2. Table of contents
01 03
02 04
Definition Tools Differences in
Eukaryote &
Prokaryote
Initiation
05 06 07
Elongation Termination Post Translation
Modification
3. Definition
● Translation is basically a synonym
process of protein synthesis.
● It is the process in which the protein is
synthesized from the information
contained in a molecule of messenger
RNA (mRNA).
● It can defined as “ the process by which
the sequence of nucleotides in a
messenger RNA molecule directs the
incorporation of amino acid into protein.”
4. Translation Process
In a prokaryotic cell, transcription and translation are coupled;
that is, translation begins while the mRNA is still being
synthesized. In a eukaryotic cell, transcription occurs in the
nucleus, and translation occurs in the cytoplasm.
Translation involves three major steps :
1. INITIATION
2. ELONGATION
3. TERMINATION
5. Tools/Machinery
The machinery required for translating the language of messenger RNAs
into the language of proteins is composed of
mRNAs : Messenger RNA (mRNA) provides an intermediate that carries
the copy of a DNA sequence that represents protein
tRNAs : tRNA acts as an adaptor between the codons and the amino
acids they specify.
Enzymes : Required for the attachment of amino acids to the correct
tRNA molecule. (Aminoacyl-tRNA Synthetase, Peptidyl Transferase.
Ribosome : It is the macromolecular complex that directs the synthesis
of proteins.
Translational Factors : to help translation happens
6.
7. Ribosome Structure
● Small & large ribosomal subunits.
● A Binding site for the mRNA is present on
small subunit.
● Two binding sites
(P & A) bind tRNAs on large subunit.
1. P site – holds the tRNA carrying the
growing polypeptide chain.
2. A site – holds the tRNA with the next AA to
be added.
● Ribosomes hold the mRNA and tRNAs
together and connect the amino acids at the A
site to the growing polypeptide.
8. Structure of tRNA
● Aligns each amino acid with the
corresponding codon
● 70-80 nt long
● 3’ end has the 5’- CCA sequence to which
aa are linked
● The opposite end contains the anticodon
loop
● Contains modified bases
9. Prokaryotic And Eukaryotic Translation
mRNA structure: In prokaryotes, mRNA is usually
polycistronic, meaning that it contains multiple coding
regions (known as cistrons) that can be translated into
multiple proteins. In contrast, eukaryotic mRNA is
typically monocistronic, meaning it carries the
information for only one protein.
Transcription and translation coupling: In prokaryotes,
transcription and translation occur simultaneously in the
cytoplasm, as there is no nuclear membrane to separate
these processes. This allows for rapid protein synthesis. In
eukaryotes, transcription occurs in the nucleus, and the
mRNA is then transported to the cytoplasm for translation.
The separation of transcription and translation in
eukaryotes allows for additional processing steps, such as
RNA splicing and modification, before translation can
occur.
10. Ribosomes: Prokaryotes have smaller ribosomes compared to eukaryotes. Prokaryotic ribosomes consist of a 30S small
subunit and a 50S large subunit, while eukaryotic ribosomes consist of a 40S small subunit and a 60S large subunit.
These differences in ribosome structure contribute to variations in translation initiation and elongation between the
two groups.
Initiation of translation: In prokaryotes, translation initiation is facilitated by the Shine-Dalgarno sequence, which is
located upstream of the start codon on the mRNA. This sequence base pairs with the ribosomal RNA (rRNA) of the small
ribosomal subunit, allowing for the correct positioning of the ribosome on the mRNA. Eukaryotic translation initiation
involves a more complex process, where the small ribosomal subunit binds to the 5' cap structure of the mRNA and
scans along the mRNA until it recognizes the start codon.
The termination of translation: In prokaryotes involves the recognition of stop codons (UAA, UAG, or UGA) by release
factors, leading to the release of the completed polypeptide chain. In eukaryotes, termination occurs when the
ribosome encounters a stop codon, and release factors facilitate the release of the polypeptide chain. Additionally,
eukaryotes often undergo a polyadenylation process at the 3' end of the mRNA, which aids in termination and
subsequent mRNA degradation.
Post-transcriptional modifications: Eukaryotic mRNA undergoes several modifications before translation. These
modifications include the addition of a 5' cap and a poly(A) tail, as well as RNA splicing to remove non-coding regions
called introns. In prokaryotes, mRNA lacks these modifications and is generally ready for translation immediately after
transcription.
11. Processing of eukaryotic M-RNA
RNA processing achieves three things:
1) Removal of Introns
2) Addition of a 5’ cap
3) Addition of a 3’ tail
lThe mRNA then moves out of the nucleus
and is translated in the cytoplasm.
12. Initiation
● Rate limiting step
● Requires hydrolysis of ATP and GTP
● Results in formation of a complex containing the mRNA, the
ribosome and the initiator Met-tRNA
A. 5’ end (Cap) dependent initiation:
The initiation complex binds to the 5’ cap structure and scans in a
5’ to 3’ direction until initiating AUG is encountered
A. Cap independent initiation/ Internal ribosome entry:
Initiation complex binds upstream of initiation codon
14. 5’ end (cap) dependent initiation:
● The first step is the recognition of the 5’ cap by eIF4F, which
consists of three proteins, eIF4E, eIF4G and eIF4A.
● Cap binding protein, eIF4E, binds to cap
● The N-terminus of eIF4G binds eIF4E and the C-terminus
binds eIF4A
● The 40S subunit binds to eIF4G via eIF3
15. Cap-Dependent Initiation of Protein Synthesis in
Eukaryotes
● An initiation complex forms at the cap with the 40S ribosomal
subunit and other translation initiation factors.
● The 40S complex then scans down the 5’ untranslated region to
the first AUG codon. The scanning process is aided by eIF4F and
other initiation factors.
● When the start codon is recognized, the initiator tRNA (carrying
methionine or formylmethionine) bound to eIF2-GTP (eukaryotic
initiation factor 2 with GTP) is positioned at the P site of the
ribosome.
● A GTP hydrolysis step by eIF5 triggers GDP binding of eIF2 and
release of initiation proteins.
● The large ribosomal subunit (60S) associates with the small
subunit, forming a complete ribosome, the 80S ribosome
initiates translate the ORF. Several eukaryotic initiation factors,
including eIF5B and eIF6, are involved in this process.
● GTP hydrolysis occurs when the ribosome correctly recognizes
the start codon. This hydrolysis releases initiation factors from
the ribosome
17. Elongation
- Ribosome selects
aminoacylated tRNA
- eEF1 and GTP are bound to
aminoacylated tRNA
- Ribosome catalyzes formation
of a peptide bond
- Translocation is dependent on
eEF2 and GTP hydrolysis
- Many ribosomes may translate
mRNAs simultaneously on the
same strand.
18. Elongation process
- The 80S initiation complex contains met tRNA′ in the A-site is free.
- Another Aminoacyl-tRNA is placed in the A-site.
- This requires proper codon recognition on the mRNA & involvement of
elongation factor 1a (EF-1a) & supply of energy by GTP.
- The Aminoacyl-tRNA is placed in the A-site, EF-1a & GDP are recycled to bring
another Aminoacyl-tRNA.
- The enzyme Peptidyl transferase catalyzes the formation of peptide bond.
- Net result of peptide bond formation is the attachment of the growing
peptide chain to the tRNA in the A-site.
- The ribosome moves to the next codon of the mRNA (towards 3'-end).
- This process called translocation, involves the movement of growing peptide
chain from A-site to P-site.
- Translocation requires EF-2 & GTP.
- GTP gets hydrolyzed and supplies energy to move mRNA.
- EF-2 & GTP complex recycles for translocation.
19. Terminatio
n
- Entry of stop codons
UAG, UGA, or UAA the A site of the
ribosome
- Release-factor recruitment(eRF1)
Release factors are recruited when
a stop codon occurs at the A site
- Polypeptide release
eRF1 fills the A site, triggering the
release of polypeptide by
hydrolysis of GTP
- Ribosome dissociation and mRNA
release
21. Termination process
- Recognition of stop codon: When the ribosome encounters a stop codon (UAA, UAG, or UGA) in the mRNA,
it signals the end of the protein-coding sequence.
- Binding of release factors: Release factors, specifically eRF1 (eukaryotic release factor 1) and eRF3
(eukaryotic release factor 3), bind to the ribosome at the A site. eRF1 recognizes the stop codon, while
eRF3 aids in the hydrolysis of GTP (guanosine triphosphate) and promotes the dissociation of termination
factors from the ribosome.
- Peptide release: The binding of eRF1 at the stop codon triggers the hydrolysis of the ester bond between
the completed polypeptide chain and the tRNA in the P site. This process is catalyzed by peptidyl
transferase, an enzymatic activity of the ribosome. As a result, the polypeptide is released from the
ribosome.
- Dissociation of ribosome subunits: After peptide release, the ribosome subunits (small and large)
dissociate from each other, along with the mRNA and tRNA molecules.
- mRNA degradation: In eukaryotes, after termination, the mRNA molecule typically undergoes
degradation. This degradation process involves the removal of the poly(A) tail at the 3' end of the mRNA,
which is facilitated by exonucleases. The degradation helps to control gene expression and prevent the
accumulation of unnecessary or faulty mRNA molecules.
22. Post Translational Modification
After translation, the newly synthesized polypeptide may undergo
various modifications, such as folding into its functional conformation,
cleavage of signal peptides or additional amino acids, attachment of
prosthetic groups, or other chemical modification
PTMs play critical roles in regulating protein structure, function,
localization, and stability. Here are some key post-translational
modifications that occur in eukaryotes:
23. Post Translation Modification
Post-translation
modification
Mechanism Function
Protein
phosphorylation
Addition of a phosphate group to an amino acid
residue.
Phosphorylation regulates protein
activity, signaling pathways, enzyme
function, and protein-protein interactions
Protein
glycosylation
Glycosylation involves the attachment of sugar
molecules to specific amino acid residues, such
as asparagine (N-glycosylation) or
serine/threonine (O-glycosylation)
Glycosylation can impact protein folding,
stability, trafficking, and recognition by
other molecules.
Protein
ubiquitination
Binding of a ubiquitin protein to a protein via a
three-step process. This modification is mediated
by a series of enzymes, including E1 activating
enzymes, E2 conjugating enzymes, and E3 ligases
Ubiquitination plays a crucial role in
protein degradation through the
proteasome, as well as in protein
trafficking, signaling, and DNA repair.
Protein
methylation
Addition of a methyl group, most often at lysine
or arginine residues.
Methylation can influence protein-protein
interactions, gene expression, and histone
modification.
Protein
acetylation
Addition of an acetyl group to an N-terminus of a
protein, or at lysine residues.
Acetylation can regulate protein stability,
DNA binding, protein-protein interactions,
and gene expression.
24. CREDITS: This presentation template was created by Slidesgo, and
includes icons by Flaticon, and infographics & images by Freepik
Thanks!
