PROTEIN SYNTHESIS-Arun M. Chilke

PROTEIN SYNTHESIS: 

PROTEIN SYNTHESIS Dr. Arun M. Chilke Head, Department of Zoology Division of Toxicology and Biomonitoring Shree Shivaji Arts, Commerce and Science College, Rajura-442905 (India) E-mail: achilke.2011@rediffmail.com www.sscollegerajura.org

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Central Dogma Replication DNA PROTEIN RNA Transcription Reverse transcription Translation DNA replicate or duplicate to produce exact copy of itself in the presence of DNA dependent DNA polymerase ( Replicase ). However, transcribe in the presence of DNA dependent RNA polymerase to RNA and RNA translate into Polypeptide chain Of amino acids (Protein) and exhibit the one way information flow. In some viruses RNA in the presence of RNA dependent DNA polymerase ( Reverse Transcriptase) produces the DNA .

Central Dogma makes you Understand how the genetic information flow: 

Central Dogma makes you Understand how the genetic information flow You are aquainted with the DNA, that contains several distinct or repetitive gene sequences. Characteristic of the DNA is: It has its own property, that, it can prepare exact copies of itself and this process is known as replication . Replicated product is exactly the replica of parent DNA strand, and hence, the resultant daughter DNAs are same to same. What we called xerox copy or dicto. Another property of DNA is that, it is capable of undergoing the transcription by which they produce complementary copy, we call m-RNA. This process is catalyse by Transcriptase or DNA-dependent RNA-Polymerase. Thus, m-RNA synthesized on the DNA-template is capable for translating the genetic message brought from DNA to sequence of amino acids in the polypeptide chain or protein, called translation . You would have understood, how the genetic information function from DNA to Protein mediated through m-RNA. This is the central dogma of protein synthesis.

Mechanism of Protein synthesis: 

Mechanism of Protein synthesis There are two important phenomenon takes place during protein synthesis. They are: Transcription Translation Reverse transcription is also one of the important process by which RNA can synthesis DNA, and this process is catalyse by RNA-dependent-DNA-Polymerase ( Reverse Transcriptase ). Some viruses carry RNA as genetic material and this acellular organism when infect the host cell they also carry the above said enzyme. By utilising the whole synthetic machinery, this virus synthesizes the DNA from its own RNA and thence several copies of RNA and also the required proteins and consequently the viruses.

TRANSCRIPTION: 

TRANSCRIPTION Transcription is the first process of protein synthesis. This activity requires some components of transcription machinery, they are: 1. Template DNA (Deoxyribose polynucleotide). 2. Activator components of Ribonucleoside triphosphate , i.e., ATP (Adenine ribose triphosphate):- A-p-p-p. GTP- (Guanine ribose triphosphate):- G-p-p-p. CTP (Cytosine ribose triphosphate):- C-p-p-p and UTP (Uracil ribose triphosphate):- U-p-p-p. 3. Divalent metal ions: Mg++ and Mn++ 4. RNA-Polymerase (Transcriptase)

DNA-Template: 

DNA-Template ds-DNA ss-DNA Template DNA-strand m-RNA 1. Asymmetrical DNA transcription 2. Symmetrical DNA transcription Both the strands when synthesize the m-RNA is called symmetrical transcription ds-DNA ss-DNA m-RNA m-RNA

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Activator components of Ribonucleoside triphosphate ATP (Adenine ribose triphosphate) CH2 H Guanine Ribose Triphosphate GTP (Guanine ribose triphosphate) CH2 H Adenine Ribose Triphosphate

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CH2 H Cytosine Ribose Triphosphate CH2 H Guanine Ribose Triphosphate

RNA Polymerase: 

RNA Polymerase RNA Polymerase is a spectacular enzyme, functioning in: Recognition of the promoter region Melting of DNA (Helicase + opisomerase) RNA Priming (Primase) RNA Polymerization Recognition of terminator sequence β’ β ω σ β’ β ω σ β’ β ω σ β’ β ω σ

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Initiation of Transcription Promoter region of DNA (Gene ) Recognition site Binding site Initiation site 5 TATpuATG 3 7-base pairs β’ β ω σ β’ β ω σ Diffusion of RNA polymerase from Recognition to binding site RNA polymerase finally binds to Initiation site to start the transcription Sigma factor β’ β ω σ RNA polymerase

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ds-DNA Core enzyme Sigma factor Activated RNA-polymerase Template DNA stand Initiation of RNA synthesis on initiation site asymmetrical Transcription Symmetrical Transcription Protein d e a b c RNA Protein a b c RNA Transcription begins on both DNA strands Transcription begins on only one DNA strands

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m-RNA m-RNA Unwinding of DNA Dissociation of Sigma factor ρ m-RNA elongation 5 ’ 3 ’ Synthesis of RNA in the direction 5’ to 3’ on sense strand of DNA Elongation of RNA transcript

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Termination of RNA synthesis Transcription terminates by two methods- 1. By Poly-A sequence interaction with RNA polymerase and 2. By Rho-factor interaction. 1. Poly-A sequence interaction with RNA polymerase m-RNA Dissociation of both RNA and RNA polymerase m-RNA A A A A A A A U U U U U U U m-RNA transcript with poly U-tail

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2. Termination of Transcription by Rho-factor interaction. m-RNA Dissociation of both RNA and RNA polymerase Rho-factor m-RNA

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TRANSLATION

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Activation of Amino acids Transfer of activated amino acids to t-RNA Initiation of Protein Synthesis Chain elongation Chain termination

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Activation of Amino acids E Amino acid ATP Amino acyl t-RNA synthetase + E + Aminoacyl Adnylate Pyrophosphate + Pyrophosphate AMP

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Anticodon E + E + + AMP 2. Transfer of Activated Amino acids to t-RNA

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IF-1 IF-2 IF-3 m-RNA 5’ 3’ AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA 30-S Small ribosome subunit m-RNA 5’ 3’ IF-3 AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA 4. Initiation of Protein Synthesis

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Anticodon UAC m-RNA 5’ 3’ AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA IF-3 IF-1 IF-2 50-S Anticodon t-RNA m-RNA 5’ 3’ IF-3 UAC IF-1 IF-2 N-formylmethionine CGG AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA

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CGG UAC m-RNA 5’ 3’ IF-3 IF-1 IF-2 AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA 5’ 3’ UAC IF-3 IF-1 IF-2 CGG A P E AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA 5. Elongation of polypeptide chain

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AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA CGG UGA AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA CGG UGA

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CCC UUG AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA TF-1 AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA UGG UGA CGG 6. Termination protein synthesis

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UUG AUGGCCACUACCACGCGCACCCAGUCAUUCAAGGCAACUUUUCACCAACGGGACGUUA TF-1

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