Gene Expression Regulation II Flashcards
List 3 characteristics of gene expression regulation in eukaryotes
Gene regulatory proteins can act from a v.large distance from their promoters, RNA polymerase II doesn’t bind to promoter spontaneous it needs promoters (general transcription factors), and there is specific packaging of DNA(into chromatin)
Transcriptional activators bind to? Transcriptional repressors bind to ? They are capable of?
- enhancers
- silencers
- they can act at a great distance, they can be localized up and down stream, they can act independently to their orientation
How do transcriptional activators work
They can act directly on transcriptional machinery(by increasing the affinity of RNA polymerase for the promoter and facilitating promoter clearance) or change chromatin structure around the promoter(by recruiting additional proteins or controlling the open/close state of chromatin)
What is transcriptional synergy
It is the effect of the binding of many transcription factors to the mediator resulting in many more transcribed sequnces
How can you control the state of chromatin?
The promoter is very near the TATA box, a gene activator protein attracts a chromatin remodelling complex and this makes the promoter more accessible for the RNA polymerase II, they can also change histones with other histomes that promote transcription, and recruit histones modifying enzymes (histones acetyl transferases) that promote gene expression
How do transcriptional repressors work
They can act on chromatin (form heterochromatin), and they can act locally (repress a specific gene)
What are some characteristics of transcriptional repressors
There is no direct competition for the promoter, the binding sites of activators and repressors are v.close so if one is bound the other cannot, if the both the repressor and activator are bound then the repressor can block the activator site of the activator,
How do transcriptional repressors work
They can recruit chromatin remodling complexes that help condensation of DNA, and have histones deacytylase
What are transcription foci
Are areas in the nucleus where gene expression is v.high, this is called a transcription factory such as the nucleolus, producing rRNA, here are the nucleoplasmic factories
What are insulators
They are elements that delimit an area of a gene that must be expressed, inhibit the spread of heterochromatin, block enhancers elements when They are between enhancer and promoter
What are epigenetic processes
They do not change sequences of bases but they affect structure of DNA, include processes like DNA methylation, histones modification, RNA mediated phenomena
How does DNA methylation occur
It is catalysed by DNA methyl transferase and it uses the methyl group of an intermediate called S-adenosylmethionine and releases it as S-adenosylmonocystine
Detail CpG islands
Are regions in the genome where the frequency of CG are normal whereas everywhere else CG is very low, they have become CpT, they are unmethylated and surround the promoter of house keeping genes, in order to have a CpT a germ line mutation must occur. there are 20000 CG islands, they are mostly on the 5’ end
How is methylation passed on
When DNA is replicated you have a Hemimethylated situation where one strand is methylated(parent) and one strand isn’t, now maintenance methylases add methyl groups to the new strand as they recognise the Hemimethylated sequences,
What are de novo methylases (de novo methyltransferases)
When a gene that used to be expressed need no longer be transcribed we use de novo methylases to methylate/inactive them
