7.3 Translation
Essential Idea 2.7: Genetic information in DNA can be accurately copied and can be translated to make the
proteins needed by the cell
Essential Idea 7.3: Informational transferred from DNA to mRNA is translated into an amino acid sequence
What is Translation?
 Translation is the ___________ of ___________________(polymer of amino acid)
_______________________
 Translation happens in the cytoplasm / ER on a structure called ribosomes
 Ribosomes are made up __________ (ribosomal RNA) molecules and __________
Transcription  Translation
1. After genes are ____________ into mRNA and ____________ into _______ mRNA,
2. These mRNA will exit the nucleus and bind to the ________ __________ of the ribosomes
3. Ribosomes has a large subunit and a small subunit which helps to bind the _________, _________ and
amino acids together and ____________ the formation of _________ between the
___________________
Ribosomes
7.3.S3 The use of molecular visualisation software to analyse the
structure of eukaryotic ribosomes and tRNA molecules.

Recall: ribosomes in prokaryotes (70s) and in Eukaryotes (80s)

Ribosomes are made up of
a. protein – for ________________
b. ribosomal RNA – for ________ ____________

They have 2 subunits
a. __________ subunit (30s) binds to the ___________
b. ______ subunit (50s) have 3 ________ _________ sites
c. ___ (exit) site,___ (peptidyl) site, ___ (aminoacyl) site
Structure of tRNA
 Have sections that become ______ ___________ by ________ __________
 _______ base – ______________ (3 bases – attached to ________) which is part of the bottom loop
 Two other loops - associate with ______________ (T arm) & tRNA _____________ _______ (D arm)
 Base sequence __________ at the ________ end which forms site for _____________ to
__________ _____________ – called the ____________ loop/stem
tRNA activating enzyme
7.3.A1 tRNA-activating enzyme illustrate enzyme-substrate specificity
and the role of phosphorylation
 tRNA molecule binds to a __________________ amino acid by
_________________________________________________
 20 different types of tRNA activating enzyme – the enzyme’s
_________ __________ is ___________ to each 20 _________
____________ and specific to the correct __________ _________
(may recognise multiple tRNA due to _________________)
 This process uses __________ for energy, main function of ATP is to
___________ the _______ ____________ _______ to tRNA as
________ from this __________ is later used to _________ amino
acid (____________ bond) during formation of the _______________ chain
Step-by-step process
1. Specific ________ ________ & ____________ attached to active site of enzyme
2. ATP _____________ (break bond and release two phosphate) and ___________ amino acid
3. By forming a ________ _________ ____________ between _______________ and _________
(adenosine monophosphate – originally from ATP)
4. The high energy bond is transferred to ___________ ____________ the activated amino acid to
tRNA & AMP is released
5. tRNA is ‘_______________’ and ready to use
The GENETIC CODE – CODONS
2.7.U6 The amino acid sequence of polypeptides is determine by mRNA according to the genetic code
2.7.U7 Codons on three bases on mRNA correspond to one amino acid in polypeptide





There are four different bases and
20 different type of amino acids
So for the bases to code for the
amino acids, we use a t_______
b_____ code – called c________
Three combination of bases –
codes for a certain type of
_________ ____________
The ______ of these codons on
the __________ determines the
amino acid ____________ of the
polypeptides
Note* there is also a STOP &
START codon
KEY Features of the Genetic Code
 The __________ __________ is _____________ - All living organisms uses the ________ triplet
base ___________ (meaning this has evolved at the origin of life)
 In very limited organisms, some codons have different meaning, which raised some hypothesis that
genetic code might not be universal, or that codons have occurred after the origin of life
 The code is ‘__________________’ – meaning that there are m_______ than o_____ c________
that codes for an amino acid
o The degeneracy usually (not always) happens in the t_______ b________ p_________
o This also allows for ‘s__________ m______________ – meaning a mutation of the third
base will not affect the production of protein
Translation from mRNA codon
• In order to translate an mRNA sequence into a polypeptide chain, it is important to establish the
correct r____________ f____________
• An open reading frame starts with __________ (_____________ codon) and will continue in triplets
to a _____________ codon (UAA, UAG, UGA)
Codons on mRNA; Anti-codons on tRNA
2.7.U8 Translation depends on complementary base pairing between codons on mRNA and anticodons on
tRNA
•
•
__________________ (transfer RNA) has an ______________ that binds c_______________ to the
___________ of the mRNA (through base pairing) and each tRNA carries the ___________
_________ the corresponding triplet base codon on mRNA
So as the ribosome ‘reads’ the mRNA from ________ to ____________direction, the tRNA with the
complementary anti-codon to the mRNA will bind to the ribosome in sequence
Initiation of Translation
7.3.U1 Initiation of translation involves assembly of components that carry out the process
1. ___________ binds to _________ ribosomal
subunit
2. tRNA molecule carrying ___________ binds
to ’start’ codon ____________ at the ______ site
3. ____________ ribosomal unit then bind to the
____________ ribosomal unit
4. The next codon _________ another ________ to
bind to the __________ site
Elongation of Translation
7.3.U2 Synthesis of the polypeptide involves a repeated cycle of events
5. _____________ _______ (condensation reaction) form between ________ _______ in ____ & _____ site
6. The first amino acid form P site is now _________________ attached to the amino acid from A site and
the first tRNA is ________________ (no amino acid)
7. As the ribosome moves along the mRNA (5’  3’), the deacylated tRNA moves from P to ____________
site and is _______________.
8. While the tRNA carrying the growing _________ _______ __________moves from _____ to _______ site
9. The next tRNA molecule that binds to the complementary base in the empty _______ site
10. This process is _________________ until a STOP codon is reached
Termination of Translation
7.3.U3 Disassembly of components follows termination of translation
•
•
When stop codon is reached, a
r____________ f_________ binds
to the _____ site that signals
translation to stop (no tRNA for
STOP codon)
_____________ & _________ is
released and ribosome
d_____________ into two independent subunits
Free Ribosomes
7.3.U4 Free ribosomes synthesize proteins for use primarily
within the cell
•
•
•
•
In Eukaryotes, ribosomes are separated from DNA by
the nucleus
Transcription happens in the __________ but
_____________ happens in the _________ (fluid in
cytoplasm) or the ______________ _________
After transcription, mRNA is transported from the
nucleus and this transport requires
m___________________ of mRNA (eg: ____
___________ & addition of ________ t____ at 3’)
Proteins destined for use in the ____________,
_______________ and _______________ are
synthesized by ________ ______________ in the _________________
ER Bound ribosomes
7.3.U5 Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes
• Proteins that are used in the _______, _________ ___________, ____________, _________
_____________ or _____________ outside the ___________ are synthesized by ribosomes
_________ to the __________
• Whether the ribosome is bound to the ER or free in the cytoplasm depends on the _________
_________________ on the _____________ being translated
• The _________ _____________ is in the _________ part of the polypeptide and it can bind to a
s___________ r______________
p______________ that stops
_____________ until it binds to a
________________ on the ________surface
• Once this happen, translation then
continue and the polypeptide chain
_____________ into the ER as it is
being translated
Prokaryotes – transcription & translation
7.3.U6 Translation occur immediately after transcription in prokaryotes due to absence of nuclear
membrane
•
•
•
•
In prokaryotes, ribosomes can start ________________
can _________ ____________ even while the rest of the
mRNA is being transcribed from the DNA template
This is because there is ______ ___________
__________________ ______________ it
And possible because both _______________ and
_____________ occur in the ____ to ____ direction
No modification of mRNA in prokaryotes
Polysomes (many ribosomes)
7.3.S1 Identification of polysomes in electron micrographs of prokaryotes and eukaryotes
•
•
•
•
Polysomes = _____________ ______________ attached to a ________ __________ strand
Visible under the electron microscope
In prokaryotes, polysomes can be seen associated with ___________ strand
In eukaryotes, polysomes occur in ____________ and next to _____________
In this eukaryotic polysome, the 5’ end is on the
left as it has shorter polypeptide chain where
the ribosomes have just started translating
while the 3’ end is on the right where long
chains of polypeptides have formed.
Primary structure – chain of amino acid
7.3.U7 The sequence and number of amino acid in the polypeptide is the
primary structure
• Polypeptide – _________ of __________ with __________
_____________ and _______________
• With 20 types of amino acid, combined in any sequence and in any
numbers brings a huge diversity of polypeptide
• Primary structure controls all subsequent levels of protein
organisation because it determines the nature of the interactions
between R groups of different amino acids
Secondary Structure
7.3.U8 The secondary structure is their formation of alpha helices and beta pleated sheets stabilised by
hydrogen bonding
•
•
•
•
•
Chain of amino acid have ___________ covalent bonds in its ________________
due to _________ from _________ grp & ________ from ________________ grp of
__________________________ amino acids
Hydrogen bonds can form between Hydrogen of amine group of one amino acid to oxygen of
carboxyl group of another amino acid along the chain
• Form either ________________ or ____________________
Polypeptide coil / fold and hydrogen bonds provide ____________ ________________
Most fibrous proteins have secondary structure (eg: collagen & keratin)
Tertiary Structure
7.3.U9 The tertiary structure is the further folding of
the polypeptide stabilised by interaction between R
groups
• Further bonds formed between the
_____________ side chains & surrounding
water molecule ___________ the proteins into
a complex ______________
• Tertiary ____________ maybe important for
______________ of protein (eg: specific active
site shape for enzymes)
• Eg: ________________, _________________,
___________________, _________________
• This structure is common in _____________
proteins
Quaternary structure
7.3.U10 The quaternary structure exists in proteins with more than one polypeptide chain
• Forms when _________________ ________________ interact together (haemoglobin is composed
of four polypeptide chains)
• Or interact with ___________________ prosthetic group (eg: Fe – haem group in haemoglobin)
• Can be fibrous or globular proteins
Shape
Role
Solubility
Reason for
insolubility/
solubility
Sequence
Stability
Examples
Fibrous Protein
Globular protein
Hydrophobic R groups are exposed as
it form long strands
Hydrophobic R groups can be folded into core
of molecule and away from surrounding water
molecules
7.3 Translation
Essential Idea 2.7: Genetic information in DNA can be accurately copied and can be translated to make the
proteins needed by the cell
Essential Idea 7.3: Informational transferred from DNA to mRNA is translated into an amino acid sequence
What is Translation?
 Translation is the synthesis of polypeptide (polymer of amino acid) on ribosomes
 Translation happens in the cytoplasm / ER on a structure called ribosomes
 Ribosomes are made up rRNA (ribosomal RNA) molecules and proteins
Transcription  Translation
4. After genes are transcribed into mRNA and modified into mature mRNA,
5. These mRNA will exit the nucleus and bind to the small subunit of the ribosomes
6. Ribosomes has a large subunit and a small subunit which helps to bind the mRNA,
tRNA and amino acids together and catalyse the formation of bond between the amino acids
Ribosomes
7.3.S3 The use of molecular visualisation software to analyse the
structure of eukaryotic ribosomes and tRNA molecules.



Recall: ribosomes in prokaryotes (70s) and in Eukaryotes (80s)
Ribosomes are made up of
c. protein – for stability
d. ribosomal RNA – for catalytic activity
They have 2 subunits
d. Small subunit (30s) binds to the mRNA
e. Large subunit (50s) have 3 tRNA binding sites
f. E (exit) site, P (peptidyl) site, A (aminoacyl) site on large
subunit
Structure of tRNA
 Have sections that become double stranded by base pairing
 Triplet base – anticodon (3 bases – attached to mRNA) which is part of the bottom loop
 Two other loops - associate with ribosomes (T arm) & tRNA activating enzyme (D arm)
 Base sequence CCA at the 3’ end which forms site for attaching to amino acid – called the acceptor
loop/stem
tRNA activating enzyme
7.3.A1 tRNA-activating enzyme illustrate enzyme-substrate specificity
and the role of phosphorylation



tRNA molecule binds to a specific amino acid by tRNA-activating
enzyme
20 different types of tRNA activating enzyme – the enzyme active
site is specific to each 20 amino acids and specific to the correct
tRNA molecule (may recognise multiple tRNA due to degeneracy)
This process uses ATP for energy, main function of ATP is to transfer
the high energy bond to tRNA as energy from this bond is later used
to linked amino acid (peptide bond) during formation of the
polypeptide chain
Step-by-step process
6. Specific amino acid & ATP attached to active site of enzyme
7. ATP hydrolyse (break bond and release two phosphate) and activate amino acid
8. By forming a high energy bond between amino acid – AMP (adenosine monophosphate – originally
from ATP)
9. The activated amino acid is then covalently bonded to tRNA & AMP is released
10. tRNA is ‘charged’ and ready to use
The GENETIC CODE – CODONS
2.7.U6 The amino acid sequence of polypeptides is determine by mRNA according to the genetic code
2.7.U7 Codons on three bases on mRNA correspond to one amino acid in polypeptide





There are four different bases and
20 different type of amino acids
So for the bases to code for the
amino acids, we use a triplet base
code – called codons
Three combination of bases –
codes for a certain type of amino
acid
The order of these codons on the
mRNA determines the amino
acid sequence of the
polypeptides
Note* there is also a STOP &
START codon
KEY Features of the Genetic Code
 The genetic code is universal - All living organisms uses the same code (meaning this has evolved
at the origin of life)
 In very limited organisms, some codons have different meaning, which raised some hypothesis that
genetic code might not be universal, or that codons have occurred after the origin of life
 The code is ‘degenerate’ – meaning that there are more than one codon that codes for an amino
acid
o The degeneracy usually (not always) happens in the third base position
o This also allows for ‘silent mutation’ – meaning a mutation of the third base will not affect
the production of protein
Translation from mRNA codon
• In order to translate an mRNA sequence into a polypeptide chain, it is important to establish the
correct reading frame
• An open reading frame starts with AUG (start codon) and will continue in triplets to a termination
codon (UAA, UAG, UGA)
Codons on mRNA; Anti-codons on tRNA
2.7.U8 Translation depends on complementary base pairing between codons on mRNA and anticodons on
tRNA
•
•
tRNA (transfer RNA) has an anti-codon that binds complementarily to the codon of the mRNA and
each carries the amino acid the corresponding amino acid
So as the ribosome ‘reads’ the mRNA from 5’ to 3’ direction, the tRNA with the complementary
anti-codon to the mRNA will bind to the ribosome in sequence
Initiation of Translation
7.3.U1 Initiation of translation involves assembly of components that carry out the process
5. mRNA binds to small ribosomal subunit
6. tRNA molecule carrying methionine binds
to ’start’ codon AUG at the P site
7. Large ribosomal unit then bind to the small
ribosomal unit
8. The next codon signals another tRNA to bind to
the A site
Elongation of Translation
7.3.U2 Synthesis of the polypeptide involves a repeated cycle of events
5. Peptide bond (condensation reaction) form between amino acid in A & P site
6. The first amino acid form P site is now covalently attached to the amino acid from A site and the first
tRNA is deacylated (no amino acid)
7. As the ribosome moves along the mRNA (5’  3’), the deacylated tRNA moves from P to E site and is
released.
8. While the tRNA carrying the amino acid chain moves from A to P site
9. The next tRNA molecule that binds to the complementary base in the empty A site
10. This process is repeated until a STOP codon is reached
Termination of Translation
7.3.U3 Disassembly of components follows termination of translation
•
•
When stop codon is reached, a
release factor binds to the A site
that signals translation to stop (no
tRNA for STOP codon)
Polypeptide & mRNA is released
and ribosome disassembled into
two independent subunits
Free Ribosomes
7.3.U4 Free ribosomes synthesize proteins for use
primarily within the cell
•
•
•
•
In Eukaryotes, ribosomes are separated from DNA
by the nucleus
Transcription happens in the nucleus but
translation happens in the cytosol (fluid in
cytoplasm) or the endoplasmic reticulum
After transcription, mRNA is transported from the
nucleus and this transport requires modification of
mRNA (eg: 5’ capping & addition of poly-A tail at 3’)
Proteins destined for use in the cytoplasm,
mitochondria and chloroplasts are synthesized by
free ribosomes in the cytoplasm
ER Bound ribosomes
7.3.U5 Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes
•
•
•
•
Proteins that are used in the ER, Golgi apparatus, lysosomes, plasma membrane or secreted outside
the cell are synthesized by ribosomes bound to the ER
Whether the ribosome is bound to the ER or free in the cytoplasm depends on the signal sequence
on the polypeptide being translated
The signal sequence is in the initial
part of the polypeptide and it can
bind to a signal recognition
proteins that stops translation
until it binds to a receptor on the
ER surface
Once this happen, translation then
continue and the polypeptide chain
grows into the ER as it is being
translated
Prokaryotes – transcription & translation
7.3.U6 Translation occur immediately after transcription in prokaryotes due to absence of nuclear
membrane
•
•
•
•
In prokaryotes, ribosomes can start translation can
occur immediately even while the rest of the mRNA
is being transcribed from the DNA template
This is because there is no nuclear membrane
separating it
And possible because both translation and
transcription occur in the 5’ to 3’ direction
No modification of mRNA in prokaryotes
Polysomes (many ribosomes)
7.3.S1 Identification of polysomes in electron micrographs of prokaryotes and eukaryotes
•
•
•
•
Polysomes = multiple ribosomes attached to a single mRNA molecules
Visible under the electron microscope
In prokaryotes, polysomes can be seen associated with DNA strand
In eukaryotes, polysomes occur in cytoplasm and next to ER
In this eukaryotic polysome, the 5’ end is on the
left as it has shorter polypeptide chain where
the ribosomes have just started translating
while the 3’ end is on the right where long
chains of polypeptides have formed.
Primary structure – chain of amino acid
7.3.U7 The sequence and number of amino acid in the polypeptide is the
primary structure
• Polypeptide – chain of amino acid with specific sequence and length
• With 20 types of amino acid, combined in any sequence and in any
numbers brings a huge diversity of polypeptide
• Primary structure controls all subsequent levels of protein
organisation because it determines the nature of the interactions
between R groups of different amino acids
Secondary Structure
7.3.U8 The secondary structure is their formation of alpha helices and beta pleated sheets stabilised by
hydrogen bonding
•
•
•
•
•
Chain of amino acid have polar covalent bonds in its back bone
due to N--H from amine grp & C=O from carboxyl grp of non-adjacent amino acids
Hydrogen bonds can form between amine group of one amino acid to carboxyl group of another
amino acid along the chain
• Form either ⍺ - helix or β – pleated sheet
Polypeptide turn / fold and hydrogen bonds provide structural stability
Most fibrous proteins have secondary structure (eg: collagen & keratin)
Tertiary Structure
7.3.U9 The tertiary structure is the further folding of
the polypeptide stabilised by interaction between R
groups
• Further bonds formed between the R group
side chains & surrounding water molecule folds
the proteins into a complex 3D structure
• Tertiary structure maybe important for function
of protein (eg: specific active site shape for
enzymes)
• Eg: H-bonds, disulphide bonds, ionic bonds and
hydrophobic interactions
• This structure is common in globular proteins
Quaternary structure
7.3.U10 The quaternary structure exists in proteins
with more than one polypeptide chain
• Forms when multiple polypeptides interact together (haemoglobin is composed of four polypeptide
chains)
• Or interact with inorganic prosthetic group (eg: Fe – haem group in haemoglobin)
• Can be fibrous or globular proteins