L9 - transcription Flashcards
differences between DNA and RNA
- DNA double stranded RNA single stranded
- DNA has a H instead of OH on 2 carbon
- RNA replaces T with U
what type of RNA leaves nucleus to be translated
mRNA
what is mRNA
copied from DNA in nucleus (transcription)
encodes protein
what is rRNA
structural and enzymatic component of ribosome
what is tRNA
delivers AAs to ribosome
what type of polymerase is involved in transcription and translation?
RNA pol
define transcription
production of mRNA from DNA
what are the 3 steps of transcription (in prokaryotes)
initiation
elongation
termination
what are the promoter sequences in prokaryotes and what position are they?
- pribnow box (-10)
2. -35
what are the functions of the promoter recognition sequences
align RNA pol to the transcription start site (via sigma factor)
what do promoter recognition sequences often consist of and why?
T and A sequence
easier to separate
function of sigma factor
recognises the -35 ad -10 promoter and binds them
then recruits the RNA pol in correct space
why is sigma factor needed
RNA pol isnt specific so can bind to any region of DNA, sigma factor directs it to the transcription start site
what unwinds the DNA during transcription?
RNA pol
describe initiation
binding of sigma factor and RNA pol
describe process of elongation
- RNA pol unwinds DNA as it moves
- RNA pol complimentary base pairs NTPs to template strand
- sigma factor dissociates after first few nucleotides
what provides energy for elongation process of transcription
PPi hydrolysis
describe process of rho independent termination
- mRNA transcript G-C rich stem loop sequence
- reduces binding of mRNA to DNA and ‘pulls’ it away
- after is a A-U rich sequence (easier to pull apart)
describe process of rho dependant termination
- rho protein follows behind DNA pol unwinding the newly synthesised RNA from the DNA strand
- DNA pol pauses at certain sequences (eg G-C rich harder to unwind)
- rho can catch up to DNA pol and terminate transcription
what are the differences between prokaryote transcription and eukaryote transcription
- eukaryotic has 3 RNA pols
what does RNA pol 1 in E synthesise
rRNA
describe structure of RNA pol 2
contains a C terminal domain tail
what does RNA pol 2 in E synthesise
mRNA and snRNA
what does RNA pol 3 in E synthesise
5s RNA and tRNA
what is pre-mRNA/ hnRNA
the mRNA as soon as it has been transcribed
prior to processing
what is the function of the CTD tail of DNA pol 2
co-transcriptional processing of pre-mRNA by :
- capping
- polyadenylation
- splicing
describe process of capping
7 methyl guanosine cap formed at 5’ end of mRNA (looks like upside down nucleotide triphosphate)
function of capping
protects end from degradation
roles in export from nucleus
roles in translation
describe process of polyadenylation
enzyme adds multiple As to 3’ end of mRNA
not encoded in DNA
function of polyadenylation
protects end from degradation
roles in export from nucleus
roles in translation
are exons or introns expressed
EXons
EXpressed
what is splicing
removal of introns by splicosome
what is alternative splicing
the process of splicing different combinations of exons as well as introns to give variation in protein products
describe the sections of transcribed RNA
Tscription start–5’UTR–protein coding region–3’ UTR
