Repressor

Definition

A repressor is a type of protein that inhibits gene expression by binding to specific DNA sequences, preventing the transcription of genes into RNA. By doing so, repressors play a crucial role in regulating cellular processes, ensuring that genes are expressed only when needed and helping maintain cellular homeostasis.

5 Must Know Facts For Your Next Test

1. Repressors are crucial for the regulation of operons, which are clusters of genes controlled by a single promoter in prokaryotes.
2. When a repressor binds to the operator, it physically blocks RNA polymerase from transcribing the downstream genes.
3. Some repressors require co-repressors, which are molecules that enhance the repressor's ability to bind to the operator and inhibit transcription.
4. Repressors can be involved in both negative feedback loops and complex regulatory networks within the cell.
5. The presence or absence of specific inducers can determine whether a repressor is active or inactive, thus modulating gene expression based on environmental conditions.

Review Questions

• How do repressors influence gene expression and what is their role in an operon?
  • Repressors influence gene expression by binding to the operator region of an operon, blocking RNA polymerase from accessing the promoter. This inhibition prevents the transcription of downstream genes, effectively silencing them. The ability of repressors to control gene expression is essential for cellular regulation, allowing organisms to adapt to changing conditions by turning genes on or off as needed.
• Discuss the mechanisms through which repressors can be activated or inactivated.
  • Repressors can be activated or inactivated through interactions with small molecules known as inducers. When an inducer binds to a repressor, it often causes a conformational change that prevents the repressor from binding to the operator. This allows RNA polymerase access to the promoter and enables transcription. Conversely, co-repressors can enhance a repressor's function by promoting its binding to the operator, thus inhibiting transcription more effectively.
• Evaluate the importance of repressors in maintaining cellular homeostasis and how disruptions in their function might lead to disease.
  • Repressors are vital for maintaining cellular homeostasis by ensuring that genes are expressed only when necessary. They help fine-tune metabolic pathways and responses to environmental changes. If repressors malfunction or are incorrectly regulated, it can lead to uncontrolled gene expression, contributing to diseases such as cancer where growth-control genes are not properly inhibited. Understanding repressors' roles offers insights into potential therapeutic targets for restoring normal cellular function.

Related terms

Promoter: A region of DNA located upstream of a gene where RNA polymerase binds to initiate transcription.

Operator: A segment of DNA within an operon that a repressor can bind to, thereby controlling access to the promoter and regulating transcription.

Inducer: A small molecule that can bind to a repressor and cause it to change shape, thus preventing it from binding to the operator and allowing gene transcription to occur.