Which of the following statements concerning the regulatory genes (R), associated with the lac operon are incorrect? I. m RNA is transcribed from the R gene whether lactose is present or not. II. m RNA is transcribed from the R gene only when the lactose is present. III. m RNA is transcribed from the R gene only when the lactose is not present. IV. Lactose inhibits the translation of R gene m RNA.

Question

Which of the following statements concerning the regulatory genes (R), associated with the lac operon are incorrect? I. m RNA is transcribed from the R gene whether lactose is present or not. II. m RNA is transcribed from the R gene only when the lactose is present. III. m RNA is transcribed from the R gene only when the lactose is not present. IV. Lactose inhibits the translation of R gene m RNA. (A) I and II (B) II and III (C) III and IV (D) II, III and IV

Tardigrade Admin · Accepted Answer

Statement II, III and IV are incorrect and only statement I is correct.
This can be explained as in lac operon model, regulatory gene is continuously working, whether lactose (inducer) is present or not. It transcribes

m RN A

which codes for repressor.
When this repressor binds with lactose (inducers) it inhibits translation of operator gene (not R gene).
Thus, lactose presence affects operator gene not

R

gene.