Molecular Biology

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A presentation on Translation..

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TRANSLATION Group members: Muhammad Musharaf FA10-BSB-002 Ghazanfar Ali Baig FA10-BSB-024 Instructor name: Dr. Saadia Naseem 2 COMSATS University of Science & technology, Islamabad

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Central Dogma 3

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DEFINITION: The process by which Protein is synthesized is called Translation, because the language of nucleic acid bases is translated into language of protein amino acid. The production of functional protein . 4

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CODON A group of three nucleotides that specifies an amino acid is known as codon.  Information for translation is coded in mRNA in the form of codon. 61 different codons specifies amino acids. The remaining three codons signal termination of protein synthesis. Start codon is AUG. Termination UAA, UAG, UGA Codon Wheel  5

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COMPONENTS OF PROTEIN SYNTHESIS mRNA carries the information that directs protein synthesis. Protein synthesis occurs on the surface of Ribosomes tRNA molecules carry amino acid to mRNA on the Ribosome A tRNA molecules attach to a mRNA template by means of its ANTI-Codon. A specific sequence of three basis allocated at bottom of tRNA molecule in the middle loop. tRNA molecules can base pair to more than one codon Aminoacyl -tRNA synthetases catalyze bond formation between tRNA molecule & specific amino acid 6

mRNA carries the information that directs protein synthesis.:

mRNA carries the information that directs protein synthesis. In translation, the nucleotide sequence information of an mRNA is translated into a sequence of amino acid in a protein. Bacteria don’t have a nucleus, bacterial mRNAs, are synthesized and translated in the cytoplasm. Eukaroyotic mRNA are synthesized in the nucleus but are translated into protein in the cytoplasm. 7

Protein synthesis occurs on the surface of Ribosomes:

Ribosomes are complexes of ribosomal RNA. Proteins located in the cytoplasm of eukaryotic and bacterial cells. Ribosomes consists of a small subunit that binds an mRNA molecule. And a large subunit that joins the mRNA/small complex to form a complete ribosome. The large subunit has a so-called P-site. P-site holds the growing polypeptide chain . A-site which binds the next amino acid to added to the growing polypeptide side. Protein synthesis occurs on the surface of Ribosomes 8

tRNA molecules carry amino acid to mRNA on the Ribosome:

tRNA molecules carry amino acid to mRNA on the Ribosome The amino acid used in protein synthesis never directly contact the mRNA template that is attached to the small ribosomal subunit. The amino acids are aligned on the mRNA by means of tRNA molecules. These short single-stranded RNAs fold into L-shaped molecules by H-bonding between complementary base sequences. The middle loop (located at the bottom of the tRNA molecule) is the site of attachment to the mRNA template; The 3 / end of the tRNA (at the top of the molecule) is the attachment site for its amino acid. 9

A tRNA molecules attach to a mRNA template by means of its ANTI-Codon.:

A tRNA molecules attach to a mRNA template by means of its ANTI-Codon. tRNA molecule carrying the amino acid serine base pair to the mRNA codons that specify serine. tRNA carrying the amino acid leucine base pair to codons that specify leucine , & so on. Complementary base pairing between the anti-codon (tRNA) and codon (mRNA) ensures that the correct amino acid is aligned on the mRNA template. The formation of non-Watson-C rick base pair plays an important role in the protein synthesis. 10

tRNA molecules can base pair to more than one codon:

tRNA molecules can base pair to more than one codon 61 of the 64 codons specify amino acids, but many organisms contain less than 61 different tRNA molecules. 46 tRNA molecules with different anti-codons have been identified in yeast. tRNA molecules are unusual in the some tRNA anti-codons can form non- Waston -Crick base pair. The ability of tRNA molecules to form non- Waston -Crick base pair with the third base of the mRNA codon is referred to as Wobble. Wobble Rules ensures that a single tRNA molecule can only base pair to different codons that specify same amino acid. Most codons that specify the same amino acid differ only in the third base. 11

Aminoacyl-tRNA synthetases catalyze bond formation between tRNA molecule & specific amino acid :

Aminoacyl-tRNA synthetases catalyze bond formation between tRNA molecule & specific amino acid Each amino acid has a specific aminoacyl -tRNA synthetase enzyme that catalyzes its attachment to a specific tRNA molecule. The formation of a tRNA amino acid complex is an energy requiring process driven by the hydrolysis of ATP. The bond that is formed between the tRNA and its amino acid is high energy bond. A tRNA molecule carrying an amino acid is said to be Charged. The energy trapped in the bond between the tRNA and its amino acid is later used to drive formation of peptide bond, that will join that amino acid to the growing protein chain. 12

Translation: Building a Protein :

Translation: Building a Protein Steps involved in the building of a protein. Initiation Elongation Termination 13

INITIATION :

INITIATION Ribosomal subunit binds an initiator tRNA & mRNA In eukaryots tRNA carries the amino acid methionie In bacteria derivatve of methionine called N-formal methionine. The initiator tRNA base pairs to the initiator codon AUGon the mRNA The large ribosomal subunit joins to the small subunit to form initiatiion complex In most bacteria mRNAs, the initiator codon is preceded by a special sequence called (RBS) ribosomal binding site or Shine – Dalgarno sequence. An mRNA that give rise to multiple protein is said to be polycistronic 14

Continued……:

Continued…… In eukaryotes there is only one initiator AUG codon per nuclear mRNA & only one type of protein is produced Eukaryotes nuclear mRNA are therefore monocistronic 15

Difference b/w Bacterial and Eukaryotic Protein Synthesis:

Difference b/w Bacterial and Eukaryotic Protein Synthesis Bacteria Eukaryotes 70S ribosomes 80S Ribosomes 1 st amino acid N-formal methionine 1 st amino acid is methionone RBS sequences 5-methylguanocine cap Polycistronic mRNA Monocistronic mRNAs Couple transcription/translation Compartmentalized transcription/ translation mRNA half-life =1-3 min mRNA half-life =30min-10 hrs 16

ELONGATION :

ELONGATION In the initiation complex, the tRNA occupies the P-site of large ribosomal subunit . The codon that specifies the second amino acid lies immediately below the A-site with the help of protein called Elongation factor- TU And the energy released by the hydrolysis of one GTP molecule. N- Formyl -methionine leaves the initiator tRNA in the P- site and forms a peptide bond with the second amino acid in the A-site This process is catalyzed by peptidal transferase . 17

Continued……..:

Continued…….. In the final step the growing peptide chain that is now attached to the tRNA in the A-site is “translocated” to the P-site. 18

TERMINATION…..:

TERMINATION….. Termination of protein synthesis occur of the three stop codons UAA,UGA,UAG Enters the A site of the ribosomes There are no tRNA molecules that recognize the stop codons A protein called a release factor binds to the A site and cause hydrolysis The completed polypeptide is released and the ribosomes separates into its small and large subunits in preparation for the next round of protein synthesis. 19

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Continued…….. 20

PROTEINS ARE SYNTHESIZED FROM THE N- TERMINUS TO THE C- TERMINUS :

PROTEINS ARE SYNTHESIZED FROM THE N- TERMINUS TO THE C- TERMINUS Every amino acid contains an amino ( - NH 2 ) group and a carboxyl( - COOH) group When two amino acids join together to form a peptide bond, The amino group of one amino acid joins to the carboxyl group of the other amino acid . 21

References….. :

References….. Molecular Biology (Genes to Protein) by Burton E. Tropp Biochemistry & Molecular Biology by William H. Elliott & Daphne C. Elliott Introduction to Molecular Biology by Deanna Raineri 22

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