1. Translation
Apr 25, 2018

4. 1968 Nobel Prize

7. Components of Translation
1. mRNA
2. tRNAs
3. Aminoacyl-tRNA synthetases
4. Ribosome
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis

8. mRNA Structure Bacterial mRNA and Eukaryotic mRNA
Look at these pictures and compare and contrast bacterial and eukaryotic mRNA.
a) Bacterial mRNA
5’ UTR
ORF
3’ UTR
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis
b) Eukaryotic mRNA
5’ UTR
ORF
3’ UTR

9. mRNA Structure Bacterial mRNA and Eukaryotic mRNA
Both have 5’ and 3’ UTRs (UnTranslated Region)
Both have the start codon AUG
Both have the stop codons UAG, UAA and UGA
Both have coding sequences or ORFs (Open Reading Frames)
a) Bacterial mRNA
5’ UTR
ORF
3’ UTR
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis
b) Eukaryotic mRNA
5’ UTR
ORF
3’ UTR

10. mRNA Structure Bacterial mRNA only
Ribosome-binding sites; also called Shine-Dalgarno sequence
Eukaryotic mRNA only
5’ Cap (methylated guanine)
Poly A tail
Kozak Sequence (sometimes present); enhances ribosome binding
a) Bacterial mRNA
5’ UTR
ORF
3’ UTR
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis
b) Eukaryotic mRNA
5’ UTR
ORF
3’ UTR

16. Aminoacyl-tRNAs Synthetase
Each of the 20 amino acids are attached to the appropriate tRNA by a dedicated aminoacyl-tRNA synthetase. So there are usually 20 aminoacyl-tRNA synthetase.
“Charging” : couples a particular amino acid to its corresponding tRNA.
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis
How is ATP used?

23. Ribosomes
The ribosome catalyzes a single reaction: The formation of a peptide bond.
High Energy Bond Broken

24. RNA component of the Ribosome
The RNA component in the ribosome acts as a ribozyme!
It catalyzes the peptidyl transferase reaction which forms peptide bonds between two adjacent amino acids
Prokaryotes
The 23S RNA component in the 50S ribosome subunit
Eukaryotes
The 28S RNA component in the 60S ribosome subunit.

25. Peptidyl Transferase Reaction
Peptidyl-tRNA = a tRNA molecule that is attached to an amino acid at its 3’ end. This amino acid is also part of the growing polypeptide chain
Aminoacyl-tRNA = a tRNA molecule that is attached to an amino acid at its 3’ end. The amino acid is not yet incorporated into the polypeptide chain.

26. tRNA binding sites E= Exit site
P= Binding site for the Peptidyl-tRNA (charged tRNA in which amino acid is attached to the growing polypeptide chain)
A = Binding site for Aminoacylated-tRNA (charged tRNA in which the amino is NOT attached to the growing polypeptide chain).

34. Prokaryotic Initiation
The start codon is typically AUG
Therefore, the initiator tRNA anticodon is CAU
Corresponding amino acid is methionine
The initiator tRNA molecules is like no other
The methionine has a special modification converting it to N-formyl methionine (fMet)

35. Prokaryotic Initiation
Initiation factors bind to the 30S ribosome
Recruits initiator tRNA (fMet)
Ribosome with tRNA (fMet) binds to the ribosome binding site
Large ribosomal subunit 50S binds to create the whole complex forming the 70S initiation complex

36. Eukaryotic Initiation
Kozak sequence just upstream of the start codon. Increases the efficiency.
5’ Cap recruits the ribosome, the ribsome then scans the mRNA until it reaches a start codon
5’ UTR
ORF
3’ UTR
In rapidly growing bacterial cells, 80% of the cells energy is used for translation
50% of the cells dry weight is proteins used for protein synthesis

39. Translation Termination
There are no tRNAs that recognize stop codons.
A occupied “P” site but an unoccupied “A” is a signal to a protein called the release factor to binding the the A site and dissociate the ribosome assembly.
In the standard genetic code, there are three mRNA stop codons: UAG ("amber"), UAA ("ochre"), and UGA ("opal" or "umber").