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Biosynthesis of proteins on ribosomes

Biosynthesis of proteins on ribosomes. GENETIC CODE - sequence of mononucleotides in mRNA that specifies the sequence of amino acids in peptide chain. CODON – mRNA triplet base sequence responsible for 1 amino acid. PROPERTIES OF GENETIC CODE.

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Biosynthesis of proteins on ribosomes

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  1. Biosynthesis of proteins on ribosomes

  2. GENETIC CODE - sequence of mononucleotides in mRNA that specifies the sequence of amino acids in peptide chain CODON – mRNA triplet base sequence responsible for 1 amino acid

  3. PROPERTIES OF GENETIC CODE • Unambiguous. In any organism each codon corresponds to only one amino acid. • Code is degenerate. There are multiple codons for most amino acids. • 3. Universal. Codons are the same for all organism. • 4. Without punctuation. There are no punctuations between trinucleotides. • 5. Nonoverlapping. Codons do not overlap each other.

  4. ANTICODON – triplet in tRNA that can complementary bind to codon of mRNA. Such base pairing between codon and anticodon is responsible for the translation of genetic information from mRNA to protein. Structure of tRNAs

  5. STAGES OF TRANSLATION 1. Recognition 2. Initiation 3. Elongation 4. Termination

  6. RECOGNITION Aminoacyladenilate Aminoacyl-tRNA-synthetase Aminoacyladenilate + tRNA  aminoacyl-tRNA + AMP

  7. Activation of amino acids Each amino acid has a specific tRNA There is specific aminoacyl-tRNA-synthetase for each AA

  8. The structure of tRNA

  9. Initiation of Translation • The translation complex is assembled at the beginning of the mRNA coding sequence • Complex consists of: -Ribosomal subunits -mRNA template to be translated -Initiator tRNA molecule -Protein initiation factors

  10. Initiator tRNA • First codon translated is usually AUG • Theinitiator tRNA recognizes initiation codons • -Bacteria: N-formylmethionyl-tRNA • -Eukaryotes: methionyl-tRNA

  11. Initiation of protein bio-synthesis Methionyl-тRNAbinds toP-center

  12. Sites for tRNA binding in ribosomes There are two centers: peptidyl (P) andaminoacyl (А)

  13. Elongation 1) Positioning of the next aminoacyl-tRNA in the A site 2) Formation of the peptide bound (enzyme – peptidyl transferase) between methionine and AA in A-centre.The residue of methionine is transferred on the amino group of another AA 3) Translocation– shift of ribosome by one codon. Methionyl-tRNAis released from P-centre. Dipeptidyl-tRNA moves from A-centre to P-centre.

  14. Termination of Translation • Ribosome comes to terminal codon UGA, UAGor UAA • No tRNA molecules recognize these codons and protein synthesis stalls • Protein termination factors F-1, RF-2, RF-3split off synthesized polypeptide from the last tRNA • Ribosomal complex dissociates

  15. Termina-tion of Trans-lation

  16. POSTTRANSLATIONAL MODIFICATION • Preparing of proteins for different functions • Direction of proteins to different locations (targeting) • Removing of methionine (formylmethionine) • Formation of disulfide and other bonds (secondary, tertiary structures) • 3. Proteolyticcleavage • 4. Modification of amino acid residues: • - Hydroxylation • - Glycosilation • - Phosphorilation • 5. Joining of prosthetic groups or cofactors • 6. Formation of the quaternary structure

  17. Regulation of the Protein Biosynthesis The operon model (by Jacob and Monod)

  18. Inhibitors of Transcription

  19. Antibiotics inhibiting protein synthesis

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