Gene expression Flashcards
What is a gene
unit of transcription
What is a promoter sequence
TATA box
name/ explain the steps involved in the initiation of transcription
promoter recognition
transcription initiation factors bind
RNA polymerase II recruited
Name/ explain the steps involved in the elongation of mRNA
DNA strand separated
3’ 5’ strand acts as template so that mRNA produced 5’ to 3’
Explain the steps involved in the termination of mRNA production
sequence dependent
specific endonuclease comes and cleaves mRNA a cleavage site
What prevents mRNA degradation? How are these added?
5’ cap 5’5 linkage made immediately
polyA tail on 3’ end added by poly A polymerase after termination of mRNA production
Why is the DNA sequence often much longer than the mature mRNA?
splicing occurs where introns are removed
What ribosomes and their subunits are present in prokaryotes?
30s and 50s
70 s ribosome
What ribosomes and their subunits are present in eukaryotes?
40s and 60s
80 s ribosomes
What RNA polymerase produces mRNA?
II
What RNA polymerase produces tRNA?
III
What RNA polymerase produces rRNA?
I
Explain the process of translation in simple terms
mRNA read 5’ to 3’
each codon= aa delivered by tRNA
polypeptide produced N–> C
Explain the structure of a tRNA molecule
Clover model
tRNA single stranded–> folded to form double stranded regions
H bonds form between antiparallel complementary sequences
bottom= anticodon
3’OH = amino acyl group added
How is amino acyl group added to tRNA?
At 3’ OH end
requires ATP and aminoacyl tRNA synthase
pyrophosphate released providing energy to drive reaction
What is always the start codon ?
AUG
Why is the genetic code described as degenerate?
every 3’ base in codon/ 5’ base in anticodon is in the wobble position meaning it is variable
as a result a single tRNA species recognise more than 1 codon
Degenerate means more than one thing means the same in this instance more than one codon codes for the same amino acid
Explain the process of initiation in translation
40s subunit GTP cap binding proteins initiation factors met-tRNA all bind mRNA sequence Sequence read 5' to 3' until AUG reached ATP to ADP energy used to recruit 60s subunit and remove GDP/ initiation factors/ capping proteins AUG is in ribosome in P site
Explain the process of elongation in translation
AUG and met-tRNA in p site, a site empty
aminoacyl tRNA binds at A site GTP –>Pi
Peptide bond forms chain in A site requires enzyme peptidyl transferase
gtp to gdp provides energy for translocation of chain to P site
A site now free for cycle above to repeat
What enzyme is required to form peptide bond in translation?
peptidyl transferase
How is translation terminated ?
Stop codon reached in A site
water enters ribosome and kicks out protein
