+ translation protein synthesis: ch 17 from : kevin brown – university of florida
TRANSCRIPT
+
Translation
Protein Synthesis: Ch 17From : Kevin Brown – University of Florida
+Protein Synthesis
Translation from mRNA
Codons to amino acids
http://www.youtube.com/watch?v=suN-sV0cT6c
+mRNA transcript organization
1) Open reading frame: codes for protein5’end has translational start site, 3’ end
has translational stop site
2) 5’ UTR – untranslated region (upstream of start site)
3) 3’ UTR – untranslated region (downstream of stop site)
+Typical mRNA molecule structure
+Codons
Codons are read from 5’ – 3’ in triplets
Genetic code
61 codons for amino acids, 20 amino acids
Amino acid sequence is determined by the complementary base pairing between mRNA codons and tRNA anticodons
+Translation – tRNA moleculetRNA – Transfer RNA – transfers amino
acids from cytoplasm to ribosome, where the amino acids get added onto a growing polypeptide chain.
Anticodon – triplet code found on tRNA, that is complementary to a specific mRNA codon.
Made of a single RNA strand that folds back on itself to form a 3 D structure – L-shaped.
+tRNA
64 codons
45 tRNA
Why?
Last base on tRNA anticodon is flexible – so some tRNA anticodons can recognize more than one codon
+Wobble
Non standard base pairing at 3’ end of codon – flexibilityMany tRNAs have inosine base at 5’ end of anticodon-Inosine can pair with A, U, or G
+tRNA bind to specific amino acid
Aminoacyl tRNA synthetase joins a particular amino acid to a tRNA through covalent bonding
There are 20 of these enzymes
Aminoacyl-tRNAsynthetase (enzyme)
Amino acid
P P P Adenosine
ATP
P
P
P
PPi
i
i
Adenosine
tRNA
AdenosineP
AMP
Aminoacyl tRNA(“charged tRNA”)
+Start signalsTranslational start signal
5’ AUG 3’ , which codes for Methionine
Which AUG is the start signal?Bacteria – often have Shine-Delgarno
sequence upstream from AUG
+
Eukaryotes – no Shine Delagarno, but a loose sequence – Kozak sequence
+rRNA - ribosomal RNA
Ribosome is made up of rRNA & proteins
Ribosome – the site of protein synthesis
Eukaryotes: Large subunit – 60 S, Small subunit – 40 S
Bacteria: Large subunit – 70S , Small subunit – 30 S
+Ribosome Schematic
Exit tunnel
A site (Aminoacyl-tRNA binding site)
Smallsubunit
Largesubunit
P A
P site (Peptidyl-tRNAbinding site)
mRNAbinding site
E site (Exit site)
E
+Protein Synthesis - Initiation
InitiatortRNA
mRNA
5
53Start codon
mRNA binding site
3
Translation initiation complex
5 33U
UA
A GC
P
P site
i
GTP GDP
Met Met
Largeribosomalsubunit
E A
5
Amino end
mRNAE
5 Codons
3
tRNA
Growing polypeptide
Next aminoacid to beadded topolypeptidechain
+Protein synthesis - ElongationAmino end ofpolypeptide
mRNA
5
E
Asite
3
E
GTP
GDP P i
P A
E
P A
GTP
GDP P i
P A
E
Ribosome ready fornext aminoacyl tRNA
Psite
1) Codon recognition
2) Peptide bond formation
3) Translocation
+
Releasefactor
Stop codon(UAG, UAA, or UGA)
3
5
3
5
Freepolypeptide
2 GTP
5
3
2 GDP 2 iP
Protein synthesis - Termination
+Translation animation
http://www.youtube.com/watch?v=Ikq9AcBcohA
+Energy usage during Translation tRNA Charging – ATP to AMP + PPi for each
amino acid covalently bonded to tRNA
Initiation – 1 ATP to ADP + Pi and 1 GTP to GDP + Pi hydrolyzed during formation of initiation complex
Elongation – 2 GTP hydrolyzed per amino acid 1 for codon recognition 1 for energy for translocation of tRNA from A to
P
Termination – 1 GTP to GDP + Pi hydrolyzed in termination
+Completing the protein
Folding (may be helped w/chaperone protein)
Post-translational modifications:Chemical modifications – add groupsRemove amino acids from leading end
of polypeptide chainCleavage of protein
+Some polypeptides get targeted to specific locationsAll ribosomes start free
If polypeptide gives signal, ribosome binds to ER.
Signal peptide is at leading (NH3) end of polypeptide
Signal recognition particle (SRP) – recognized signal peptide and brings into receptor protein in ER
Protein either is in ER lumen, or may end up as part of membrane
+MutationsChanges in genetic information of cell
(or virus)
Small scale – few nucleotides:Substitution, insertion, deletionFrameshift are most damaging
Large scale – chromosomal changes
+Translation
http://www.dnalc.org/view/15501-Translation-RNA-to-protein-3D-animation-with-basic-narration.html