Gene expression Flashcards
rRNA
> 80% of total RNA
- few kinds, many copies
- small and large rRNAs
- highly conserved
tRNA
less than 15%
small
each one dedicated to one of 20 amino acids
mRNA
2-5% of total RNA
what do you need for transcription
making RNA
template- DNA
enzyme- RNA polymerase
substrate- NTPs- ribonucleotides
how is RNA synthesised
5’ to 3’
DNA read 3’ to 5’
what is needed for promoter binding
transcription factors
Trancription initiation
- transcription factor binds promoter
- binding is directional on TATA box
- RNA polymerase recruited
- unwinding DNA helix
- formation of a transcription bubble
- transcription initiates, directionally 5’-3’
what is the TATA box
specific sequence on all promotor sequences
transcription elongation
- RNA synthesis from 5’ - 3’
- template strand is read 3’ - 5’
- single stranded RNA molecule is made
- only one DNA strand is used as a template
-as transcription bubble advances, DNA helix reforms behind it
coding strand
non-transcribed DNA strand
non-coding starnd
transcribed DNA strand
transcription termination
- sequence-dependant, other factors involved
- results in a primary RNA molecule
- RNA processing needed to produce mature RNA
RNA processing
- post-translational modifications
- rRNA and tRNA
- chemical modicfications and cleavage
- mRNA
- eukaryotes|: capping, splicing and tailing
Capping
5’ cap
methylated-g linked 5’-‘5’
provides protection
plays role in translation
tailing
3’ poly A tail
for protection and reglation
splicing
highly accurate removal of introns
exons joined together by splicosomes- ribonucleoprotein complex
mature mRNA contains ORF- open reading frame plus 5’ UTR and 3’UTR (untranslated region)
splicing errors can cause disease
what is the initiation codon in translation
AUG
What are the stop codons
UAA
UAG
UGA
What do u need for translation
template- mRNA
enzyme- rRNA in ribosomes
substrates- activated amino acids
charged tRNA
initiation factors, elongation factors, release factors and energy
what is a charged tRNA
a tRNA with an amino acid attached
Translation- initiation
- recognition of cap by tRNA- Met
- recognition of AUG by anticodon of ‘inititaion complex’
- Initiation factors involved
- recruitment of large ribosomal subunit (60S)
- assembly of functional ribosome
translation- elongation
- binding of aminoacyl-tRNA in A-site
- peptide bond formation catalysed by peptidyltransferase
- translocation- ribosome moves one codon from 5’ to 3’
- uncharged tRNA IN E SITE
- elongation factors involved
- peptidyl-tRNA in P-site and empty A site
translation termination
- peptidyl-tRNA in P site and empty A site with stopcodon
- binding of Release factor
- RF recognises stop codon
- hydrolysis resulting free peptide and uncharged tRNA in P-site
- dissociation of ribosome into subunits
