Translation Flashcards
Eukaryotic ribosomes are a complex of
rRNA and 82 ribonucleoproteins
40S + 60S assemble into the 80S ribosome for translation
Steps of translation (3)
- initation
- elongation
- termination
Translation begins with the codon
AUG
Which codes for methionine carried by a special tRNA called an initiator tRNA
The initiator tRNA carries
Methionine and binds to the P site of the small subunit before the ribosome is fully assembled
Eukaryotic initiation factors (eIFs) functions (2)
- help load the initiator tRNA into the small subunit of the ribosome
- help bind the 5’ end of mRNA into the ribosome
eIF4E binds
to the 5’ GTP cap
EPA are the
tRNA binding sites in the ribosome
Translation terminates with the codon
UAA/UAG/UGA
release factors bind to the A site containing the stop codon forcing peptidyl transferase to hydrolyse water instead of an a.a.
Post translational modifications (6)
- phosphorylation (via kinases: cell cycle and signal transduction)
- methylation (via methyl transferases: inc+ hydrophibicity and epigenetics)
- glycosylation (affect protein folding and conformation)
- proteolysis (activating proteins)
- n-acetylation (transfer acetyl group to N terminus to replace Met, gene expression regulation)
- lipidation (inc+ hydrophibicity, destined for membranes)
mRNA turnover is the
rate at which mRNA is degraded
mRNA is degraded by nucleases, the exosome and decapping proteins
Steps of mRNA degradation (2)
- RNA deadenylase + exonucleases degrade the poly A tail
- Decapping proteins + Xrn1p remove the 5’ GTP cap
mRNA degradation is determined by
RBPs
RNA binding proteins
bind specific sequences within mRNA that regulate stability
What binds to RBPs to increase degradation
AREs
AU rich elements
What binds to RBPs to decrease degradation
CREs
stabilise mRNA
Nonsense mediated decay is
an mRNA surveillance system that selectively degrades transcripts containing PTCs
PTC= premature termination codon
PTCs can form via (3)
- point mutations
- frame shifts
- splicing errors
PTCs are recognised during
translation
exon exon junction complexes are protein complexes that have been formed through splicing
these are removed after translation
if any remain, NMD is activated
Exon exon junctions are
proteins that form a complex marking the site of a successful splicing event
if any remain on the mRNA after translation, NMD is activated
miRNAs
micro RNAs
small non-coding RNA molecules (about 22 nucleotides)
function in RNA silencing and post-transcriptional regulation of gene expression via base-pairing with complementary sequences within mRNA molecules
lncRNAs
long non coding RNAs
also regulate mRNA stability
Genes can be regulated by (6)
- changes in chromatin
- transcriptional changes
- changes in mRNA processing
- altered translation
- altered mRNA turnover
- ncRNAs
