1. Translation is the process by which the information encoded in messenger RNA (mRNA) is used to synthesize proteins. The mRNA carries genetic information from DNA in the nucleus to the ribosomes in the cytoplasm. 2. Ribosomes contain two subunits that come together and use the genetic code carried by mRNA to link amino acids in the proper sequence to form a protein chain. 3. The three main steps of translation are initiation, elongation, and termination. Initiation involves binding of the small ribosomal subunit to the 5' end of mRNA along with initiator tRNA. Elongation adds amino acids one by one until a stop codon signals termination and the completed protein is released.

1. Microbial Genetics
Translation
Professor: Dr. Harvey, L. Laranang
D.M.D
Subj/Sec: DMb 121 / Dbb
Khafi Makoo, Noorallah

2. Translation mRNA---> Protein

4. GGeenneettiicc EExxpprreessssiioonn
• DNA Transcribed to RNA
• RNA Translated to Protein

5. TTrraannssllaattiioonn
• The process in which the information in the
nucleotide base sequence of mRNA is used to
dictate the amino acid sequence of a protein.
• 1 Strand RNA  Amino Acid Chain  Protein

6. RRNNAA aanndd PPrrootteeiinn SSyynntthheessiiss
• RNA is a Single Stranded Nucleic Acid
• RNA Acts as a Messenger between
DNA and Ribosomes
• Process Takes Amino Acids and Forms
Proteins

7. 5’-ATGCCTAGGTACCTATGA-3’
3’-TACGGATCCATGGATACT-5’
5’-AUGCCUAGGUACCUAUGA-3’
5’-AUG CCU AGG UAC CUA UGA-3’
N-MET-PRO-ARG-TYR-LEU-C
DNA
Transcription
decoded as
Translation
mRNA
Protein

8. TTrraannssllaattiioonn::
FFrroomm mmeesssseennggeerr RRNNAA ttoo pprrootteeiinn::
The information encoded in the DNA is transferred to
messenger RNA and then decoded by the ribosome to
produce proteins.

9. Protein synthesis ooccccuurrss oonn rriibboossoommeess

10. Protein synthesis ooccccuurrss oonn rriibboossoommeess

11. The large and ssmmaallll ssuubbuunniittss ccoommee ttooggeetthheerr
Mitochondrial
or Prokaryotic
ttoo ffoorrmm tthhee rriibboossoommee
Eukaryotic 60S subunit 80S ribosome 40S subunit

12. The association of the large and small subunits creates
the structural features on the ribosome that are essential
for protein synthesis
Three tRNA binding sites:
A site = amino-acyl tRNA
binding site
P site = peptidyl-tRNA
binding site
E site = exit site

13. In addition to the APE sites there is an mRNA binding
groove that holds onto the message being translated

14. There is a tunnel through the large subunit that allows
the growing polypeptide chain to pass out of the
ribosome

15. DNA
molecule
Gene 1
Gene 2
Gene 3
Review
DNA 5¢
DNA strand
(template)
3¢
TRANSCRIPTION
5¢ 3¢
Codon
mRNA
TRANSLATION
Protein
Amino acid
RNA
Protein

16. DNA
molecule
Gene 1
Gene 2
Gene 3
Review
DNA 5¢
DNA strand
(template)
3¢
TRANSCRIPTION
5¢ 3¢
Codon
mRNA
TRANSLATION
Protein
Amino acid
RNA
Protein

17. Second mRNA base
First mRNA base (5¢ end)
Third mRNA base (3¢ end)
Genetic
Code
64 codons
Codon Table

18. Amino acid
attachment site
tRNA structure
Hydrogen
bonds
3¢
5¢
Anticodon
Two-dimensional structure
Amino acid
attachment site
3¢
5¢
Hydrogen
bonds
Anticodon
3¢ 5¢
Anticodon
Three-dimensional structure Symbol used in this book

20. PPrrookkaarryyoottiicc RRiibboossoommeess ((7700 SS))

21. tRNA
molecules
Exit tunnel
Growing
polypeptide
Large
subunit
mRNA 3¢
Computer model of functioning ribosome
Small
subunit
5¢
E P A

22. Polypeptide
tRNA with
amino acid
attached
Ribosome
Anticodon
5¢ 3¢
mRNA
Amino
acids
Codons

23. Schematic model showing binding ssiitteess oonn rriibboossoommee
P site (Peptidyl-tRNA
binding site)
E site
(Exit site)
mRNA
binding site
A site (Aminoacyl-tRNA
binding site)
Large
subunit
Small
subunit
E P A

24. Amino end
mRNA
5¢
Growing polypeptide
Next amino acid
to be added to
polypeptide chain
tRNA
3¢
Codons
E
Schematic model with mRNA and tRNA
Ribosome translates 5’ to 3’ on mRNA.
Polypeptide chain grows amino end first, carboxyl end last.

25. Building a Polypeptide
• The three stages of translation:
– Initiation
– Elongation
– Termination
•All three stages require protein translation
factors

26. Ribosome Association and IInniittiiaattiioonn ooff TTrraannssllaattiioonn
1- Small ribosomal subunit binds
mRNA and special initiator tRNA (met-tRNAi)
(carries the amino acid methionine)
2- Small subunit scans along the mRNA until first start codon (AUG).
3- Initiation factors bring in large subunit
initiator tRNA occupies the P site.

27. Met
Initiator tRNA GTP
mRNA
5¢ 3¢
mRNA binding site
Small
ribosomal
subunit
Start codon
P site
E A
Large
ribosomal
subunit
5¢ 3¢
Translation initiation complex
GDP
Met

28. EElloonnggaattiioonn ooff tthhee PPoollyyppeeppttiiddee CChhaaiinn
- Amino acids are added one by one to the preceding
amino acid
-Elongation factors facilitate
- Codon recognition
- Peptide bond formation
- Translocation

29. TTeerrmmiinnaattiioonn ooff TTrraannssllaattiioonn
- Occurs when stop codon in mRNA reaches
A site of ribosome
- A site accepts protein called release factor
-Release factor causes addition of water molecule
instead of amino acid
- Polypeptide released, ribosomal subunits dissociate
and fall off mRNA

30. 3¢
Free
polypeptide
The release factor hydrolyzes the
bond between the tRNA in the
P site and the last amino acid of the
polypeptide chain. The polypeptide
is thus freed from the ribosome.
The two ribosomal subunits
and the other components
of the assembly dissociate.
Release
factor
Stop codon
(UAG, UAA, or UGA)
5¢
3¢
5¢
3¢
5¢
When a ribosome reaches a stop
codon on mRNA, the A site of the
ribosome accepts a protein called
a release factor instead of tRNA.

31. What Is the Function of Ribosomes?
Ribosomes are the sites in a cell in which protein synthesis takes place.
Cells have many ribosomes, and the exact number depends on how active
a particular cell is in synthesizing proteins. For example, rapidly growing
cells usually have a large number of ribosomes (Figure 1).

32. THANK YOU