Transcriptional Regulation Flashcards
Describe transcriptional regulation?
Gene expression beings at the promoter; a sequence of DNA adjacent to the gene where transcription factors bind and RNA polymerase is recruited to initiate transcription
What are the two types of regulatory proteins may bind DNA?
Repressor proteins and activator proteins
Explain regulation of gene expression in prokaryotes
Core promoter elements variants recognised and bound by specific sigma factors; strong promoters conform to the consensus sequence and initiate transcription frequently
What are the 3 proteins involved in the uptake and metabolism of lactose?
beta-galactoside permease ( carrier protein that moves sugar into the cell); beta-galactosidase (an enzyme that hydrolyses lactose); beta-galactoside transacetylase (transfers acetyl groups to certain b-galactosides)
What are the two ways to regulate a metabolic pathway?
allosteric regulation of enzyme-catalysed reactions allows rapid fine-tuning or regulation of gene expression
What is an operon?
It is a cluster of genes with a single promoter and transcribed together in a single mRNA, within a prokaryote
What does an operon consist of?
A promoter; two or more structural genes; an operators (short stretch of DNA between promoter and structural genes)
What are the 3 ways transcription is regulated in prokaryotes?
An inducible operon regulated by a repressor protein (default is off); a repressible operon regulated by a repressor protein (default is on); an operon regulated by an activator protein (default is off)
What do inducible operons control?
Catabolic pathways
What do repressor systems control?
Anabolic pathways
If an operon is regulated by an activator protein, what happens?
It increases transcription through positive control
Name the 10 points of regulation of gene expression in Eukaryotes
Must be regulated to ensure proper timing of protein production; can occur at multiple points; remodelling of chromatin for transcription; transcriptional regulation; pre-mRNA splicing; transport of the mRNA; mRNA stability; translational control at the ribosome; post-translational modification of proteins; protein degradation
What is chromatin remodelling?
It is the alteration of chromatin structure
What charge is the amino acid tail on histones at its N terminus?
Positively charged
How are histone acetyltransferases able to change the charge of their tails?
By adding acetyl groups to lysine residues
What does changing the charge of the tails do?
It opens up nucleosomes; increases DNA accessibility; facilitates transcription factor binding and recruitment of chromatin remodelers; activates transcription
What are the possible mechanisms for increased local access?
Nucleosome sliding; nucleosome displacement; partial histone displacement; replacement of octamer subunit with histone variants
What are the two kinds of chromatins that are visible during interphase?
Euchromatin and heterochromatin
What does euchromatin do?
It actively transcribes genes
What is heterochromatin?
It contains genes that are not transcribed
What determines the levels of transcription (promoter strength)?
The efficiency of binding of GTFs to the core promoter DNA sequences
Describe regulation of transcription in eukaryotes.
General transcription factors binding the core promoter to recruit RNA polymerase.
Transcriptional activator or repressor proteins bind to the DNA regulatory elements.
General transcriptional factors binding the core DNA promoter (starting with TFIID) to recruit RNA polymerase.
What is the tata-box?
It is a DNA sequence that indicates where a genetic sequence can be read and decoded and is a type of promoter sequence, which specifies to other molecules where transcription begins.
What helps repress or enhance the transcription levels?
Transcriptional activator and repressor proteins
What are the four DNA binding domains?
Helix-turn-helix
Leucine zipper
Zinc finger
Helix-loop-helix
What does the activation/repression domain do?
It interacts with target proteins
What is DBD?
DNA binding domains
What are the 3 things DBD must have?
Must fit into major or minor groove
Must have amino acids that can protect into interior of double helix
Must have amino acids that can bond with interior bases (recognition helix)
What is cooperative binding?
The arrangement of transcription factor binding sites that twp different transcription factors can interact, stabilising each other’s binding to the DNA
How can gene expression be regulated in prokaryotes?
Downregulation of transcription Hydrolysis of mRNA Prevent mRNA translation at the ribosome Degrade protein after its made Inhibit the function of protein Kinase can phosphorylate protein to alter functionality
Describe transcriptional regulation in prokaryotes
Gene expression begins at the promoter.
sequence of DNA adjacent to the gene where transcription factors bind and RNA polymerase is recruited to initiate transcription.
A repressor protein can bind to DNA and competes with RNA polymerase so the sigma factor cannot bind, blocking transcription.
What are core promoters bound by?
Specific sigma factors
What is the Holo-RNA polymerase?
It is a form of eukaryotic RNA polymerase II that is recruited to the promoters of protein-coding genes in living cells.
What 3 proteins are involved in the uptake and metabolism of lactose in prokaryotes?
beta-galactoside permease (carrier protein that moves sugar into cell)
beta-galactosidase (an enzyme that hydrolyses lactose)
beta-galactoside transacetylase (transfers acetyl groups to certain B-galactosides)
What are the three ways to control operon transcription?
An inducible operon regulated by a repressor protein
A repressibe operon regulated by a repressor protein
An operon regulated by an activator protein
Describe what happens when an inducible operon is regulated by a repressor protein
A repressor protein encoded by gene X prevents the transcription by binding to the operator. RNA polymerase cannot bind to the promoter, blocking transcription. An inducer can inactivate the repressor to allow the RNA polymerase to transcribe.
Key points for the regulation of gene expression in eukaryotes.
Transcription - transcriptional regulation, pre-mRNA splicing, transport of the mRNA from the nucleus to the cytoplasm
Translation - protein degradation, post-translational modification, translational control, mRNA stability
How is 2m of DNA packaged into the nucleus?
Wrapped around histone octamer twice and histone H1 further compacts this into tighter fibres
What is covalent modification?
Each histone has a positively charged amino tail at its N terminus. Histone acetyltransferases can change the tails charge by adding acetyl groups to lysine residues. This opens up the nucleosome and increases DNA accessibilty.
What are the mechanisms to increase access to DNA?
Nucleosome sliding; nucleosome displacement; partial histone displacement; replacement of octmer subunits with histone variants
