Lac Operon Repression & Gene Regulation — NEET Biology
✅ Asked in NEET 2023The component that binds to the operator region of an operon and prevents RNA polymerase from transcribing the operon is: (NEET 2023)
The component that binds to the operator region of an operon and prevents RNA polymerase from transcribing the operon is: (NEET 2023)
In an E. coli strain, i gene gets mutated and its product cannot bind the inducer molecule. If lactose is provided, what will be the outcome? (NEET 2022)
Answer & NCERT explanation
Correct answer: C — Repressor protein
The repressor protein binds to the operator region and prevents RNA polymerase from transcribing the operon according to NCERT. In lac operon, when lactose is absent, the repressor protein binds tightly to the operator sequence, physically blocking RNA polymerase access to structural genes. Promoter is where RNA polymerase binds, inducer removes repressor, and regulator protein is a general term.
Read more NCERT concept on the PYQ
The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds. Essentially, regulation of lac operon can also be visualised as regulation of enzyme synthesis by its substrate.
The core concept NTA tests is how the repressor protein blocks transcription by binding to the operator region, and how an inducer (lactose/allolactose) inactivates the repressor to allow transcription. Students commonly mistake the mechanism—they think the inducer directly activates transcription instead of understanding it inactivates the repressor. The key trap is confusing negative regulation (repressor blocking) with positive regulation (activator promoting). Remember: In the lac operon, the inducer removes the 'brake' (repressor) rather than pressing the 'accelerator'—this is why it's called negative inducible regulation. This appears repeatedly in NEET because understanding operon regulation is fundamental to molecular biology.
What does NCERT say about repressor operon synthesised all-the-time?
Has this concept appeared in NEET?
Which chapter is this from?
Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.