Translation Flashcards
only …. is translated?
mRNA
what do all polypeptides begin with?
methionine - because all mRNA molecules begin with the codon ‘AUG’
what three steps does translation involve?
initiation
elongation
termination
what does initiation consist of?
assembly of the three components that carry out the process
(ribosome, tRNA, mRNA)
What does elongation involve?
stepwise addition of amino acids to the growing protein chain
what does termination involve?
stop codon is encountered, triggering dissociation of complex
structure of ribosome?
made up of: protein, rRNA, active site that catalyses addition of amino acid to polypeptide chain
what does the large subunit of the ribosome include?
50S - contains three slots for tRNAs
what does the small ribosomal subunit involve?
30S - contains the mRNA binding site
what are the three slots found in the large subunit of the ribosome?
APE
A - aminoacyl - tRNA
P - peptidyl-tRNA
E - exit
which mutations causes a severe loss of function resulting from a change in the reading frame?
insertion or deletions of 1,2,4,5 etc. nucleotides
which mutations would have little effect on the phenotype and why?
insertion or deletions of 3,6,9 etc. because the reading frame is not affected for the most of the mRNA
what enzyme is used to load tRNA with the correct amino acid?
enzymes called aminoacyl-tRNA synthetases –> they are specific for each amino acid
Describe the 1st stage of initiation:
complex of small ribosomal subunit and initiator tRNA (UAC anticodon) binds to 5’ cap
Describe the 2nd stage of initiation:
complex moves along mRNA in 3’ direction scanning for AUG start codon
Describe the 3rd stage of initiation:
tRNA molecule binds to the codon via its anticodon
Describe the 4th stage of initiation:
Large ribosomal subunit aligns itself to the tRNA molecule at the ‘P’ site and forms a complex with the small subunit
Describe the 1st stage of elongation:
second tRNA molecule pairs with the next codon in the ribosomal A site
Describe the 2nd stage of elongation:
the amino acid in the P site is covalently attached via a peptide bond (condensation reaction) to the amino acid in the A site
Describe the 3rd stage of elongation:
tRNA in the P site is now de-acylated (no amino acid), while the tRNA in the A site carries the peptide chain
Describe the 4th stage of elongation:
the ribosome moves along the mRNA strand by one codon position (in a 5’-3’ direction)
Describe the 5th stage of elongation:
De-acylated tRNA moves into the E site and is released, while the tRNA carrying the peptide chain moves to the P site (translocation)
Describe the 6th stage of elongation:
new tRNA attaches to the next codoin in A site
Describe the 1st stage of termination:
elongation and translocation continue until the ribosome reaches a stop codon
Describe the 2nd stage of termination:
stop codons do not recruit a tRNA molecule, but instead recruit a release factor that signals for translation to stop
what are the three stop codons?
UAA
UAG
UGA
What is the 3rd stage of termination?
polypeptide is released and the ribosome dissociates into its two independent subunits
Describe the 4th stage of termination:
the polypeptide is ready for post-translational modification, folding and sorting
