This document summarizes the process of translation in prokaryotes. It begins with an introduction to translation occurring in the cytoplasm where ribosomes synthesize proteins using messenger RNA (mRNA). The three main stages of translation are then described in detail: initiation, elongation, and termination. Initiation involves assembly of the ribosome and initiation factors on the mRNA start codon. Elongation is the process of adding amino acids to the growing polypeptide chain through binding of transfer RNA (tRNA) and the actions of elongation factors. Termination occurs when a stop codon is reached and release factors trigger hydrolysis and release of the completed protein. Key components of translation like ribosomes, mRNA, tRNA, and their functions are

1. TRANSLATION IN
PROKARYOTES
Mrs. Praveen Garg
VITS College, Satna

2. INTRODUCTION
 In prokaryotes, translation occurs in the cytoplasm, where the
large and small subunits of the ribosome bind to the mRNA.
 Translation is the process in which ribosomes in
the cytoplasm or endoplasmic reticulum synthesize proteins
after the transcription of DNA to RNA in the cell's nucleus.
The entire process is called gene expression.
 In translation, messenger RNA (mRNA) outside the nucleus,
produce a specific amino acid chain, or polypeptide.
 The ribosome facilitate the binding of complementary tRNA
anticodon sequence to mRNA codons.
 The tRNAs carry specific amino acids that are chained
together into a polypeptide as the mRNA passes through and
is "read" by the ribosome.

3. Various tools used in process of translation.
• mRNA, tRNA, Ribosome, Amino acids, Initiation factor,
elongation factor.

4. Ribosomes:
• It is made up of rRNA and
proteins.
• 70s ribosome occur in
prokaryotic cells.
• It consist of two subunit
smaller (30s) and larger (50s).
• Larger subunit consist of
three site: A site, P site, E site.
• A site: Amino acid
attachment site
• P site: Polypeptide site
• E site: Exit site

5. Transfer RNA (tRNA):
• It contain three structural loops
joined by hydrogen bonding.
• The 3′ end serves as the amino
acid attachment site.
• The center loop encompasses the
anticodon.
• The anticodon is a three-base
nucleotide sequence that binds to
the mRNA codon, which is
complementary to anticodon.
• Transfer RNA brings
or transfers amino acids to the
ribosome.

6. • Translation process complete in three phases:
• Initiation: The ribosome assembles around the target mRNA.
The first tRNA is attached at the start codon.
• Elongation: The tRNA transfers an amino acid to the tRNA
corresponding to the next codon. The ribosome then moves
the next mRNA codon to continue the process, creating an
amino acid chain.
• Termination: When ribosome reached in stop codon, it
releases the polypeptide.

7. INITIATION
• Ribosomes initiate translation on mRNAs during transcription.
Hence, transcription and translation are cellular processes.
• This is the first phase of translation. Start or initiation codon
[AUG] is responsible for initiation of translation process.
• During initiation process, the Shine-Dalgarno (SD) sequence
present in mRNAs interacts with the anti-SD sequence of the 16S
rRNA, and the initiation codon is adjusted in the P-site of the
ribosome.
• Before initiation process, activation of amino acid is necessary.

8. Activation of amino acid
• In activation, correct amino acid is covalently bonded with
correct tRNA.
• It is required for translation to proceed.
• The amino acid is joined by its carboxyl group to 3’OH group of
tRNA by an ester bond with the help of ATP.
• When tRNA is linked with amino acid, it is termed as charged.
• In both reaction, amino-acyl tRNA synthetase enzyme catalyze
these reaction.
Amino acid + ATP Amino acid -AMP complex (Activated amino acid)
Amino acid AMP complex + tRNA Amino acyl tRNA complex

9. • Initiation of translation in prokaryotes involves the assembly of
the components of the translation system which are:
 the two ribosomal subunits (small and large),
 the mRNA to be translated,
 the first (formyl) aminoacyl tRNA (the tRNA charged with the
first amino acid),
 GTP (as a source of energy),
 three initiation factors (IF 1, IF 2 and IF 3) which help the
assembly of the initiation complex.

10. • Translation begins with the binding of the small ribosomal
subunit to a specific sequence on the mRNA chain.
• IF1 (initiation factor 1) blocks the A site to ensure that the Met-
tRNA can bind only to the P site.
• No other aminoacyl-tRNA can bind in the A site during initiation.
• IF3 dissociate the two subunits of ribosomes and blocks the E site
and prevents the two subunits from associating.
• IF2 is a small GTPase which binds fmet-tRNAf
Met and helps its
binding with the small ribosomal subunit.

11.  16sRNA recognize the Shine Dalgarno sequence present in
mRNA and bind with it.
 This process helps to correctly position the ribosome onto the
mRNA so that the P site is directly on the AUG initiation codon.
 IF3 helps to position fMet-tRNAf
met into the P site, such that
fMet-tRNAf
met interacts with the mRNA initiation codon (AUG).
 In the last step of initiation, large ribosomal subunit joins the
complex causing the dissociation of initiation factors.

13. ELONGATION
• Elongation begins after the formation of the initiation complex.
• Elongation means the length of polypeptide chain is increasing.
• Elongation of the polypeptide chain involves addition of amino
acids to the carboxyl end of the growing chain.
• The growing protein exits the ribosome through the polypeptide.
• This is energy dependent process.
• This process complete in three steps:
 Binding of amino acyl tRNA to A site.
 Transpeptidation
 Translocation
• There are three elongation factor involve:
 EF-Tu, EF-Ts, EF-G

14. Binding of amino - acyl tRNA to A site:
• Elongation starts when the fmet-tRNA enters the P site, causing a
conformational change which opens the A site for the new aminoacyl-
tRNA to bind.
• This binding is facilitated by elongation factor-T4 (EF-Tu), a small
GTPase.
• The P site contains the peptide chain of the protein to be encoded and
the A site has the next amino acid to be added to the peptide chain.
Peptide bond formation:
• The growing polypeptide connected to the tRNA in the P site is
detached from the tRNA in the P site and a peptide bond is formed
between the last amino acids of the polypeptide and the amino acid
still attached to the tRNA in the A site.
• This process, known as peptide bond formation, is catalyzed by a
ribozyme, peptidyltransferase. Now, the A site has newly formed
peptide, while the P site has an unloaded tRNA (tRNA with no amino
acids).

15. Translocation:
• In the final stage of elongation, translocation, the ribosome
moves 3 nucleotides towards the 3′ end of mRNA.
• Since tRNAs are linked to mRNA by codon-anticodon base-
pairing, tRNAs move relative to the ribosome taking the nascent
polypeptide from the A site to the P site and moving the
uncharged tRNA to the E exit site.
• This process is catalyzed by elongation factor G (EF-G).
• The ribosome continues to translate the remaining codons on
the mRNA as more aminoacyl-tRNA binds to the A site, until the
ribosome reaches a stop codon on mRNA(UAA, UGA, or UAG).

18. TERMINATION
• This is the last phase of translation.
• Termination occurs when one of the three termination codons
moves into the A site.
• These codons are not recognized by any tRNAs.
• They are recognized by proteins called release factors, namely
RF1 (recognizing the UAA and UAG stop codons) or RF2
(recognizing the UAA and UGA stop codons).
• These factors trigger the hydrolysis of the ester bond in peptidyl-
tRNA and the release of the newly synthesized protein from the
ribosome.
• A third release factor RF-3 catalyzes the release of RF-1 and RF-2
at the end of the termination process.

20. Thank you