question_answer

In the operon system, the represser protein can bind only with the:

A)  structural genes

B)  regulator gene

C)  operator gene  

D)  promoter gene

Correct Answer: C

Solution :

Jacob and Monod (1961) on the basis of their study on the indusible system for the synthesis of \[\text{ }\!\!\beta\!\!\text{ -}\]glactosidase enzyme in E-coli. proposed a model in order to explain the induction or repression of enzyme synthesis. This model is popularly known as operon model. Three enzymes are required for lactose utilization in E. coli. The three genes (called structural genes or cistrons) coding for these enzymes. In lac operon the regulator site regularly transcribes for synthesis of a lac represser protein of 36 amino acid residue. In absecne of lactose this protein binds to the operator site which in fact includes a part of the promoter site also.