which statement s about repressible operons is are correct

Charlotte

2 min read

·

27-02-2025

1

0

Share

Which Statements About Repressible Operons Are Correct?

Repressible operons are a fascinating aspect of gene regulation in bacteria. Understanding how they work is key to grasping the intricacies of prokaryotic gene expression. This article will delve into the characteristics of repressible operons, clarifying which statements about them are accurate and which are not. We'll explore the mechanisms involved and dispel common misconceptions.

What is a Repressible Operon?

A repressible operon is a type of operon—a cluster of genes transcribed together—where gene expression is usually on but can be turned off. This contrasts with inducible operons, where gene expression is usually off and is turned on by an inducer. The key difference lies in the default state of the operon: active for repressible, inactive for inducible.

The core components of a repressible operon are:

• Structural Genes: These genes code for enzymes involved in a specific metabolic pathway.
• Promoter: The region where RNA polymerase binds to initiate transcription.
• Operator: A short DNA sequence that acts as a binding site for a repressor protein.
• Repressor Protein: A protein that binds to the operator, preventing RNA polymerase from transcribing the structural genes.
• Corepressor: A molecule that binds to the repressor protein, changing its shape and allowing it to bind to the operator.

Analyzing Statements About Repressible Operons

Let's examine some common statements about repressible operons and determine their accuracy:

Statement 1: Repressible operons are usually "on" in the absence of a corepressor.

TRUE. In the absence of the corepressor, the repressor protein is inactive. It cannot bind to the operator, allowing RNA polymerase to transcribe the structural genes. The pathway remains active.

Statement 2: The corepressor binds directly to the promoter region.

FALSE. The corepressor binds to the repressor protein, not directly to the promoter. This binding alters the repressor's conformation, enabling it to bind to the operator.

Statement 3: Repressible operons are involved in anabolic pathways.

TRUE. Repressible operons typically regulate anabolic pathways – pathways that synthesize molecules. When the end product of the pathway is abundant (acts as a corepressor), the operon is repressed, preventing further synthesis. This prevents wasteful production.

Statement 4: The repressor protein is always active, even in the absence of a corepressor.

FALSE. This describes a constitutive operon, always “on.” In a repressible operon, the repressor is only active after binding with the corepressor.

Statement 5: The trp operon is an example of a repressible operon.

TRUE. The trp operon, responsible for tryptophan biosynthesis, is a classic example of a repressible operon. When tryptophan (the end product) is abundant, it acts as a corepressor, repressing the operon.

Statement 6: Inducible operons and repressible operons are regulated in the same way.

FALSE. They are regulated differently. Inducible operons are usually off and turned on by an inducer molecule, whereas repressible operons are usually on and turned off by a corepressor.

Examples of Repressible Operons

Besides the trp operon mentioned above, other examples of repressible operons include those involved in the biosynthesis of:

• Arginine: The arg operon is repressed when arginine levels are high.
• Histidine: The his operon is similarly regulated by histidine levels.

These operons showcase the elegant feedback mechanisms that bacteria use to efficiently manage resource allocation.

Conclusion

Understanding the intricacies of repressible operons is vital for grasping the sophisticated control mechanisms within bacterial cells. By clarifying the accurate statements about their function and distinguishing them from other operon types, we gain a deeper appreciation of gene regulation in prokaryotes. The ability to regulate gene expression allows bacteria to adapt effectively to changes in their environment, ensuring survival and efficient resource utilization. Remember that the default state of a repressible operon is "on", and its regulation is primarily driven by the presence or absence of a corepressor molecule.