Question

According to the operon concept, the regulator gene regulates chemical reactions in the cell by

• A. Inactivating enzyme in the reaction
• B. Inhibiting the substrate in the reaction
• C. Inhibiting transcription of mRNA
• D. Inhibiting the migration of mRNA into the cytoplasm

Answer 1

Answer: (C)

Inhibiting transcription of mRNA

According to lac operon concept, regulator gene regulates the expression of structural genes by its protein product that are mostly transcription factors. These transcription factors, the regulatory protein, bind to the operator region which is located just upstream the binding site of the RNA polymerase and hence, prevent the binding and transcription. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site. Hence, regulator gene regulates the expression of structural genes by pre-transcriptionally, not post-transcriptionally by inactivating enzyme/substrate in the reaction or by inhibiting the migration of mRNA into the cytoplasm. Option C is correct answer.