Control of Eukaryotic Gene Expression Flashcards
Examples of gene expression regulation points
transcriptional control, RNA processing, translational control & protein controls
What is the function of RNA polymerase III
transcribes ALL tRNA genes, rRNAs and other small RNA genes
What is the function of RNA polymerase I
transcribes genes encoding ribosomal RNA genes, protein synthesis
What is the function of RNA polymerase II
transcribes ALL protein coding genes and some non-protein coding genes
What do house keeping genes encode
RNAs or proteins required for universal cell functions
TRUE or FALSE - protein coding genes are regulated
FALSE
TRUE or FALSE - protein coding genes are continually on
TRUE
What are the functions of protein coding genes?
Metabolic pathways, nucleic acid synthesis, protein synthesis, cell survival, DNA repair
What does in situ hybridisation reveal
gene transcription patterns in tissues and whole organisms
What is the function of differentially expressed protein coding genes
make cells different to one another
When are differentially expressed protein coding genes regulated
transcriptional level
What do differentially expressed protein coding genes code for
cell adhesion proteins, ion channels, cell surface receptors, transcription factors
How is transcriptional control exerted?
binding of trans acting factor proteins to specific cis acting DNA sequences next to gene
What does initiation of transcript synthesis require?
physical interactions between trans-acting factors, RNA polymerase & transcription factors
Where are general transcription factors ALWAYS present
house keeping genes
Where is the TATA box found
every Eukaryotic promoter
What is the TATA box
DNA sequence found in the promoter
What is the function of the TATA box
forms transcription initiation complex
Where does the TATA box lie in relation to transcription
upstream, at start of the gene
What does transcriptional activation require in vivo
other transcription activators, auxiliary proteins
What is the function of Auxiliary proteins
stabilise transcription initiation complex, dictate gene transcription
What does cycloidea transcription factor promote
bilateral symmetry
What is Gli3 important for
limb patterning on AP axis
What does loss of Gli3 lead to
extra digit
What is Gli3
sequence specific DNA binding protein
Competition between what regulates transcription
transcriptional activators and repressors for RNA polymerase
Describe the transcriptional factor protein structure
modular, sequence specific DNA binding domain, regulatory domain
What are eukaryotic transcriptional repressors
sequence specific DNA binding proteins
How do transcriptional repressors work
mask activation surface, or direct interaction with general transcription factors
Describe steroid hormones
highly specific activating ligands
Describe steroid hormones structure
hydrophobic
How do steroid hormones move through the cell membrane
pass directly through
Examples of steroid hormones
cortisol, estradiol, testosterone, thyroxine
What to steroid hormones bind to
nuclear hormone receptors
What to cis-acting DNA enhancer elements bind to
tissue-specific transcription activators
What do transcriptional repressors interfere with
transcription activator function
Describe chromatin
organised, supercoiled nucleoprotein fibres
Where is chromatin NOT present
prokaryotes
What do structural changes to chromatin affect
gene transcription
Why do structural changes to chromatin affect gene transcription
can restrict accessibility of transcription factors
What is chromatin comprised of
nucleosomes
What is the function of chromatin
allow for packing of DNA, prevents transcription factors from finding binding sites
What do chromatin remodelling factors do
move histones along DNA - open and close access to DNA sequences
What is the function of chromatin remodelling factors
facilitate transcription factor access to target genes
What does the covalent modification of DNA require
enzymes
What happens to the regions of chromatin that are covalently modified
flagged to direct repressors or activators to target DNA sequences
Where does histone H1 bind
edge of nucleosome
What is the function of histone H1
stabilises nucleosome structure, limits accessibility of genes for transcription
What is acetylation
covalent modification
Where does acetylation take place
lysine in N-terminals amino acids within histones
What is the function of acetylated lysines ?
Act as flags to recruit chromatin remodellers to open up chromatin
What does acetylation signal to chromatin remodellers
to remove histone H1
Where does methylation occur (chromatin)
cytosine bases in CpG dinucleotides
What is methylation a hallmark of?
transcriptionally inactive chromatin
Where are CpG islands often found?
start of the gene
What is the function of methylation of genes
switch genes OFF
What does methylation act as a flag for
repressors
Describe germline methylation
sex specific methylation, only occurs in gamete production
What is the function of RNA splicing
removal of introns and ligation of exons
What is RNA splicing important for in Drosophila
sex determination
What is the 5’ cap on mRNAs required for
translation initiation on circularised polyadenylated mRNAs
What is polyadenylation required for
form circular structure
What is the function of ferritin
store iron
What is ferritin
protein
What is translation of mRNA encoding ferritin regulated by
positively regulated by free iron concentration
What happens to ferritin in low iron concentrations
aconitase binds tightly to ferritin and blocks translation by blocking the ribosomes
What happens to ferritin in high concentrations of iron
aconitase dissociates from ferritin mRNA and translation occurs
What helps to package DNA
chromatin remodelling factors & covalent modifications
What iron concentration inhibits binding of aconitase to ferritin mRNA
high iron concentrations
What is Gli3 involved with
hh signalling pathway
What is the function of Gli3
regulate transcription of hh genes
