Identify similarities and differences between an inducible operon and a repressible operon in terms of

the organization of structural genes of the operon.

Key Concepts

Operon Structure

An operon is a cluster of genes under the control of a single promoter, allowing for coordinated expression. In prokaryotes, operons can be classified as inducible or repressible based on their regulatory mechanisms. The structural genes within an operon are transcribed together, producing a single mRNA that encodes multiple proteins, which often function in related pathways.

Inducible Operon

An inducible operon is typically off but can be turned on in response to an inducer molecule. This type of operon, such as the lac operon, allows for the expression of genes involved in metabolizing specific substrates when they are present. The presence of the inducer leads to the inactivation of a repressor protein, enabling transcription of the structural genes.

Repressible Operon

A repressible operon is usually active but can be turned off by a corepressor molecule. This mechanism is exemplified by the trp operon, which regulates the synthesis of tryptophan. When tryptophan levels are high, it binds to the repressor, activating it and inhibiting the transcription of the operon's structural genes, thus preventing unnecessary production.