Transcription factor
A protein that binds DNA near a gene and helps or blocks RNA polymerase. Activators raise transcription. Repressors lower it. Enhancers are DNA sites where activators bind, often far from the gene.
Last updated
Analogy
Volume knobs and dimmer switches for each gene.
In practice
A liver cell and a nerve cell have the same DNA, but different transcription factors make different genes active.
Practice
Flashcards
- What is the difference between an activator and a repressor?An activator raises transcription. A repressor lowers or blocks it.
Interview questions
- Explain how the lac operon is regulated and why this benefits E. coli.
- Repressor blocks genes without lactose
- Lactose binds repressor and it releases DNA
- Genes for lactose enzymes switched on
- Saves energy when lactose is absent
Questions people ask
Why do different cells have different genes active?
Every cell holds the same DNA, but each cell type makes a different set of transcription factors. These proteins turn some genes on and others off. This is how one fertilised egg can become muscle, nerve, skin and many other cell types.
What is an enhancer?
An enhancer is a stretch of DNA that increases the transcription of a gene. Activator proteins bind to it, and the DNA loops so the bound proteins touch the machinery at the promoter. Enhancers can sit thousands of base pairs away, and they often work only in certain tissues.