Question

The trp operon in E.coli regulates genes that code for enzymes required for synthesis of the amino acid tryptophan. The trp operon is a repressible operon. When tryptophan is not available in the environment, the trp repressor protein is _________. Therefore, RNA polymerase can bind to the __________ to begin transcription.

A) inactive, promoter
B) active, promoter
C) inactive, operator
D) active, operator

Answer 1

When tryptophan is not available, the trp repressor protein is inactive, allowing RNA polymerase to bind to the promoter and initiate transcription. Option A is the answer.

Step-by-step explanation:

The trp operon in E. coli is a regulatory system that controls the expression of genes involved in tryptophan synthesis. It operates as a repressible operon, meaning that it is usually on but can be turned off. When tryptophan is scarce, the trp repressor protein is inactive. In this state, it cannot bind to the operator region of the operon.

With the trp repressor inactive, RNA polymerase can freely bind to the promoter region, initiating transcription of the genes responsible for tryptophan synthesis. This mechanism ensures that the synthesis of tryptophan occurs only when the amino acid is needed and is not already present in sufficient quantities.

Option A is the answer.