Answer: The repressor protein binds the operator and blocks transcription.
- A RNA polymerase is degraded before it can bind the promoter region
- B The repressor protein binds the operator and blocks transcription
- C The promoter sequence has been permanently deleted from the operon
- D The structural genes z, y, and a are entirely absent from the operon
Correct answer: B. The repressor protein binds the operator and blocks transcription
Explanation: Without an inducer, the active repressor protein binds to the operator region, physically blocking RNA polymerase from transcribing the z, y, and a genes.
Helicase unwinds the double helix at the replication fork; one new strand (leading) is synthesised continuously toward the fork, while the other (lagging) must be made in short, separate Okazaki fragments because DNA polymerase only adds nucleotides 5'→3'.
Concept context
DNA structure, replication, transcription, translation, the genetic code, and gene regulation (lac operon). The single most important chapter for NEET molecular biology.