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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance5 Marks
Question
Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow.
  1. Identify and name the regulatory gene in this operon. Explain its role in 'switching off the operon.
  2. Why is lac operon's regulation referred to as negative regulation?
  3. Name the inducer molecule and the products of the genes 'z' and 'y of the operon. Write the function of these gene products.
✓

Answer

  1. Regulatory gene in this operon is i gene. Role of regulatory gene in switching off operon is as follows:
  1. It codes for the repressor protein of the operon, which is synthesised constitutively.
  2. The repressor has affinity for the operator gene. It binds to operator and prevents the RNA polymerase from transcribing the structural genes.
  1. When repressor binds to the operator, the operon is switched off and transcription is stopped. So, it is called a negative regulation.
  2. Lactose is an inducer molecule.
  1. Z gene codes for B-galactosidase (b-gal), that helps in the hydrolysis of disacchoride into its monomeric units, i.e. lactose into galactose and glucose.
  2. Y gene codes for pwemease, that increases the permeability of the cell to B-galactosides.
  3. a gene codes for a transacetylase.

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