This document summarizes translation mechanisms in prokaryotic and eukaryotic systems. It discusses that translation is the process of protein synthesis from mRNA, involving ribosomes, tRNAs, and enzymes. The three main steps of translation - initiation, elongation, and termination - are described for both prokaryotic and eukaryotic systems. Key differences between the two systems are the use of Shine-Dalgarno sequences and initiation factors in prokaryotes versus Kozak sequences and more complex initiation factor involvement in eukaryotes. Termination and ribosome recycling mechanisms are also compared between prokaryotes and eukaryotes.

1. ‘Translational mechanisms in
Prokaryotic and Eukaryotic
systems’
Presented by:
Masoom Raza
PhD 1st year(Life Sciences)
Shiv Nadar University 1

2. What is translation?
Translation is the process of protein synthesized from the information contained in a molecule of mRNA
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4. Component of translation
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5. Ribosomes: Role In Translation
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Enzymes
 Aminoacyl tRNA Synthetase: catalyze the attachment of tRNA molecule to its respective amino acid.
- At least one for each tRNA.
- Attachment of amino acid activates/charges the tRNA molecule.
 Peptidyl Transferase: catalyzes the sequential transfer of amino acid to the growing chain.
- Forms the peptide bond between the amino acids.

7. tRNAs : tRNA acts as an adaptor between
the codons and the amino acids they specify.
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9. Mechanism Of Translation
 Three steps of translation:
- Initiation: Sets the stage for polypeptide synthesis
- Elongation: Causes the sequential addition of amino acids to
the polypeptide chain as determined by mRNA
- Termination: Brings the polypeptide synthesis to the halt
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Translation in Prokaryotic system

11. Shine-Dalgarno Sequences
 The Shine-Dalgarno sequence was proposed by Australian scientists John Shine and Lynn Dalgarno.
 The Shine-Dalgarno (SD) sequence is a ribosomal binding site in bacterial and archaeal messenger RNA,
generally located around 8 bases upstream of the start codon AUG
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12. Initiation
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13. Translocation
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14. Elongation
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15. Termination
One of the stop or termination signals (UAA, UAG
and UGA) terminates the growing polypeptide.
• When the ribosome encounters a stop codon,
- there is no tRNA available to bind to the A site of the
ribosome,
- instead a release factor binds to it.
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Translation in Eukaryotic System

17. Kozak sequence
 The Kozak consensus sequence, Kozak consensus or Kozak sequence is a
sequence which occurs on eukaryotic mRNA and has the consensus
(gcc)gccRccAUGG.
 Kozak consensus sequence plays a major role in the initiation of the translation
process. The sequence was named after the person who brought it to prominence,
Marilyn Kozak.
 This sequence on an mRNA molecule is recognized by the ribosome as the
translational start site, from which a protein is coded by that mRNA molecule.
The ribosome requires this sequence, or a possible variation (see below) to
initiate translation.
 The Kozak sequence is not to be confused with the ribosomal binding site (RBS),
that being either the 5' cap of a messenger RNA or an Internal ribosome entry site
(IRES)
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18. Scanning model of Initiation
Proposed by M. Kozak
 Small subunit of ribosome (initiation factor, GTP, tRNAiMet) binds to the 5’ cap and scan
along with mRNA until the 1st AUG.
 Translation starts at the 1st AUG
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19. The initiation of translation in eukaryotes is complex,
involving at least 10 eIFs & divided into 4 steps :
a. Ribosomal dissociation.
• The 80S ribosome dissociates to form 40S & 60S subunits.
• Two initiating factors namely elF-3 & elF-1A bind to the newly formed 40S
subunit &thereby block its reassociation with 60S subunit.
b. Formation of 43S pre-initiation complex.
• A ternary complex containing met-tRNA′ & elF-2 bound to GTP attaches to
40S ribosomal subunit to form 43S preinitiation complex.
• The presence of elF-3 & elF-1A stabilizes this complex.
c. Formation of 48S initiation complex.
• The binding of mRNA to 43S preinitiation complex results in the formation
of 48S initiation complex through the intermediate 43S initiation complex.
• elF-4F complex is formed by the association of elF-4G, elF-4A with elF-
4E.The elF-4F (referred to as cap binding protein) binds to the cap of mRNA.
d. Formation of 80S initiation complex.
• 48S initiation complex binds to 60S ribosomal subunit to form 80S initiation
complex.
• The binding involves the hydrolysis of GTP (bound to elF-2). This step is
facilitated by the involvement of elF-5.
• As the 80S complex is formed, the initiation factors bound to 48S initiation
complex are released & recycled.
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20. Elongation
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21. Termination
• In eukaryotes, a single release factor- eukaryotic
release factor 1 (eRF1)-recognizes all three stop
codons, and eRF3 stimulates the termination events.
• once the release factor binds, the ribosome unit falls apart,
- releasing the large and small subunits,
- the tRNA carrying the polypeptide is also released,
freeing up the polypeptide product.
• Ribosome recycling occurs in eukaryotes.
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22. Ribosome Recycling
 After the release of polypeptide and the release factors the ribosome is still
bound to the mRNA and is left with two deacylated tRNA (in the P and E sites)
 To participate in a new round of polypeptide synthesis, these mRNA and the
tRNA must be released and the ribosome must dissociate into small subunit
and large subunit
 Collectively these events are termed as ribosome recycling
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24. Thank You
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