Lecture 14 - Overview of eukaryotic gene expression Flashcards
How many genes do E.coli and humans ghve?
E.coli
~4000
Humans
~27000
Extra DNA in eukaryotes contains a lot of regulatory info
What structures in the eukaryotic genome are used to specify which cells transcribe a gene?
-complx combinations of regulatory DNA elements (enhaners)
-change during embryo genesis e.g.
Even skipped
-expression in developing fly embryo is in 7 transmembrane stripes
-segmented embryo has eve expressed in alternate segments
What are the multiple control points for euakryotic gene expression?
- DNA packaging
- transcription
- RNA processing
- mRNA stability/targeted RNA degradation
- RNA export and localisation
- translation
- post-translational modification
- protein stability/degradation
What are the proportions of RNA that are rRNA, tRNA and mRNA?
rRNA = ~80% tRNA = ~15% mRNA = ~5%
Most RNA is non coding
How many multisubunit RNA polymerases do eukaryotes have and what are there specific functions?
3 RNA pol I (rRNA) RNA pol II (mRNA) -simplest structure (12 subunits) RNA pol III (tRNA) -most complex (17 subunits)
What is the distribution of genes in humans that are coding/noncoding?
~23000 protein encoding gene
~4000 noncoding genes
How does the organisation of eukaryotic genomiv material present a challenge for transcription?
- contained within nuclei in which DNA id densely packed in chromatin
- low accessibility (access to genes is sometime blocked by chromatin)
- access to genes is regulatd by enzymes that modify and remodel chromatin
What is required for RNA pol recruitment to genes?
- multiple transcription factirs
- different cell types have different combinations of transcription factors
What is the process of production of mature mRNA?
- Primary RNA transcript is transcribed from the template strand and as transcription continues the 5’ end is capped (imp for the efficiency of translation)
- endonuclease cleaves at the Poly(a) site
- Poly(A) polymerase (PAP) along with ATP polyadenylates the transcript to stabilise it (must happen quickly)
- RNA spicing to remove introns and produce mRNA
Outline an extreme example of how differential splicing offers considerable oppourtunity for regulation and diversification
Alterantive spilicing of drosophila Dscam RNA
-potential to produce huge protein diversity from a single gene
-12 variants of exon 4
-48 vairants of exon 6
33 variants of exon 9
2 variants of exon 17=> over 38000 possible Dscam isoforms-
What are miRNAs?
regulate mRNA stability and or translation
- short pieces of RNA 21 nucleotides long
- can bind to mRNA by sequence compliemtarity
What is nonsense-mediated decay?
-ensures that mRNAs with premature termination codons are eliminated as templates for translation
Difference between eukaryotic and prokaryotic ribosomes?
bigger in eukaryotes
- greater complexity in TF controlling the assembly and regulation of transcription
- 13 eukaryotic translation initation factors, only 3 in bacteria
What is the function of multiple post translational modifications and give an extreme example
To regulation the function of eukaryotic proteins e.g. p53 Undergoes -ubiquitination -phosphorylation -acetylation -glycosolyation -methylation -neddylation -sumolation