rna transcription Flashcards
transcription
rna synthesis from a dna template
what is the function of rna polymerase I
make rRNA
what is the function of rna polymerase II
makes protein encoding genes
what is the function of rna polymerase III
makes tRNA, small nuclear RNA & 5S rRNA
what is the function of topoisomerases?
cut DNA strand to release supercoils allowing DNA polymerase/RNA polymerase progression
TATA box
promoter element found 30 bp upstream of gene
TATA binding protein binds to it —–> bends DNA to facilitate RNA polymerase binding
important for all transcription
why is the addition of an RNA cap at the 5’ end necessary?
- stability
- binding of mRNA to ribosome
- initiation of translation
how is the 5’ cap synthesised?
- rna triphosphatase removes phosphate from 5’ end of mRNA
- guanyl transferase adds guananine in a 5’-5’ linkage = triphosphate bridge
- methyl transferase adds methyl group to guananine
why is the polyadenyation of 3’ end necessary?
- aids translation
- polyA tail = checkpoint before mRNA is exported out of nuclear pore
- stability
what does the spliceosome consist of?
snRNP = snRNA + >7 protein subunits
what is the polyA signal?
AAUAAA
CstF
promotes cleavage of mRNA at a site 10-30 nucleotides downstream of polyA signal
CPSF
promotes cleavage
stays attached as PAP adds As
PAP
adds up to 200 As to 3’ end then drops off
describe process of polyadenylation
- cstf and cpsf bind to c terminal domain on rna polymerase –> proteins recruited to site where polyA signal emerges
- proteins recognise polyA signal
- cleavage at a cleavage site 10-30 nucleotides downstream of polyA signal
- PAP adds As to 3’ end
- poly a binding proteins assemble onto polyA tail as it is synthesised
