Question

The trp and lac operons are regulated in various ways. How do bacteria regulate transcription of these operons? Sort the statements into the appropriate bins depending on whether or not each operon would be transcribed under the stated conditions. View Available Hint(s)

Answer 1

Hint:lac operon: lactose absent

lac operon: lactose and glucose present

lac operon: lactose present, glucose not

trp operon: tryptophan present

trp operon: tryptophan absent

Answer:

The operon is transcribed when:

Lac operon: lactose present, glucose not

The operon will not be transcribed if

lac operon: lactose absent

trp operon: tryptophan present

Operon is transcribed, but slowed through positive control:

Lac operon: lactose and glucose present

Trp operon: tryptophan absent

Explanation:

The lac operon is controlled by two factors one that acts positively through CAP-cAMP complex and the second that acts negatively through lac repressor that antagonizes binding of RNA polymerase to the promoter.

Negative control:

1.When lactose is absent, the repressor molecule bind the operator site of the lac gene and transcription is turned off.

2. In the presence of lactose, lactose binds to the repressor molecule, the repressor-lactose complex is inactive, the repressor protein does not bind to the operator, and transcription is turned on.

-Positive control:

The lac operon is also regulated by catabolite activator protein (CAP). When glucose is absent, bacteria accumulate cAMP. Bacteria RNA polymerase can only attach to the promoter site when CAP binds cAMP to form CAP-cAMP, hence CAP is a positive regulator.

The trp operon is regulated through negative control mechanism only. When tryptophan is present, the operon genes are not transcribed.