Multiple choice

In the function of the lac operon in E. coli, the lac genes are transcribed in the presence of lactose because

  1. RNA polymerase binds to the operator

  2. the repressor binds to the promoter

  3. an isomer of lactose binds to the repressor

  4. CAP does not bind to the operator

  5. of the absence of cAMP
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When lactose is present, some of it is converted to allolactose, which binds to the lac repressor protein. This binding causes the repressor to change shape and release from the operator site, allowing RNA polymerase to transcribe the lac genes. CAP (catabolite activator protein) actually binds to the promoter, not the operator.

Keep practicing — related questions