If a particular operon encodes enzymes for making an essential amino acid and is regulated like the trp operon, then
a. The amino acid inactivates the repressor.
b. The repressor is active in the absence of the amino acid.
c. The amino acid acts as a corepressor.
d. The amino acid turns on transcription of the operon.

Verified step by step guidance

1. Understand the function of the trp operon: It is a repressible operon that is typically active but can be turned off when the amino acid tryptophan is present.
2. Identify the role of tryptophan in the trp operon: Tryptophan acts as a corepressor, which means it binds to the repressor protein, activating it.
3. Recognize the state of the repressor: In the absence of tryptophan, the repressor is inactive, allowing transcription to occur.
4. Determine the effect of the amino acid on the operon: When the amino acid is present, it binds to the repressor, activating it and stopping transcription.
5. Apply this understanding to the problem: If the operon in question is regulated like the trp operon, the amino acid would act as a corepressor, similar to tryptophan in the trp operon.

Key Concepts

Operon Structure

An operon is a cluster of genes under the control of a single promoter, allowing for coordinated regulation of gene expression. In prokaryotes, operons enable the efficient use of resources by regulating the transcription of multiple genes that encode proteins with related functions, such as enzymes involved in a metabolic pathway.

Repressor Proteins

Repressor proteins are regulatory proteins that bind to specific DNA sequences, inhibiting the transcription of target genes. In the context of operons, the presence or absence of certain metabolites, like amino acids, can influence the activity of these repressors, determining whether the operon is active or inactive.

Corepressor Function

A corepressor is a small molecule that binds to a repressor protein, enhancing its ability to bind to the operator region of an operon. In the case of the trp operon, the presence of tryptophan acts as a corepressor, allowing the repressor to effectively block transcription when the amino acid is abundant, thus regulating the synthesis of enzymes needed for its production.