Transcriptional Regulation - Eukaryotes Flashcards
How can eukaryotes regulate transcription?
Using repressors and activators and also chromatin remodelling
Where is the regulatory region of a eukaryotic gene?
Before the core promotor - where the transcription factors bind
What binds in the regulatory region of a gene?
Repressors and activators
What are 2 ways a transcriptional activator can increase transcription in eukaryotes?
Either directly by recruiting RNA polymerase or indirectly by recruiting general transcription factors
Is it general or specific transcription factors that are responsible for gene regulation?
Specific
What are regulatory sequences that are very far from the promotor called?
Enhancers
How are enhancers brought closer to the promotor that it is regulating?
Looping of the DNA
What binds to enhancers?
Specific transcription factors that increase transcription
What are insulators?
DNA sequences bound by proteins that block the function of enhancers
Say an enhancer is between two genes and is the same distance from both. What makes it regulate the gene it is supposed to regulate and not the other one?
An insulator will be between the enhancer and the gene it is not supposed to regulate. It will block the enhancer from looping to that gene, so it defines which genes are acted on by that enhancer
Does looser or tighter chromatin favour increased transcription?
Looser
Does tighter chromatin mean it is heterochromatin?
No, it is still referring to euchromatin that is slightly tighter or slightly looser. Transcription only happens in euchromatin
What are 3 general ways chromatin is loosened or tightened?
- Slide nucleosomes along the DNA
- Remove a nucleosome
- Squish nucleosomes together
What was the experiment that showed how chromatin remodelling can change gene expression over the course of development?
They used DNase I, which can’t any DNA that is bound to histones or that is more tightly packaged. Examined how susceptibility to DNase I changed over the development of a chick embryo in one embryonic globin gene and two adult globin genes. None of the genes got cut after 24 hours, only the embryonic gene got cut after 5 days, and only the adult genes got cut after 14 days. It didn’t get cut in cells where it wasn’t supposed to be expressed either
What is the chromatin remodelling complex?
Proteins that can reposition nucleosomes
What recruits the chromatin remodelling complex?
Transcriptional activators and repressors
What are histone tails?
Parts of the histone proteins that extend out of the nucleosome for higher levels of packaging
What are the 4 covalent modifications that can be made to histone tails to promote chromatin remodelling?
Acetylation, methylation, phosphorylation and ubiquination
What enzymes add acetyl groups to histone tails? Which enzymes remove them?
Acetyltransferases add them, deacetylases remove them
Does acetylation tend to promote more loosely or more tightly packed chromatin?
Looser
What enzymes add methyl groups to histone tails? Which enzymes remove them?
Added by methyltransferases, removed by demethylases
How do the histone tail modifications have meaning to other proteins?
They are read like a code and tell the chromatin remodelling complex whether to loosen or tighten the chromatin
Does methylation tend to promote more loosely or more tightly packed chromatin?
Depends on which amino acid it is attached to
How can DNA be modified to cause chromatin remodelling?
Methylation of cytosine bases
Does DNA methylation increase or repress transcription?
Represses it. Methylated DNA is more tightly packed
How does methylated DNA cause chromatin to become tighter?
It recruits histone tail deacetylases
What is the advantage of methylating DNA over methylating histone tails?
Stronger bond in DNA, which makes the repressed state stick around longer
What are the 3 mechanisms that cause chromatin remodelling?
- Direct recruitment of the chromatin remodelling complex
- Indirect recruitment through histone modification
- Indirect recruitment through DNA methylation
How does direct recruitment of the chromatin remodelling complex work?
An activator or repressor binds to a regulatory sequence. That recruits the chromatin remodelling complex and loosens or tightens the chromatin
How does indirect direct recruitment of the chromatin remodelling complex through histone modification work?
An activator or repressor binds to a regulatory sequence. That recruits a histone modifying enzyme which adds or removes modifications on the histone tails. The modifications recruit the chromatin remodelling complex and the chromatin becomes looser or tighter
How does indirect recruitment of the chromatin remodelling complex through DNA methylation work?
An activator or repressor binds to a regulatory sequence. That recruits DNA methyltransferase that methylates the DNA. The methylated DNA recruits a histone modifying enzyme that removes histone modifications. That recruits the chromatin remodelling complex which tightens the chromatin
How does coordinated regulation of gene networks occur in eukaryotes?
At the level of the transcription factors. They can be regulated by the same specific transcription factors
Do eukaryotes have operons?
No
