Topic 13.2: Transcription Flashcards
what does transcription do
DNA -> mRNA
what does gene expression in transcription require
template - DNA
enzymes - RNA polymerase
substrates - NTPs
3 steps - initiation, elongation, termination
what are some key features of transciption
catalysed by RNA polymerase
hydrolysis of PPi by pyrophosphate drives reaction to form NTP
double stranded DNA template required and read from 3 to 5 end
NTP’s and Mg2+ needed
synthesis from 5 to 3 prime end
how is rRNA made
by RNA polymerase I
how is mRNA made
by RNA polymerase II
how is tRNA made
by RNA polymerase III
how many RNA polymerase are there in eukaryotes
3 in nucleus, 1 in mitochondria, 2 in chloroplasts
how many RNA polymerase are there in prokaryotes
1 copy: RNAP = bacterial RNA polymerase
the core enzyme of RNAP has 5 subunits - make random RNA
the holoenzyme has 6 subunit (core + sigma) - for the sigma binds to specific regions on the promoter to make specific mRNA
what is present in the promoter region and what occurs during transcription intiation
transciption factors
Transcription factors recognize the promoter. RNA polymerase II then binds and forms the transcription initiation complex.
in what direction to transcription factors binds
binding is directionally towards the TATA box
recognised by transcription factor in a directional way, so the polarity is important as otherwise transcriptional factor binds in the wrong direction and directionally bind the promoter
Transcription factors bind
to upstream sequences
how is gene expression regulated
the way transcipton factors bind to promoter controlls when a gene is expressed
what are the steps involved in transcription initiation
- TF binds to TATA
- more TF’s bind to upstream sequences
- RNA polymerase is recruited
- unwinding of DNA helix
- formation of a transcription bubble (17 base pairs)
- transcription initiates, directionally 5 to 3 end
why is only one of the double DNA strands being used as a template
as making RNA which is single stranded
what is involved in transcription elongation
- RNA synthesis from 5 to 3
- template strand is read 3 to 5
- single stranded RNA molecule is made
- as transcription bubble advance, DNA helix reforms behind it
what is being used as a template, coding and coding strand
DNA template is transcribed
- will be complementray to new RNA strand
- will be complementary to other DNA strand
thus, the non transcribed DNA strand is also the coding strand (same sequence of new RNA) and the transcribed DNA strand is the non coding strand/template strand
what are some features of transcription termination
sequence dependent
results in primary RNA molecule
RNA processing needed to proudce mature RNA
what is RNA processing
post transcriptional modification
what is involved in RNA processing in rRNA and tRNA
chemical modifications and cleavage
what is involved in RNA processing in mRNA
eukaryotes - capping (5 prime), slicing (middle) and tailing (3 prime)
what is capping
a 5 prime Cap is being added and a methylaed G linked molecule added, which forms a 5-5 prime linkage
- provides protection and plays role in translation
what is tailimg
lots of A being added to 3 prime end
- for protection and regulation
what is splicing
highly accurate removal of introns and exons joined together
by spliceosomes
mature mRNA contains open reading frame plus 5 prime and 3 prime untranslated regions
how many exons are there
always one more than intron
splicing errors can cause
disease
how is splicing used in regulation
can make different polypeptides from the same gene by splicing
Chronological ‘replication order’
Origin of replication recognition Unwinding of DNA helix RNA primers generated DNA elongation from 5 to 3 Further helicase and primase activity DNA polymerase catalyse leading strand extension Ozaki fragments joined by ligase Replication forks meet
