The lac operonलैक ओपेरॉन

NCERT Fig 5.14 · Class 12 Biology · Chapter 5 · interactive diagram

Parts and their functions

• i gene (regulatory) (i जीन (नियामक)) — Codes for the repressor; i = inhibitor (not inducer). Expressed constitutively.
• Promoter (p) (उन्नायक (p)) — Where RNA polymerase binds.
• Operator (o) (प्रचालक (o)) — Next to the promoter; the lac repressor binds here specifically.
• z gene (z जीन) — β-galactosidase: hydrolyses lactose into galactose and glucose.
• y gene (y जीन) — Permease: increases permeability of the cell to β-galactosides.
• a gene (a जीन) — Transacetylase.
• Repressor (दमनकर) — Binds the operator when there is no lactose; the inducer inactivates it.
• Inducer (lactose / allolactose) (प्रेरक (लैक्टोज़ / ऐलोलैक्टोज़)) — Binds and inactivates the repressor, switching the operon on.
• RNA polymerase (आरएनए पॉलीमरेज़) — Transcribes z, y, a once the operator is free.
• Polycistronic lac mRNA (बहुसमपारी लैक mRNA) — One mRNA for z, y and a.

Steps

1. No lactose: repressor binds the operator — operon OFF (negative regulation).
2. Lactose present: inducer inactivates the repressor — z, y, a transcribed.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 5.14. Report a mistake