Translation Flashcards
stop codons
3 (UAA, UAG, UGA)
signal to terminate transcription
do not code for amino acids
start codon
only one in eukaryotes
signal to start translation
codes for methionine (AUG)
large subunit of ribosome
contains tRNAs
made up on RNA and protein
small subunit of ribosome
binds to mRNA
made of protein and RNA
what synthesises rRNA
RNA polymerase 1
rRNA main concepts
not synthesised into protein
processed by cleavage and chemical modifications into its final form
packaged with proteins of the small and large subunits in the nucleolus then transported into the cytoplasm
what is a ribozyme
ribonucleic acid + enzyme
complex secondary structure
rRNA maturation in nucleolus
Precursor rRNA cleaved into 4
smaller products and processed
snoRNA
processes rRNA by guiding chemical modifications
non-protein coding
comes from introns
assembly of ribosome
in cytoplasm in presence of mRNA
what transcribes tRNA
RNA polymerase III
how does a specific amino acid link to the tRNA
covalent linkage
how is tRNA aminoacylated
aminoacyl-tRNA synthetase is an enzyme complex with binding sites for a specific amino acid, a specific tRNA and a molecule of ATP. pyrophopshate expelled from atp, amino acid covalently linked to 3’ of tRNA
translation pre initiation complex
small ribosomal subunit and tRNA with methionine
formation of pre initiation complex
cytoplasm: Met-tRNA binds small ribosomal
subunit then comes together with eIF2 and GTP
forms 40S complex
sedimentation coefficient
large number=travelled further=larger complex
mRNA binding to 40S complex
eIF4 proteins bind 5’ cap and more eIF proteins to form large complex. mRNA folded on itself through interaction between polyA tail binding
protein and eIF4 complex. eIF4 complex binds to eIF2 in the 40S subunit complex. 43S complex formed.
scanning for start site
mRNA unfolds once 43S complex formed. 40S complex moves along mRNA until it hits the first AUG codon (start site)
Met-tRNA anticodon binds AUG
ATP hydrolysis used
recruitment of large ribosomal subunit
GTP hydrolysis leads to release of eIF proteins and binding of Met-tRNA to large subunit
structure of large ribosomal subunit (binding sites)
3 binding sites: A site (aminoacyl-tRNA), P site (peptidyl-tRNA), E site (empty)
MET-tRNA in middle pocket
aminoacyl-tRNA binding
next aa-tRNA binds codon to A site
aa-tRNA is bound to EF1a + GTP
GTP hydrolysis
EF1 alpha
protein that helps bring charged tRNA into contact with assembled ribosome
result of GTP hydrolysis
conformational change in ribosome causing tRNA in A site to move, bringing the amino acid closer to tRNA in P site
transpeptidation
ribozyme catalyses the formation of peptide bond
Peptidyl transferase transfers the peptide onto the growing chain
Amino acid dissociates from tRNA
in the P site
tRNA now uncharged so can dissociate
tRNA in A position slides to P position
translocation
tRNA with polypeptide chain
(peptidyl-tRNA) moves into
the P site. ‘Empty’ tRNA moves to the E
site and is released. Powered by GTP hydrolysis
termination
Release factor protein complex binds a STOP codon
(eRF1 subunit)
No more peptide bonds can be formed as complex in A site
GTP hydrolysis (eRF3 subunit) à complex falls apart, releasing the new polypeptide
polyribosome
cluster of ribosomes translating the same mRNA molecule simultaneously so that multiple copies of protein are produced
free polyribosomes in cytosol
translate mRNA into proteins that function within the cytosol, cytoskeleton, mitochondria, peroxisomes, and the nucleus.
ER-bound poly ribosomes
translate mRNA into proteins that are processed in the ER and Golgi apparatus, and then directed to secretory vesicles, lysosomes, the cell membrane, or for secretion out of the cell.
which position in a codon has most variability
third
wobble base pairing
Base pairing is loose in the third position of tRNA-mRNA interaction]
Accounts for redundancy in last letter of codons in genetic code
Correlation between amino acid structure and 2nd position
Neutral or silent mutation – does not affect protein sequence- occurs in 2nd or 3rd positions
changes in this position often result in amino acids with similar properties
Ribonucleoprotein
RNA + protein complexes
eg ribosomes, eIF
RNA world hypothesis
RNA World: Early life forms relied solely on RNA for both genetic information and enzymatic functions.
RNA-Protein World: RNA molecules started interacting with proteins, with ribozymes (RNA-based enzymes) evolving into RNA-protein complexes.
Modern Molecular Biology: Today’s biology features distinct roles for DNA (genetic storage), RNA (intermediary and catalytic roles), and proteins (structural and functional).
dT is synthesised from dU
(suggests that U came first
