Translation is the process by which a messenger RNA is used to direct the synthesis of a polypeptide chain. It involves three main stages: initiation, elongation, and termination. During initiation, the small ribosomal subunit binds to the mRNA start codon along with initiator tRNA. In elongation, amino acids are sequentially added to the growing polypeptide chain according to the mRNA codons. Termination occurs when a stop codon is reached, releasing the complete polypeptide chain. The process requires specific transfer RNAs that match codons and carry corresponding amino acids.

1. Translation is the RNA-Directed
Synthesis of a Polypeptide
William Chen
Maggie McCormick
Esther Park

2. Molecular Components of Translation
• tRNA (transfer RNA) the function is to literally
transfer amino acids.
• The one end of the tRNA is a anticodon (a
nucleotide triplet). TRANSCRIPTION DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Amino
Polypeptide acids
tRNA with
amino acid
Ribosome attached
Gly
tRNA
A A A
Anticodon
U G G U U U G G C
5 Codons 3
mRNA

3. tRNA is Form = Function
• Transfer RNA (tRNA) molecules are transcribed
from DNA templates.

4. • Two dimensional structure.Amino acid 3
A
C
attachment site
A 5
C G
G C
C G
U G
U A
U A U
UC U
* C A C AG A AG *
G * CUC *
C G U GU * CGAG G
** UC * AGG
*GAGA C
G C Hydrogen
U A bonds
* G
A * AC
*
A
U
AG
Figure 17.14a Anticodon

5. • Three dimensional structure
Amino acid
5
3attachment site
Hydrogen
bonds
AAG
3 5
Anticodon
Anticodon
(c) Symbol used
(b) Three-dimensional structure in this book

6. Accurate Translation
• There must be a correct match between a tRNA
and an amino acid.
• Then there is an involvement of a correct match
between the tRNA anticodon and a mRNA
codon.
• The base pairing for tRNAs are not as strict as
DNA or mRNA codons. This is called “wobble”
where the third base pairing is more flexible
than any other bases.

7. Ribosomes
• Facilitate the specific coupling of tRNA
anticodons with mRNA codons during protein
synthesis.
• There are tRNA, mRNA, and rRNA.

8. Translation : Building a Polypeptide
• Translation has 3 stages:
▫ Initiation
▫ Elongation
 Codon Recognition
 Peptide bond formation
 Translocation
▫ Termination

9. Initiation (requires GTP)
• During Initiation, Initiation factors bring
mRNA, tRNA, and two ribosomes together.
• First, a ribosome binds to mRNA to a initiator
tRNA.
• Then, the initiator tRNA hydrogen bonds with
the start codon(AUG).
• After this, a large ribosomal subunit is attached
and completes initiation.

10. Initiation(Pg.323)

11. Elongation
• Amino acids are added one by one. For every
addition, a protein called elognation factors are
involved.
• Codon Recognition(requires GTP)
• Peptide bond formation
• Translocation (requires GTP)

12. Elongation (Page 324)
E site
A site
P site

13. Termination
• Elongation stops when the ribosome reaches a
stop codon in the mRNA.
• UAG, UAA, and UGA are the triplets for stop
codons.
• A protein called a release factor goes on the A
site instead of a tRNA.
• The factor hydrolyzes the polypeptide from the
tRNA and makes the polypeptide go to the exit
tunnel.
• The tunnel then breaks down.

14. Termination(Pg.325)

15. Polyribosomes
• Once a ribosome moves past the start codon, a
second ribosome may attach more than one
ribosome. These are found in both eukaryotes
and prokaryotes.

16. Completing and targeting the
functional protien
• Translation isnt sufficent enough to make a
functional protien
• What it uses is…
▫ Protien folding
▫ Post-translational modifications

17. Protein Folding
• Polypeptide chains coil and fold to make a
tertiary structure

18. Post-translational modifications
• Certain amino acids may be chemically modified
by the attatchment of sugars, lipids phosphate
groups and others

19. Targeting polypeptides to specific
locations
• Protien synthesis happens in both
▫ Free ribosomes (synthesize proteins that dissolve
in the cytosol and function there)
▫ Bound ribosomes (synthesize proteins of the
endomembrane system as well as proteins
secreted from the cell)

20. Vocabulary
• Signal peptide – targets the protein to the ER
(see figure 17.21)
• Signal-recognition particle (SRP) – a protein-
RNA complex that recognizes a signal peptide as
it emerges from the ribosome.

21. tRNA YOUTUBE IT!!!!
• http://www.youtube.com/watch?v=gE46bMA0
Z14
• http://www.youtube.com/watch?v=Deie92DylR
M