Identify similarities and differences between an inducible operon and a repressible operon in terms of
The organization of structural genes of the operon.

Verified step by step guidance

1. Understand the concept of an operon: An operon is a cluster of genes under the control of a single promoter and regulatory elements. It is a key feature of prokaryotic gene regulation.
2. Define an inducible operon: An inducible operon is typically off by default and requires the presence of an inducer molecule to activate transcription. A classic example is the lac operon in *E. coli*.
3. Define a repressible operon: A repressible operon is typically on by default and can be turned off when a specific molecule (corepressor) binds to the repressor protein. A classic example is the trp operon in *E. coli*.
4. Compare the organization of structural genes: Both inducible and repressible operons have structural genes organized in a contiguous sequence, which are transcribed together as a single mRNA (polycistronic mRNA). This allows coordinated expression of genes involved in a common pathway.
5. Highlight the regulatory differences: In an inducible operon, the repressor protein is active by default and binds to the operator to block transcription until the inducer molecule inactivates the repressor. In a repressible operon, the repressor protein is inactive by default and requires a corepressor molecule to bind to the operator and inhibit transcription.

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 can be functionally related.

Inducible Operon

An inducible operon is typically off and can be turned on in response to an inducer molecule. This type of operon, such as the lac operon in E. coli, 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 and can be turned off by a corepressor molecule. An example is the trp operon, which regulates the synthesis of tryptophan. When tryptophan levels are high, it binds to the repressor, activating it and blocking transcription of the operon, thus preventing the unnecessary production of tryptophan.