1. Protein Synthesis: Ch 17 From : Kevin Brown – University of Florida
Translation
Protein Synthesis: Ch 17
From : Kevin Brown – University of Florida

2. Protein Synthesis Translation from mRNA Codons to amino acids
-sV0cT6c

3. mRNA transcript organization
1) Open reading frame: codes for protein
5’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)

4. Typical mRNA molecule structure

5. 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

6. Translation – tRNA molecule
tRNA – 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.

7. tRNA
64 codons
45 tRNA
Why?
Last base on tRNA anticodon is flexible – so some tRNA anticodons can recognize more than one codon

8. Wobble Non standard base pairing at 3’ end of codon – flexibility
Many tRNAs have inosine base at 5’ end of anticodon-
Inosine can pair with A, U, or G

9. tRNA bind to specific amino acid
Aminoacyl-tRNA synthetase (enzyme)
Amino acid P
Adenosine
ATP i
tRNA
AMP
Aminoacyl tRNA (“charged tRNA”)
Aminoacyl tRNA synthetase joins a particular amino acid to a tRNA through covalent bonding
There are 20 of these enzymes

10. Start signals Translational start signal
5’ AUG 3’ , which codes for Methionine
Which AUG is the start signal?
Bacteria – often have Shine-Delgarno sequence upstream from AUG

11. Eukaryotes – no Shine Delagarno, but a loose sequence – Kozak sequence

12. 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

13. Ribosome Schematic Exit tunnel A site (Aminoacyl- tRNA binding site)
Small subunit
Large subunit P A
P site (Peptidyl-tRNA binding site)
mRNA binding site
E site (Exit site) E

14. Protein Synthesis - Initiation
Initiator tRNA
mRNA 5 3
Start codon
mRNA binding site
Translation initiation complex U A G C P
P site i 
GTP
GDP
Met
Large ribosomal subunit E

15. Amino end
mRNA E 5
Codons 3
tRNA
Growing polypeptide
Next amino acid to be added to polypeptide chain

16. Protein synthesis - Elongation
Amino end of polypeptide
mRNA 5 E
A site 3
GTP
GDP  P i A
Ribosome ready for next aminoacyl tRNA
P site
1) Codon recognition
3) Translocation
2) Peptide bond formation

17. Protein synthesis - Termination
Release factor
Stop codon
(UAG, UAA, or UGA) 3 5
Free polypeptide 2
GTP
GDP  i P

18. Translation animation
BcohA

19. 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

20. Completing the protein
Folding (may be helped w/chaperone protein)
Post-translational modifications:
Chemical modifications – add groups
Remove amino acids from leading end of polypeptide chain
Cleavage of protein

21. Some polypeptides get targeted to specific locations
All 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

23. Mutations Changes in genetic information of cell (or virus)
Small scale – few nucleotides:
Substitution, insertion, deletion
Frameshift are most damaging
Large scale – chromosomal changes

24. Translation
Translation-RNA-to-protein-3D-animation- with-basic-narration.html