Question

Name the repressor of the lac operon.

Hint:

The lacI gene codes for the repressor protein, which regulates the lac operon in response to the presence or absence of lactose.

Answer 1

Step 1: Understanding the lac operon.
The lac operon is a set of genes involved in the metabolism of lactose in bacteria. In the absence of lactose, the lac operon is repressed by a protein called the lac repressor, which is encoded by the lacI gene. The lac repressor binds to the operator region of the lac operon, preventing transcription of the downstream genes. When lactose is present, it binds to the repressor and inactivates it, allowing transcription to proceed.
Step 2: Conclusion.
Therefore, the repressor of the lac operon is the protein encoded by the lacI gene.

Answer 2

Step 1: The lac operon is a group of genes bacteria use to digest lactose.

Step 2: When there's no lactose around, a protein blocks these genes from being switched on.

Step 3: This blocking protein is called the lac repressor, made from the lacI gene.

Step 4: When lactose appears, it binds to the repressor and switches it off, letting the genes turn on.

Answer 3

Working backward from induction.
When lactose is added to the medium, transcription of the lac operon switches on because lactose (via allolactose) binds to and inactivates a protein that was sitting on the operator, blocking RNA polymerase. That protein, which must be removed before the operon can be transcribed, is the lac repressor encoded by the lacI gene, confirming it is the operon's repressor.