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What is part I of the histone code hypnothesis?
Histone modifications can have remote effects on other histones.
What are the two types of Repression?
- Histone Stabillizing
- Nucleosome Blocking
Describe Repression by Nucleosome Blocking.
- A Nucleosome sits atop the promotor region, blocking transcription.
- Only after removal of the Nucleosome can transcription occur.
- An activator is required to remove the nucleosome and promote transcription.
Describe Histone Stabillized Repression.
- Histones and Nucleosomes are bound to the DNA but on the promotor.
- Transcription does not occur because Histone H1 stabillizes the Nucleosomes flanking the promotor.
- Removal of Histone H1 (Nucleosomes remain) gives "Competant" transcription.
- Binding of an Activator gives "Active" transcription.
Which is removed first, Histones or Nucleosomes?
Histones, then Nucleosomes.
What Histone does Histone repression use?
What is Chromatin Remodelling?
Selectively altering chromatin at defined locations.
What are the two types of Chromatin Remodelling?
- Nucleosome Displacement (Removal)
- Nucleosome Repositioning (Octamer Sliding)
How does the Swi/SNF complex work?
- Binds with BRG-1
- Uses ATP to "loosen" chromatin structure
- Binds to Octamer
What does Swi/SNF do?
Converts a Silent Gene to an Active Gene
What is the Chromatin Remodelling complex?
What is the Second Part of the Histone Code Hypothesis?
Different Modifications are read differently, allowing for complex regulation of Structure and Transcription.
Can Nucleosomes be present at sites of high Transcription?
How does elongation deal with Nucleosomes?
The FACT complex (associated with polymerase) remodels DNA ahead and behind the active site.
What does FACT stand for?
Facilitates Chromatin Transcription