Download Chapter-Translation (Prokaryotes)

Chapter-Translation (Prokaryotes)
Paper: Molecular Biology
Lesson: Translation (Prokaryotes)
Author Name: Dr. Hardeep Kaur
College/ Department: Ramjas College,
Department of Zoology , University of Delhi
1
Process of Protein Synthesis in Prokaryotes
1. Introduction:
The phenomenon of interpretation of the genetic information contained in the mRNA and
converting it into a sequence of amino acids joined by peptide linkages to form a protein
molecule, has always intrigued molecular biologists. This process of translation is highly
conserved among all organisms and is a process that utilizes the maximum energy resources of a
cell. There is interplay of more than hundred different proteins and RNAs to yield one linear
strand of protein. There is almost no affinity between certain aromatic amino acids and the three
nucleotide codon structure of the information present on mRNA. Similarly the attraction between
hydrophobic side chains of certain amino acids and the mRNA is equally lacking. Hence it
became imperative, that an adaptor molecule might play a significant role in transferring
information from mRNA to the correct amino acid. Francis H Crick in 1955 established the role
of tRNA. The fact that ribosome plays an important role in this process was also established. The
process of translation therefore could be described as a bigger challenge than transcription in
transferring information. In simplest words, it may be described as the process involving transfer
of information from the genetic codes of mRNA to the sequence of amino acid forming a
polypeptide or protein molecule. In prokaryotes the process of translation is a continuous process
with both transcription and translation occurring simultaneously in the cytoplasm.
For animation on Translation kindly visit-https://youtu.be/5bLEDd-PSTQ
2. Ribosome Structure and Assembly:
Ribosomes are important cellular organelles that are involved in the interaction of all molecules
of protein synthesis in an orderly manner. They were first observed in the midst of 20th Century
by Romanian scientist George Emil Palade. Palade observed them under electron microscope and
recognized them as dense particles. Ribosomes change the instructions found in messenger RNA
into the strings of amino-acids that form polypeptides or proteins.
2
Interesting Facts-
George Emil Palade, a Romanian-American cell biologist, was described as "the most influential
cell biologist ever"; in 1974 he was awarded the Nobel Prize in Physiology and Medicine, together
with Albert Claude and Christian de Duve, for his innovations in electron microscopy and cell
fractionation.
2.1 Structure: Prokaryotic ribosome is a spherical particle of 20nm diameter and is made up of a
large and a small subunit. It sediments in sucrose gradients with a sedimentation coefficient of
70S and has 30S and 50S subunits (Fig. 1). Ribosomes can exist freely in the cytoplasm or they
may be attached to endoplasmic reticulum to give it a rough surface. Ribosomes make up the
large part of cells in many species for example in E.coli, they almost occupy 1/4th of cell mass. In
fact ribosomes form the backbone for many molecules during the process of protein synthesis.
The ribosomes on assembly can have many small grooves or tunnels. These are the active sites
dedicated to specific tasks during protein synthesis. During the process of translation of mRNA, a
number of ribosomes attaches to one mRNA molecule, forming polyribosome, also called
polysome. A single mRNA molecule can hence be translated by several ribosomes at the same
time. The mRNA is present in the gap between the two ribosomal subunits. This results in
protection of a stretch of about 25 nucleotides of the mRNA from ribonuclease activity.
3
Fig.1. Prokaryotic ribosome-Large (green) and small (red) subunits
The major components of ribosomes are 65% rRNA and 35% ribosomal proteins. The positive
protein charges of ribosomes are not sufficient to balance the many negative charges in the
phosphates of the RNA and therefore ribosomes are strongly negative and bind cations and basic
dyes. Ribosomal RNA (rRNA) generally represents more than 80% of RNA present in cells.
Prokaryotic ribosomes are mainly composed of three rRNA molecules-16S rRNA in small
subunit (SSU) and 23S and 5S in large subunit (LSU). The ribosomal RNAs bear secondary
structures with more than 2/3rd of it being in the form of double stranded and helical in nature.
The resultant double stranded regions hence form hairpin loops to which the ribonucleoproteins
get bound. The ribosomal RNA also participates in the process of protein synthesis. The 3'
terminal of the 16S rRNA in the small subunit gets attached to a distinctive sequence on the 5'
terminal of mRNA. This sequence is called the Shine-Dalgarno sequence, which helps in the
recognition of the starting point by the 30S subunit (Fig.2).
4
Fig. 2. Shine-Dalgarno Sequence in mRNA
A ribosome has three sites where binding of various components of protein synthesis takes place.
These are named as A, P, and E sites (Fig.3).

The aminoacyl-tRNA (t-RNA bound to its specific amino acid) binds to A site in the
ribosome.

The amino (NH2) group of the aminoacyl-tRNA present on the A site now attacks the ester
linkage of peptidyl-tRNA that is present on the P site and contains the last amino acid of
the growing chain. This leads to the formation of a new peptide bond, a reaction that is
catalyzed by peptidyl transferase.

The tRNA that was carrying the last amino acid is now pushed to the E site and what used
to be the aminoacyl-tRNA now becomes peptidyl-tRNA after translocation.
Multiple ribosomes can consecutively translate a single mRNA as will be discussed later in the
chapter.
5
Fig. 3. Role of Ribosomes in Protein Synthesis-A, P and E site
http://www.keywordpicture.com
2.2 Ribosomal Proteins
The E.coli ribosome contains 21 proteins in the small subunit (named in order of decreasing size
S1 to S21) and 34 in the large (L1 till L34). L26 was later found to be similar to S20; L7 is the
acetylated L12 and L8 is a complex formed by L10 and L7 so in all there are 31 proteins present in
the larger subunit. The molecular weights of these proteins range from 7000 to 32000 Da. Most of
them are rich in basic amino acids. In E.coli, the ribosomal proteins can be dissociated from the
ribosome and then added back to reconstitute active particles. The complete assembly of
ribosome from the naked RNA and proteins demonstrates the principle of self assembly. The
regulation of synthesis of ribosomal proteins takes place at the level of translation.
3. Transfer RNAs: They are small RNAs that serve as molecular adaptors during protein
synthesis. Transfer RNA transcription occurs by RNA Polymerase III and like most other
RNA, tRNA is processed from a longer precursor into its final form. Post transcriptional
processing includes removal of 5’ and 3’ extensions, methylation of some bases, terminal
addition of CCA etc. Each tRNA bears a clover-leaf like structure. They all seem to have
similar sequence of 73 to 93 nucleotides. The salient feature of tRNA structure consists of the
following (Fig.4):
a) A 5'-terminal end containing phosphate group.
6
b) The 3'end always terminates with CCA tail which is a Cytosine-Cytosine-Adenine sequence,
wherein the 3’ hydroxyl of the ribose of the adenine is the point of attachment to amino acid
by aminoacyl tRNA synthetases, to form aminoacyl-tRNA. In prokaryotes, this sequence
(CCA) is generally added during processing of tRNA. It is an important sequence for the
correct recognition of tRNA by enzymes and plays an important role in translation.
c) The acceptor stem that consists of 7- to 9-base pair sequence involving base pairing of the
5'-terminal nucleotide with the 3'-terminal nucleotide which contains the CCA 3'-terminal
group.
d) The D arm is a 4- to 6-bp stem ending in a loop that often contains dihydrouridine.
e) The anticodon arm is a 6-bp stem whose loop contains the anticodon. The tRNA 5'-to-3'
primary structure contains the anticodon but in reverse order, since 3'-to-5' directionality is
required to read the mRNA from 5'-to-3'.
f) The T arm is a 4- to 5- bp loop which contains the sequence TΨC (where Ψ is pseudouridine).
g) Modified bases occur at several places in tRNA molecules.
h) The first anticodon base is mostly modified to inosine (derived from adenine), which lack the
amino group on the purine ring, and thus leads to degeneracy of the code (Wobble
hypothesis). Some tRNAs therefore recognize more than one codon. There is an isoacceptor
tRNA family for each amino acid.
The anticodon of the tRNA hydrogen bonds with a codon triplet in the mRNA and has the
complementary amino acid attached to one of its ends (Fig. 4). Faithful protein synthesis depends
on the correct charging of the amino acid- tRNAs by specific aminoacyl tRNA synthetase.
7
Fig.4. Clover Leaf structure of tRNA
"TRNA-Phe yeast en" by Yikrazuul - Own work.
Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/
Interesting Facts-
In 1965, Robert Holley deciphered the complete sequence of alanyl- tRNA after working tirelessly
for “seven” years on it. Holley was awarded the Nobel8 Prize in Physiology or Medicine in 1968 for
this discovery
3.1 Charging of t-RNA
The aminoacylation of tRNA involves two steps (Fig. 5)
1. Selection of correct amino acid by the amino-acyl-tRNA synthetase for incorporation into
aminoacyl-tRNA
2. Selection of accurate tRNA in response to an mRNA codon, in ribosomes
Each amino acid has specific aminoacyl tRNA synthetase that triggers the carboxyl group of that
amino acid for covalent bonding with adenylic acid residue of CCA end of tRNA. Therefore
aminoacyl synthetase has two sites, one to recognize right amino acid and the other to recognize
right tRNA.
AA + ATP
AA-AMP + P-P
Aminoacyl
synthetase
AA-AMP + tRNA
AA-tRNA +AMP
Aminoacyl
synthetase
Fig.5. Charging of tRNA molecule
9
There are two types of aminoacyl tRNA synthetase:

Type I has two conserved sequence motifs. It is generally monomeric or dimeric protein.
It leads to aminoacetylation of the adenine residue present at the terminal position in
tRNA at 2'-OH position.

Type II has three conserved sequence motifs. It is generally dimeric or tetrameric and
leads to aminoacetylation of the adenine residue present at the terminal position in tRNA
at 3'-OH position.
Both types of aminoacyl-tRNA synthetases however are multidomain proteins.
4. Process of Translation
Translation can be categorized into
4.1 Initiation
4.2 Elongation
4.3 Termination
Initiation involves binding of a ribosome to mRNA. Elongation involves repeated addition of
amino acids and termination involves release of the new polypeptide chain. Sets of accessory
proteins assist the ribosomes in each of the three stages. Translation requires the use of energy by
the cell which is provided by hydrolysis of GTP and ATP. GTP is used for ribosome movement
and in binding of accessory factors. ATP is used to charge tRNAs and in removing secondary
structure from mRNAs. Upto 90% of ATP produced in a bacterium is used for translation. One
peptide bond formation during prokaryotic protein synthesis utilizes two GTP and one ATP
molecules.
4.1 Initiation: The process of initiation in prokaryotes is much different from that in eukaryotes.
This is due to the dissimilar nature of mRNA in both prokaryotes and eukaryotes.
a) Binding of Small Ribosomal Subunit to mRNA-Ribosomes are present as separate large
and small subunits when they are not engaged in translation. The binding of the small
subunit of the ribosome to the mRNA marks the first step of translation process.
Translation starts at the sequence AUG. Upstream of AUG, the small subunit of ribosome
binds at a particular point to mRNA. In prokaryotes, this is known as the Shine-Dalgarno
sequence (5’AGGAGGU3’) that is found near the start of mRNA. After binding to this
10
sequence, the small subunit of ribosome now drifts in a 3’ direction along the mRNA until
it hits upon AUG, about 10 nucleotides downstream.
b) Formation of Initiation Complex-In bacteria, the first amino acid on the mRNA is
different as it has an addition of a formyl (-CHO) group to one of the hydrogens of the
amino group. This obstructs the amino group, thus preventing it from forming a peptide
bond. In this way it ensures that polymerization of the polypeptide can only occur in the
amino to carboxy direction. The mRNA, the small ribosomal subunit and tRNAfmet
together forms the Initiation Complex. Two types of tRNAs recognize AUG and carry
methionine. One is used for initiation (tRNAfmet) and the other recognizes internal AUGs.
Only the initiator tRNA is capable of binding to the initiation complex (Fig.6). Since Nformyl methionine is the initiator amino acid, so it can be thought that almost all
prokaryotic proteins will have formyl group in the beginning. This is not true as there is an
enzyme “deformylase” that cleaves this formyl group from the amino terminal of newly
synthesized protein in prokaryotes.
Fig.6. Initiation Complex in Prokaryotic Translation
http://www.dayshare.org/thelawofscience/translation-12283158
11
c) Role of Initiation Factors- Certain accessory proteins called “Initiation factors” are also
required for initiation. IF1, IF2 and IF3 are the three initiation factors in bacteria (Fig.7).
Each factor has a specific role to play in the initiation process.

The process of Initiation starts with the binding of IF1 and IF3 to the small
ribosomal subunit. IF1 ensures that tRNA does not get bound to A site of the small
ribosomal subunit.

Role of IF3 is to ensure that the large subunit does not bind prematurely before
mRNA has bound. In fact IF3 gets bound to the small ribosomal subunit in the
previous cycle of translation itself and hence ensures dissociation of ribosome into
its large and small subunits.

IF2 is actually a GTPase. It gets bound to GTP and together they bind to the small
subunit. This assists in binding of the initiator tRNA. Now the small subunit binds
to the mRNA and finds the AUG codon where the translation has to start. The
initiator tRNA carrying methionine binds to the complex and IF3 is released. This
symbolizes the end of initiation.
Large ribosomal subunit now binds to the initiation complex to form a complete ribosome.
Fig. 7. Role of Initiation Factors in Prokaryotic Translation Initiation
12
4.2 Elongation: Unlike initiation, the process of translation is highly conserved in both
prokaryotes and eukaryotes. Once the ribosome assembly has taken place along with the initiator
tRNA at P site, the protein synthesis commences as follows-
a) Binding of incoming aminoacyl tRNA at A site- The next step involves the release of
IF1 and IF2 and GTP hydrolysis takes place. The complete ribosome now has two binding
sites for tRNA molecules. The tRNAfmet base paired to AUG occupies the Peptidyl site or
the P-site. The second site is the A site or aminoacyl site and is located over the second
codon. Elongation commences when a tRNA enters the A site. This tRNA now base pairs
with the second codon (Fig.8).
b) Formation of Peptide Bond- Once both the sites in the ribosome are occupied by charged
tRNAs, the attached amino acids are placed in close contact and peptide bond can form
between the carboxyl group of the methionine and amino group of the second amino acid.
The reaction is catalyzed by an enzyme peptidyl transferase. Peptidyl transferase works in
concurrence with another enzyme, tRNA deacylase, which breaks the link between
methioinine and its tRNA after formation of the peptide bond.

Certain elongation factors or accessory proteins are also required for elongation. In
prokaryotes, two elongation factors EFTu and EFTs are involved (Fig. 9).

EFTu is involved with entry of a tRNA in to the A site. EFTu binds charged
tRNAs in association with GTP. Following entry to the A site, the GTP is
hydrolyzed and EFTu is released bound to GDP. In this state, EFTu has least
affinity for aminoacyl tRNA. On its own EFTu associated with aminoacyl tRNA
does not have any GTPase activity. This actually gets activated when EFTu gets
associated with the same domain on large ribosomal subunit (factor binding center)
that also activates IF2 GTPase. Again this can take place only if the correct codonanticodon binding has taken place. Hence this becomes a very important regulatory
step of prokaryotic protein synthesis

Before another tRNA can bind, EFTu must be regenerated with the help of EFTs.
First EFTs displaces GDP by binding to EFTu, a new molecule of GTP then
combines to EFTu and releases EFTs.
13
+EFTs
EFTu/GDP
+GTP
EFTu/EFTs
-GDP
EFTu/GTP
-EFTs
c) Translocation-Following peptide bond formation, translocation occurs and the ribosome
shifts to the following codon. The newly formed protein chain with two amino acids is
bound to the second tRNA. It now moves into the P site expelling the uncharged tRNA
and the A site becomes free or unoccupied. A third charged tRNA enters the A site and the
elongation cycle is replicated (Fig. 8). Following each addition of an amino acid to the
growing polypeptide chain, the ribosome translocates to the next codon. In bacteria,
translocation is mediated by the elongation factor EFG which gets bound to the ribosome
in a complex with GTP. This is then hydrolyzed to provide energy for translocation.
Binding of EFG and EF-Tu to the ribosome is mutually exclusive. This ensures that
translocation is completed before the next round of elongation begins.
Fig. 8. Stepwise elongation of the amino acid chain
For animation on individual steps of translation kindly visithttps://youtu.be/KZBljAM6B1s
14
Fig.9. Prokaryotic Elongation factors EFTu
http://www.ebi.ac.uk/
As translocation proceeds, the ribosomes moves along the mRNA away from the initiation site
which is then free to bind a new ribosome. Several ribosomes can bind to a single mRNA during
the process of protein synthesis, forming a structure known as Polysome / Polyribosome (Fig. 10).
Fig. 10. Polysome or Polyribosome
15
Proofreading mechanism of Ribosomes: Ribosomes make use of three mechanisms to ensure
that incorporation of incorrect aminoacyl tRNA is avoided. The rate of error is almost 10-4.

The presence of adjacent A-A residues on 16srRNA at A site of small subunit forms
hydrogen bonding with the minor groove of codon-anticodon pair. This takes place only if
there is correct base pairing between codon and anticodon.

Secondly, the correct pairing also ensures efficient GTPase activity associated with release
of EFTu. In the absence of correct pairing EFTu is not at its proper place and its
associated GTPase activity is hindered.

Thirdly, correctly base paired aminoacyl tRNA remain associated with ribosome and this
further causes rotation of tRNA (about 70o), a process called “accommodation” that
ensures that 3’end of tRNA comes nearer to the site of peptide bond formation. The
process of accommodation puts so much strain on codon-anticodon pairing that only the
correct pair is able to maintain that stress.
4.3 Termination: When a termination codon enters the A site, it marks the end of translation. The
completed polypeptide is now released. There are no tRNAs that can bind to the termination
codons. Instead proteins called release factors enter the A site and causes the release of
completed polypeptide. In E.coli, two release factors RF1 and RF2 perform this function. RF1
identifies UAA, UAG while RF2 recognizes UAA, UGA. Another factor RF3 plays an ancillary
role. The release factor also promotes the transfer of the polypeptide to a water molecule by
peptidyl transferase rather than to another aminoacyl tRNA (Fig. 11). To complete the ribosome
cycle, a class II release factor, a ribosome recycling factor and IF3 (initiation factor) ensures
complete termination of translation followed by dissociation of ribosome into large and small
subunits that are ready to start another cycle.
16
Fig. 11. Termination in Prokaryotic Protein synthesis
Do you know?
The protein synthesis must not only be fast but accurate as well!
The probability “p” of forming a protein that has no error is dependent on “n”, where n stands
for the number of amino acid residues, and “ϵ”, the frequency of insertion of a wrong amino
acid.
Therefore
P= (1-ϵ) n
The permissible error frequency is 10-4 for large sized proteins and must not exceed that!
5. Post Translational Modification
Following translocation, newly synthesized polypeptides may undergo further modifications to
become functional protein. Modifications may include methylation, phosphorylation, acetylation,
hydroxylation as well as addition of larger molecular structures such as lipids and oligo
saccharides to the newly synthesized polypeptide. Cleavage of polypeptides is also common
which leads to removal of certain internal sequences or removal of amino terminal signal
17
peptides. Cleavage of proteins is also sometimes associated with activation of inactive precursor
proteins.
6. Inhibitors of Protein synthesis
Antibiotics are generally used to study protein synthesis as these works at precise steps during
protein synthesis.
Inhibitor
Puromycin
Mode of action
Analogue of AA-tRNA that can bind at A site and on which the
polypeptide chain formed can get bound, forming polypeptide-puromycin
chain, which is released.
Fusidic acid
block translocation induced by EFG factors
Streptomycin
Causes misreading of genetic message, causing errors in protein, hence
killing the bacteria.
Tetracyclin
inhibits AA-tRNA binding
Sparsomycin
inhibits peptidyl transferase
Chloramphenicol
inhibits protein synthesis in bacteria
Many antibiotics actually inhibit bacterial ribosomes but not eukaryotic ribosomes hence used in
medical treatment.
Antibiotics targeting small ribosomal unit (30S) of the bacteriaA) Aminoglycosides- Apramycin, Paromomycin, Tobramycin,Streptomycin etc.
B) Tetracylines
A
Antibiotics targeting large ribosomal unit (50S) of the bacteriaA) Macrolides- Azithromycin, Erythromycin, Carbomycin etc.
B) Streptogramins- Quinupristin etc
C) Lincosamides-Clindamycin
http://www.lehigh.edu/~inbios21/PDF/Fall2009/Ware_10212009.pdf
18
SummaryTranslation in Prokaryotes is a process that involves decoding the information of mRNA into a
chain of amino acids that finally forms the protein. Four principal components are involved in the
process of protein synthesis. They are: mRNA, tRNA, aminoacyl tRNA synthetase and the
ribosomes. The entire process can be categorized into three major steps-Initiation, Elongation and
Termination. Initiation results in formation of initiation complex wherein small unit of ribosome
is bound to mRNA at the start site and the initiator tRNA is bound to the first or initiator codon,
bound to ribosome. Elongation leads to joining of amino acids to form a polypeptide based on the
information given by the mRNA molecule. The process of elongation comes to an end once the
termination codon is reached on mRNA. This marks the end of elongation and beginning of
Termination that leads to release of ready-made protein from the ribosome. This also marks the
end of ribosome cycle. Newly synthesized protein may undergo post translational modifications
to be fully functional. Certain accessory factors like IF1, IF2 and IF3 in Initiation; EFTu, EFTs
and EFG in Elongation and RF1, RF2 and RF3 play important role during this process. The
process of translation ensures the consistency of mRNA, as the ones that are incomplete (e.g.
devoid of stop codons) may produce truncated proteins that are degraded by cellular proteases.
Interesting facts about Proteins



Low –Sodium Parmesan Cheese is loaded with proteins- about 41.6 g per 100g serving,
making it the most protein-rich cheese of all!
Cataract, the eye disease is due to denaturation of lens’ proteins!
Proteins found in eggs are the best quality proteins found in nature!
Consuming too much protein can be dangerous to the body as it can have adverse
affect on kidney and liver that are involved in its metabolism!
19
Quiz-1: Multiple Choice Questions1. The type of RNA that serves as the Adaptor molecule during prokaryotic translation is –
a)
b)
c)
d)
mRNA
tRNA
rRNA
double stranded RNA
2. During prokaryotic translation, the ribosomal binding site on mRNA is calleda)
b)
c)
d)
Shine-Dalgarno sequence
TATA box
Pribnow box
Hogness sequence
3. Polyribosomes area)
b)
c)
d)
Aggregation of lysosomes in the cell
Aggregation of ribosomes on mRNA
Aggregation of endosomes in the cytoplasm
None of these
4. During prokaryotic translation, peptide bond between consecutive amino acids on the
growing polypeptide chain is formed by the enzymea)
b)
c)
d)
Peptidyl transferase
DNA Polymerase
RNA Polymerase
DNA helicase
5. Initiation complex in prokaryotes is composed ofa)
b)
c)
d)
mRNA, the small ribosomal subunit and tRNAfmet
rRNA, the small ribosomal subunit and tRNAfmet
mRNA, the large ribosomal subunit and tRNAfmet
none of the above
6. Translocation induced by EFG factors is blocked bya)
b)
c)
d)
Tetracycline
Puromycin
Fusidic acid
Erythromycin
7. Prokaryotic rRNA includes20
a)
b)
c)
d)
16S rRNA, 23S rRNA and 5S rRNA
16S rRNA, 23S rRNA and 5.8S rRNA
18S rRNA, 23S rRNA and 5S rRNA
None of the above
8. The anticodon of tRNA binds to
a)
b)
c)
d)
Codons of tRNA
Nucleotide bases of rRNA
Nucleotide bases of mRNA
Amino acid
9. Elongation of polypeptide requires all excepta)
b)
c)
d)
mRNA
formyl met tRNA
EFTu, EFTs and EFG
GTP and peptidyl transferase
10. Which antibiotic inhibits AA-tRNA binding
a)
b)
c)
d)
Tetracycline
Puromycin
Sparsomycin
Neomycin
Quiz 2: State True or False1. E.coli release factor RF1 recognizes UGA
FALSE
2. EFTu, EFTs are involved in elongation during prokaryotic protein synthesis.
TRUE
3. Peptidyl transferase forms the peptide bond between successive amino acids in the
growing polypeptide chain.
TRUE
4. Aminoacyl synthetase has two sites, one to recognize right amino acid and the other to
recognize right tRNA.
TRUE
5. E.coli ribosomes has 24 proteins in smaller subunit
FALSE
Quiz 3: Long Answer questions1. Give a brief account of the role of different initiation factors involved in the initiation of
protein synthesis in Prokaryotes.
2. In Prokaryotic protein synthesis, how does the formation of peptide bond and translocation
of peptidyl tRNA takes place?
21
3. Briefly describe the clover leaf structure of tRNA.
4. Describe the process of translation of mRNA into a polypeptide in Prokaryotes.
5. Write short notes on- a) Initiation Complex, b) Elongation Factors c) Peptidyl transferase
Glossary
1. Amino acid-Organic compounds (20 different types) containing amine group and
carboxylic acid group and combine to form proteins.
2. Aminoacyl-tRNA synthetase-enzyme that is involved in attachment of right amino acid
to its tRNA
3. Initiation Signal- AUG codon on mRNA that directs incorporation of N-formyl
methionine at the beginning of new protein chain.
4. Prokaryotes-Organisms devoid of true nucleus.
5. Translation- Process that involves synthesis of protein from amino acids as per the
information encoded in mRNA
Further Readings:
1. Crick, Francis: From DNA to protein On degenerate templates and the adapter hypothesis:
a note for the RNA Tie Club, 1955.
2. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, and Walter P (2008) Molecular
Biology of the Cell, (5th ed.) Garland Science, New York.
3. Turner PC, McLennan AG, Bates AD, and White MRH (2001). BIOS Instant notes in
Molecular Biology (2nded.)Bios Scientific Publishers Ltd. Oxford, UK
4. Watson, J D, Baker T A, Bell, S P, Gann, A, Levine, M, and Losick, R, (2008) Molecular
Biology of the Gene (6th edition.). Cold Spring Harbour Lab. Press, Pearson Pub.
5. Becker, W M, Kleinsmith, L J, Hardin J and Bertoni, G P (2009) The World of the Cell.
7th edition. Pearson Benjamin Cummings Publishing, San Francisco.
6. De Robertis, EDP and De Robertis, EMF (2006) Cell and Molecular Biology. 8th edition.
Lippincott Williams and Wilkins, Philadelphia.
7. WEB LINKSWikipedia, the free encyclopedia-www.wikipedia.org
https://en.wikipedia.org/wiki/Prokaryotic_translation
https://en.wikipedia.org/wiki/Transcription_preinitiation_complex
https://en.wikipedia.org/wiki/Elongation_factor
http://www.lehigh.edu/~inbios21/PDF/Fall2009/Ware_10212009.pdf
22