Molecular Basis of Inheritance

Gene expression and regulation - lac operon

  1. Genes are of 2 types basically – (I) Constitutive / housekeeping [which are in constart expression] ; (ii) non constitutive / smart / luxury genes [They remain silent , whenever needed it gets expressed]
  2. Smart genes are of 2 types – (i) Inducible(lac operon) (ii) repressible (Trp operon)
  3. Segment of genetic material that act as regulating unit of a gene is called operon.
  4. Lac operon is present in all bacterial cells for the purpose of utilisation of lactose.
  5. Three structural genes located in bacteria are lacZ, lacY, lac A out of which lacz expresses an enzyme β-gal actosidase which converts lactose into glucose and galactose-lacy produces permease and lacA produces transacetylase
  6. When lactose is absent in the medium, the repressor produced in lac operon binds with operator. So RNA polymerase can’t move over the structural genes and hence all the 3 genes are not expressed.
  7. When lactose is present in the medium, lactose molecule binds with repressor and it fails to bind to operator and hence promoter region is bound with RNA polymerase and it freely moves within the 3 genes and gets expressed
  8. Lactose induces the operon to turn On the cycle and hence the operon is called inducible operon (catabolic pathway)
  9. Regulation of gene expression in eukaryotes is proposed by Britten and Davidson as gene battery model.

Watch this video for the topic from 0:50 to 45:00

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