct answer:

Inducible; an inducer binding to the repressor will allow transcription

Explanation:

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 #181 : Dna, Rna, And Proteins

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?

Possible Answers:

corepressor; inducible

inducer; inducible

repressor; repressible

corepressor; repressible

Correct answer:

corepressor; repressible

Explanation:

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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