12th Class Biology Molecular basis of inheritance

  • question_answer 42)   In E. coli, the lac operon gets switched on when      (a) lactose is present and it binds to there pressor (b) repressor binds to operator (c) RNA polymerase binds to the operator (d) lactose is present and it binds to RNA polymerase


       (a)   In case of lactose presence (i) Lactose acts as an inducer which binds to the repressor and forms an inactive repressor. (ii) The repressor fails to bind to the operator region. (iii) The RNA polymerase binds to the operator and transcript lac mRNA. (iv) lac mRNA is polycistronic, i.e., produces all three enzymes, -galactosidase, permeaseand transacetylase. (v) The lac operon is switched on. In case of lactose absence (i) When lactose is absent, i gene regulates and produces repressor mRNA which translate repression. (ii) The repressor protein binds to the operator region of the operon and as a resultprevents RNA polymerase to bind to the operon. (iii) The operon is switched off.  

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