Question

The regulatory proteins are the accessory proteins that interact with RNA polymerase and affect its role in transcription. Which of the following statements is true about regulatory proteins?

• A. They only increase expression.
• B. They only decrease expression.
• C. They interact with RNA polymerase but do not affect the expression.
• D. They can act both as activators and as repressors.

Answer 1

Answer: (D)

The operon is a cistron with gene regulation activity basically observed in the prokaryotes. The operon model of prokaryotic gene regulation was proposed by Jacob and Monod. Operons are groups of genes, coding for related proteins, and are arranged in units. It is the part of the DNA which act as a single regulated unit having one or more structural gene, an operator, a promoter, and a regulator gene.
Operons are mainly of two types, the inducible and repressible that operate in regulating the metabolic pathways. For example, metabolism of lactose, tryptophan, arabinose, etc., when supplied externally in the growth medium.
In the inducible operon, the effector or the inducer molecule binds to the repressor such that it can no more bind to the operator. For example, lac operon.
In the repressible operon, the effector or the co-repressor molecule binds to the repressor such that it can bind to the operator. In this type, the operon gets switched off with the presence of a co-repressor. For example, tryptophan operon.