Translation Flashcards
Commaless
codons aren’t separated by noncoding bases.
They are read continually without punctuation, no indication of one codon stopping and another starting
Reading Frame
The reading frame starts with a start codon and ends with a stop codon.
Modified bases in tRNA
Adenine to inosine (I)
Uridine to pseudouridine (w)
Uridine to dihydro-uridine (D)
Use of modified bases
The different base pairs give the tRNA a shape that fits better in the ribosome.
tRNA ends
…CCA-3’
amino acid binding site
5’-G…
forms acceptor stem with binding site
aminoacyl tRNA synthetase
enzyme that charges tRNA
specificity for amino acid, so 20 of them; services multiple tRNA types
aminoacyl tRNA synthetase reactions
Amino acid links with ATP; carboxyl group links to AMP phosphate, forming aminoacyl AMP
Amino acid attaches to tRNA; aminoacyl AMP’s carboxyl end is transferred to A at binding site
Isoaccepting
Prok. ribosomes & components
70s
50s large
peptidyl transferase / 23s rRNA
30s small
16s rRNA
necessary components for protein synthesis initiation
mRNA
50s & 30s
initiation factors (IFs)
tRNAfMet, special initiator tRNA
Guanosine triphosphate (GTP)
IF1
In translation initiation, IF1 blocks the A site from being bound by the tRNA
IF2
In translation initiation, IF2 is a GTPase that forms a complex with GTP. This recruits a charged tRNA, which it binds to the P site.
IF3
In translation initiation, IF3 prevents the 30s from binding prematurely to the 50s
Shine-Dalgarno
exists upstream of the start codon in the mRNA.
It is a conserved ribosome binding sequence (RBS).
base pairing with the 16s rRNA in the 30s enables proper positioning of the mRNA
aligns the AUG start codon
30s initiation complex
initiator tRNA binds to mRNA through complementary base pairing
Prok. docking
GTP is hydrolyzed by IF2. This provides energy for the release of the IFs, and the positioning of tRNAfMet at the P site.
IF3 is released and the 70s is formed.
necessary components for protein synthesis elongation
The 70s complex
Charged tRNAs
Elongation factors (EFs; EF-Tu and EF-G)
GTP
EF-Tu
binds and transports aminoacyl-tRNA to the ribosome during elongation.
GTP hydrolysis allows the tRNA to enter the A site,
When the anticodon binds the codon, EF-Tu dissociates.
Peptidyl transferase
Ribozyme in the 50s
transfers chain at P site onto tRNA’s aa at P site
breaks bond at P, catalyzes formation of peptide bonds at A
EF-G
helps move tRNA and mRNA through the ribosome
GTP-form EF-G binds near A site on 50s
GTP hydrolyzed
phosphate release induces movement of A to P and P to E
RFs
recognize the stop codon so termination can begin
facilitate termination by releasing the polypeptide and disassembling the translational complex
stop codons
UAG, UAA, UGA
RF1
UAA, UAG
RF2
UAA, UGA
RF action
RF at A breaks bond linking the polypeptide to P
RF3 forms complex with GTP, binds ribosome
RF3 complex releases everything from the ribosome and dissociates subunits
eIFs
eukaryotic initiation factors which form the initiation complex
eIF4E
eIF4G
eIF4E
cap-binding protein; binds to 5’ cap
eIF4G
scaffold protein; interacts with both PABPs and eIF4E
cap-binding complex
The cap-binding complex (eIFs, tRNAMet, 40s) explores for the start codon.
Identifies proper start by the Kozak sequence
closed loop structure
5’ cap and 3’ tail connect
The cap binding protein (eIF4E) binds to the 5’ m7G cap.
The poly-A binding proteins attach to the 3’ poly-A tail.
The scaffold protein eIF4G interacts with e1F4E & the binding proteins.
This links the 2 ends.
Kozak sequence
The Kozak sequence is a consensus sequence surrounding the start codon.
The identification of the start codon depends on the Kozak sequence.
ribosome binding site on the mRNA
Misfolded proteins are generally recognized and degraded. How
tagged for degradation by ubiquitin
ubiquitin-tagged protein enters a proteasome
proteasome and ubiquitin are recycled, protein broken down in proteasome
PRIMARY folding organization level
The sequence of amino acids; a regular polypeptide.
This determines the characteristics of higher levels or organization.
SECONDARY folding organization level
SECONDARY
Parts of the polypeptide form repeating configurations, maintained by H-bonds.
alpha helix, beta pleated sheet
TERTIARY organization
TERTIARY
3D conformation of the entire chain in space.
Results from further arrangement of secondary structures, due to interactions between R groups.
QUATERNARY organization
QUATERNARY
Applies to proteins composed of multiple polypeptides.
Indicates position of the chains in relation to each other.
iSOACCEPTING
tRNA same aa, different anticodon
