This pdf encodes a variety of information regarding Molecular biology and its basic concepts like Translation and Protein synthesis. Various factorial details are provided by proper diagrams. This will help students of B.Sc. especially.

1. Translation In Prokaryotes
Assignment-2
10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 1
Prepared By Apoorva B. Vaghela
Enrollment No. 17BMB054
Department Microbiology Department (GIA)
Semester 6th
Semester (Third Year)
Subject Molecular Biology
College Shree M. & N. Virani Science College (Autonomous)

2. What is Translation?
• Translation is the process that Converts an mRNA sequence into a string of
amino acids that form a Protein.
• It is carried out in both, Eukaryotic as well as Prokaryotic Organisms.
• This fundamental process is responsible for Creating the Proteins that make
up most cells.
• It also marks the Final Step in the journey from DNA sequence to a
functional protein; the last piece of the “Central Dogma” to molecular
biology.
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3. The genetic code
• During translation, a cell “reads” the information in a messenger RNA
(mRNA) and uses it to build a protein.
• An mRNA doesn’t always encode—provide instructions for—a whole
protein. Instead, what we can say is that it always encodes a polypeptide, or
chain of amino acids.
• In an mRNA, the instructions for building a polypeptide are RNA
nucleotides (As, Us, Cs, and Gs) read in groups of three.
• These groups of three are called codons.
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4. • There are 61 codons for amino acids, and each of them is "read" to specify a
certain amino acid out of the 20 commonly found in proteins.
• One codon, AUG, specifies the amino acid methionine and also acts as a start
codon to signal the start of protein construction.
• There are three more codons that do not specify amino acids. These stop
codons, UAA, UAG, and UGA, tell the cell when a polypeptide is complete.
• All together, this collection of codon-amino acid relationships is called
the genetic code, because it lets cells “decode” an mRNA into a chain of
amino acids.
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5. How Codons Are Decided?
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• The Nucleotide sequence is divided in
to triplets.
• These triplets are commonly
combines as per this table to
understand the mechanism off the
translation.
• Based on the combination of these
nucleotide sequence, the respective
amino acids are decided.

6. Factors Involved In Translation
• Translation in a multi-step process, performing various activities at
different stages.
• The process requires,
1. t-RNA
2. m-RNA
3. Ribosome
4. Amino acids
5. Translational Factors
6. Various Enzymes
7. Sources of Energy
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7. t-RNA
• Transfer RNAs, or tRNAs, are molecular "bridges" that connect mRNA
codons to the amino acids they encode.
• One end of each tRNA has a sequence of three nucleotides called
an anticodon, which can bind to specific mRNA codons.
• The other end of the tRNA carries the amino acid specified by the codons.
• There are many different types of tRNAs.
• Each type reads one or a few codons and brings the right amino acid
matching those codons.
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8. m-RNA
• m-RNA strand is synthesized by the process of transcription.
• It contains nucleotides arranged in a way that is complementary to
template DNA strand.
• It contains a start codon, Open reading Frames and a Stop codon.
• To prevent it from being operated by various enzymatic activities, the 3’ end
is adenylated.
• m-RNA strand is commonly operated simultaneously with the transcription
and translation process.
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9. Ribosomes
• Ribosomes are the structures where polypeptides (proteins) are built.
• They are made up of protein and RNA (ribosomal RNA, or rRNA).
• Ribosome also acts as an enzyme, catalyzing the chemical reaction that links
amino acids together to make a chain.
• Sometimes many ribosome simultaneously process on a single m-RNA
strand to produce proteins, these structure is called “POLYSOMES”.
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10. Various Sites of
Ribosome
• Each ribosome has two subunits, a
large one and a small one, which
come together around an mRNA.
• The ribosome provides a set of
handy slots where tRNAs can find
their matching codons on the mRNA
template and deliver their amino
acids.
• These slots are called the A, P, and E
sites.
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11. Structure Of
Ribosome
• Large subunit: (Peptidyl Transferase
Center)
1. Comprises of 50s with the Molecular
Weight of 1,60,000 Daltons.
2. Possesses 34 proteins, and 2 different
rRNA sequences.
• Small subunit: (Decoding Center)
1. Comprises of 30s having the Molecular
Weight of 9,00,000 Daltons.
2. Possesses 21 proteins and 1540
nucleotide long 16s rRNA Sequence.
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12. General Mechanism of Translation
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13. Translational Factors
• Various factors plays an important role in whole translation process.
• These factors are divided in to groups as per the stages of the process.
• Initiation factors (IF) are found during Initiation stage.
• Elongation factors (EF) are found during Elongation stage.
• Release factors (RF) are found during Termination stage.
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14. t-RNA Charging
• It is an important process which helps the translation process to begin.
• In this process the first t-RNA molecule having Methionine is charged with
the Methyl group.
• As the methyl group is associated with t-RNA, now it is considered as formyl
methionine t-RNA or Initiator t-RNA.
• Then it goes to the P-Site of ribosome and gets acted upon by deformylase
enzyme.
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15. Process Of Translation
Termination
Elongation
Initiation
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16. Initiation
• Initiation begins with the small subunit of the Ribosome, known as 30S Subunit.
• This process requires a special tRNA known as the initiator tRNA , which base-pairs with the start codon
usually AUG or GUG.
• AUG and GUG have a different meaning when they occur within an ORF, where they are read by tRNAs for
methionine (tRNAMet) and valine(tRNAVAL), respectively
• With the formation of 30S Initiation Complex, initiation process begins.
• Firstly 30S Subunit will pair with the m-RNA.
• As they binds, Initiation Factors (IF) come across and then binds with the 30S Subunit.
• Initiation Factors are of 3 types mainly: IF1, IF2, IF3.
• IF3 Binds with the E Site of the 30S Subunit and block it.
• IF1 and IF2 will come and bind to the A Site.
• IF2 factor has GTPase activity.
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17. • Ribosome itself contains an RNA[16s rRNA] within it & a particular sequence embedded in it is,
considered as “Shine Dalgarno Sequence”[UCCUC].
• When m-RNA will have Complementary Sequence [AGGAG] with ‘Shine Dalgarno Sequence’, it signals that
it is the start site facing the P-site.
• Then as only P-site is available free, 1rst t-RNA [formylated methionine] will come and attach with P-site
of ribosome.
• Upon binding of 1rst t-RNA correctly with P-site, IF3 unblocks the E-site and releases.
• This assembly is considered as 30s Initiation Complex.
• Now large 50s Subunit comes, having E,P,A sites as well as Translation Factors binding sites.
• Upon binding of large subunit, GTP is hydrolysed and due to it IF2 & IF1 will be released.
• This assembly is considered as 70s Initiation Complex.
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Initiation

18. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 18
Diagrammatic representation of Initiation

19. Elongation
• Now after the formation of 70s Initiation Complex, the ribosome will now slide one
codon to 3’ end of the m-RNA.
• This process also requires several factors like;
1. EF-TU [GTPase activity]
2. EF-G [GTPase Activity]
3. EF-TS
• Now the EF-TU along with GTP will attach to the next t-RNA and bind it to the A-Site, if
the binding is correct then by GTPase activity, EF-TU will be released with GDP.
• ET-TS have ability to recycle the GTP to GDP and it will provide GTP to the releasing EF-
TU and make them able to again bind with the new t-RNA.
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20. • Now the former amino acid residue will bind to new amino acid by formation of peptide
bond.
• Transpeptidation reaction takes place in the large subunit of the Ribosome by an
enzyme called “Peptidyl Transferase”.
• This enzyme helps the amino acid binding by transpeptidation.
• EF-G will now bind with the large subunit and as it’s GTP will hydrolyse, the whole
assembly will slide 1 codon to 3’ end of the m-RNA and GDP along with EF-G will be
released and uncharged t-RNA will be released from E-Site.
• So now the peptide chain will automatically move towards P-Site and again A-site will be
free for new t-RNA.
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Elongation

21. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 21
Diagrammatic representation of Elongation

22. • In Elongation, when stop codon will appear on m-RNA, instead of a t-RNA there, a
new molecule called RF (Release Factor) will be put.
• RF-1 (t-RNA mimicking protein) will come and bind with A-Site.
• RF-1 has 2 domains in its structure, one will pair with stop codon and another
domain having exonuclease activity, will break the bond between last t-RNA and
polypeptide chain from P-Site.
• As a result, whole protein structure comes out from the ribosome.
• Then RF-2 along with GDP comes and will break the bond between RF-1 and stop
codon and this energy will convert GDP into GTP and as a result RF-1 is released.
• Now both E and P sites will be occupied by uncharged t-RNA and A-Site will be
empty.
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Termination

23. • Then RRF (Ribosome Release Factor) along with EF-G comes on A-Site and
EF-G will convert GTP into GDP.
• This process will drive the ribosome downstream to m-RNA and as a result
E-Site’s uncharged t-RNA will be released.
• RRF provides some signals and due to it the IF-3 comes and binds with the
E-Site.
• IF-3 prevents attachment of both subunits, so upon it’s binding m-RNA and
both subunits will be separated.
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Termination

24. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 24
Diagrammatic representation of Termination

25. References
• https://www.sparknotes.com/biology/molecular/translation/summary/
• https://www.khanacademy.org/science/biology/gene-expression-central-
dogma/translation-polypeptides/a/translation-overview
• https://www.youtube.com/channel/UCEPMCywJ6FPZpQ_aPEZt5JA
• [WATSON] MOLECULAR BIOLOGY OF THE GENE
• BECKER [Jeff_Hardin,_Gregory_Paul_Bertoni,_Lewis_J._Klein]
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26. Thank You
What's been gratifying is to live long enough to see
molecular biology and evolutionary biology growing
toward each other and uniting in research efforts.
E. O. Wilson
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