TRANSLATION
 The
next step in manufacturing a
protein involves translating the mRNA
formed in transcription to a protein
 In
translation, the encoded message is
read, codon by codon, by a ribosome,
and with the presence of transfer RNA
molecules, the ribosome assemble one
amino acid at a time into a polypeptide
chain
Translation:
http://www.youtube.com/watch?v=5bLEDdPSTQ
One wrong letter:
http://www.youtube.com/watch?v=o3yQZp5Rso
WHAT TRANSLATION
ACCOMPLISHES
In translation, information present in the mRNA is
read by the ribosome to synthesize a polypeptide.
TRANSLATION HAS MANY
COMPONENTS..
TRNA
 tRNA
have regions of
base pair, with 4 double
helical segments to form
a clover leaf shape
 At
one tip, has an
segment called an
anticodon
 sequence of 3
nucleotides that
pairs with a
codon from the
mRNA
TRNA
 Example
 Codon:
5’ AGU 3’
 Antidon 3’ UCA 5
 When
tRNA is linked to
its correct amino acid,
it is called:
aminoacyl-tRNA
tRNA Is An Adaptor That Couples Codons and Amino Acids
RIBOSOMES
Carry out protein
synthesis by
translating mRNA
into chains of amino
acids
 Ribosome is made up
of 2 different size
parts called the large
and small ribosomal
sub units
 Each sub unit is made
up of a combination of
rRNA and ribosomal
proteins

RIBOSOMES
Ribsome has special binding
sites that bring together mRNA
and the aminoacyl-tRNA
 3 sites= A,P & E
 A site (amino acyl): where
incoming amino acyl-tRNA
carrying the next amino acid
to be added to the polypeptide
chain, binds to the mRNA
 P Site (peptidyl) : the site
where the tRNA, carrying the
growing peptide chain is
bound
 E Site (exit): exiting tRNA
leaves ribosome

THE PROCESS OF TRANSLATION
HAPPENS IN 3 STEPS:
1. INITIATION
2. ELONGATION
3. TERMINATION
INITIATION





The first amino acyl-tRNA of the new protein
chain becomes bound to the AUG start codon
This is called the initiator methioninetRNA
It forms a complex with the small ribosomal
unit
This complex binds to the mRNA at the 5’ cap
and then moves along the mRNA until it
reaches the first AUG codon
this is the start codon and is recognized by the
anti codon of MET-tRNA
INITIATION
The large ribosomal unit then binds to
complete the ribosome at the end of
initiation
 The initiator MET-tRNA is in the P site
 Correct initiator tRNA-AUG pairing
establishes the correct reading frame;
the series of codons for the polypeptide
that is encoded by the mRNA
 A large and small ribosomal subunits
connect to an mRNA molecule

ELONGATION
This is a 4 step
process
ELONGATION: STEP 1
Begins when the initiator tRNA, with
its attached methionine, becoming
bound to the P site of the ribosomal
unit
ELONGATION: STEP 2
appropriate anti-codon
and amino acid binds to
the codon in the A site
 The amino acid is cleaved
from the tRNA in the P
site and forms a peptide
bond with the amino acid
on the tRNA in the A site
 Peptidyl transferase is
the enzyme that allows
this to happen

E P A
ELONGATION: STEP 3
the ribosome moves along
the mRNA to the next
codon
 the two tRNAs remain
bound to their respective
codons
 An appropriate tRNA
moves into the A site and
steps 2 and 3 are repeated
 After each repeat the empty
tRNA that was in the P site
moves to the E site

ELONGATION STEP 4

the empty tRNA is released from the ribosome
TERMINATION

Translation switches from the elongation to
the termination stage when the A site of a
ribosome arrives at one of the stop codons
(UAA, UAG, or UGA) on the mRNA

Because no amino acid is present at the A site
the polypeptide chain is detached and
ribosomal subunits separate from mRNA
TRANSLATION IN EUKARYOTES AND
PROKARYOTES


In both eukaryotes and
prokaryotes multiple
ribosomes can translate an
mRNA molecule at the same
time, thereby increasing the
production of crucial proteins
Polysome is a complex that
is formed when multiple
ribosomes attach to the same
mRNA in order to facilitate
rapid translation
FROM PROTEIN TO POLYPEPTIDE
The polypeptide that has been assembled by the
ribosome is still not functional
 The protein exists in an inactive state
 Since the shape of the protein defines its function,
the polypeptide chain must be folded into the correct
confirmation
 Enzymes will carry out processes that turn this
polypeptide into its functional shape and join various
polypeptide chains together if needed

REMEMBER THE GENETIC CODE…
These are the words of the genetic language.
Translation Is a
Cyclic, Multistep
Process