1.3 - Regulation of Gene Expression in Eukaryotes Flashcards
What is the difference between transcription and translation in prokaryotes and eukaryotes?
- uncoupled in eukaryotes as separated in the nuclear membrane
- coupled in prokaryotes as no membrane to separate them
Explain mRNA processing in eukaryotes
- 5’ end capping
- 3’ end polyadenylation
- splicing
What is 5’ end capping?
addition of altered nucleotide onto the 5’ end of the primary transcript that stops the strand being recognised by nucleases
What is 3’ end polyadenylation?
- sequence at the end of gene which is recognised by specific nucleases and cleaved
- adenines are then added
- proteins bind to polyA tail and 5’ cap
- protects the ends of mRNA
- polyA tail gets shorter in translation as nucleases degrade it
- proteins will no longer bind to poly A tail
- mRNA looses protection
Is eukaryotic DNA monocistronic or polycistronic?
monocistronic
What does it mean if DNA is monocistronic?
every gene has its own promoter and every mRNA codes for its own protein
How many RNA polymerases are there in prokaryotes and eukaryotes?
prokaryotes - 1
eukaryotes - 3
What are the 3 RNA polymerase in prokaryotes?
Pol I - transcribe structural RNA
Pol II - transcribe all of the protein code in genes
Pol III - transcribe structural RNA
What is the difference in promoters between prokaryotes and eukaryotes?
- in eukaryotes there is extended promoters up to 1000 bps from core promoter
explain transcription regulation
- RNA Pol II binds to TATA box in both activated and inactive states
- promoter proximal elements bind proteins to the RNA Pol II
- sequences called enhancers or silencers bind either activators or repressors and then bind this to the RNA Pol II
What is the structure of eukaryotic promoter?
Promoter proximal elements
- GC - rich box - -200bp
- CCAAT - -100bp
Promoter
- TATA - -30bp
What is euchromatin?
open form of chromatin accessible to TFs
What is heterochromatin?
highly packed chromatin poorly accessible to TFs
Explain genes in heterochromatin and euchromatin
Heterochromatin
- silenced
- TFs cannot get through
Euchromatin
- active
- TFs can access
What is spliceosome?
- ribonucleoprotein complex (made of RNA and proteins)
- recognised the 5’ and 3’ end of exons
- brings them together
How does the spliceosome do alternative splicing?
- brings the 3’ end of one intron to the 5’ end of another
What is the role of alternative mRNA spacing in sex determination of drosophila?
- pre-RNA == double sex - has everything for both sexes
- DNA binding domain is created which is the same in both sexes (exons 1, 2, 3)
- remain exons are spliced in a combination that makes 2 different repressors(f = 4, M = 5, 6)
- in females - represses male genes
- in males - represses female genes
Why are post-translational modifications important?
- allows quick response to environmental signals - don’t wait for transcription and translation
- most are reversible
- energy saving
Which enzyme phosphorylates a protein?
kinase
Which enzyme dephosphorylates a protein?
phosphatase
What is the role of protein kinases?
- transfer a phosphate group using ATP to serine, threonine or tyrosine
- as phosphate needs OH acceptor
How does phosphorylation regulate protein-protein interactions?
- protein A interacts with protein B
- protein A is phosphorylates
- protein A will no longer interact with protein B - may be due to size or charge
- protein A does not interact with protein C
- protein A is phosphorylates
- protein A interacts with protein C - may be due to shape or charge
What is needed for the increase and decrease of cyclin-CDKs?
increase - transcriptional activation
decrease - protein degradation
How do cells degrade proteins that regulate the cell cycle?
- ubiquitin is added to protein’s lysines that are to be degraded
- more ubiquitin can be attached to the first lysine
- proteasome then recognises ubiquitin and degrades the protein
