Repressible operon

Definition

A repressible operon is a type of genetic regulatory system in prokaryotes that is typically on but can be turned off in response to the presence of specific molecules, often end products of a metabolic pathway. This system allows cells to conserve energy and resources by preventing the synthesis of certain proteins when they are not needed, which is crucial for efficient gene regulation in response to environmental changes.

5 Must Know Facts For Your Next Test

1. Repressible operons are often involved in anabolic pathways, where the end product can inhibit the expression of genes required for its own synthesis.
2. The classic example of a repressible operon is the tryptophan operon in E. coli, where tryptophan acts as a corepressor that binds to the repressor protein, enabling it to bind to the operator and block transcription.
3. In a repressible operon, when the concentration of the end product is high, the operon is repressed, leading to decreased production of enzymes necessary for its synthesis.
4. Repressible operons demonstrate negative regulation, contrasting with inducible operons that show positive regulation under specific conditions.
5. This regulatory mechanism plays a critical role in cellular metabolism by allowing prokaryotes to adapt their gene expression based on nutrient availability.

Review Questions

• How do repressible operons function at a molecular level to regulate gene expression?
  • Repressible operons function through a mechanism where a repressor protein binds to an operator sequence in the DNA, preventing RNA polymerase from transcribing downstream genes. When an end product, such as tryptophan, accumulates, it acts as a corepressor by binding to the repressor protein. This binding enhances the repressor's ability to attach to the operator, effectively blocking transcription and stopping further synthesis of enzymes involved in producing that end product.
• Compare and contrast repressible and inducible operons in terms of their regulatory mechanisms and examples.
  • Repressible operons are typically active and can be turned off by the presence of specific metabolites, like in the case of the tryptophan operon. In contrast, inducible operons are usually inactive and can be activated by an inducer molecule, such as lactose in the lactose operon. Both types serve crucial roles in regulating metabolic pathways; however, they operate under different conditions—repressible operons conserve resources when products are plentiful, while inducible operons respond to substrate availability.
• Evaluate the significance of repressible operons in prokaryotic gene regulation and their impact on cellular metabolism.
  • Repressible operons are significant in prokaryotic gene regulation as they provide an efficient way for bacteria to control metabolic processes based on environmental nutrient levels. By allowing genes involved in biosynthetic pathways to be turned off when their products are abundant, cells conserve energy and raw materials. This adaptability not only enhances survival in fluctuating environments but also illustrates a sophisticated level of control over gene expression that is essential for cellular efficiency and resource management.

Related terms

operon: A functional unit of genomic DNA that consists of a group of genes regulated together, allowing for coordinated expression.

inducible operon:

An operon that is usually off but can be turned on by the presence of an inducer molecule, facilitating the expression of genes in response to specific signals.

transcription:

The process of synthesizing RNA from a DNA template, which is a key step in gene expression.