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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance5 Marks
Question
Describe Lac ‘Operon’.
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Answer


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Lac operon consists of the following components:
(1) Regulator gene:

  • Regulator gene precedes the promoter gene.
  • It may not be present immediately adjacent to operator gene.
  • Regulator gene codes for a repressor protein which binds with operator gene and represses (stops) its action.

(2) Promoter gene:

  • It precedes the operator gene.
  • It is present adjacent to operator gene.
  • RNA Polymerase enzyme binds at promoter site.
  • Promoter gene base sequence determines which strand of DNA acts a template.

(3) Operator gene:

  • It precedes the structural genes.
  • When operator gene is turned on by an inducer, the structural genes get transcribed to form m-RNA.

(4) Structural gene:

  • There are 3 structural genes in the sequence lac-Z, lac-Y and lac-A.
  • Enzymes produced are β-galactosidase, β-galactoside permease and transacetylase respectively.
    Inducer Allolactose acts as an inducer. It inactivates the repressor by binding with it.

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