Nucleic acids and proteins synthesis

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DNA RNA protein synthesis

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  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.3 Overview: the roles of transcription and translation in the flow of genetic information.
  • Figure 17.9 Transcription elongation.
  • Figure 17.12 The roles of snRNPs and spliceosomes in pre-mRNA splicing.
  • Figure 17.12 The roles of snRNPs and spliceosomes in pre-mRNA splicing.
  • Figure 17.12 The roles of snRNPs and spliceosomes in pre-mRNA splicing.
  • Figure 17.16 An aminoacyl-tRNA synthetase joining a specific amino acid to a tRNA.
  • Figure 17.16 An aminoacyl-tRNA synthetase joining a specific amino acid to a tRNA.
  • Figure 17.16 An aminoacyl-tRNA synthetase joining a specific amino acid to a tRNA.
  • Figure 17.16 An aminoacyl-tRNA synthetase joining a specific amino acid to a tRNA.
  • Figure 17.17 The anatomy of a functioning ribosome.
  • Figure 17.17 The anatomy of a functioning ribosome.
  • Figure 17.17 The anatomy of a functioning ribosome.
  • Figure 17.17 The anatomy of a functioning ribosome.
  • Figure 17.19 The elongation cycle of translation.
  • Figure 17.19 The elongation cycle of translation.
  • Figure 17.19 The elongation cycle of translation.
  • Figure 17.19 The elongation cycle of translation.
  • Nucleic acids and proteins synthesis

    1. 1. BIOSYNTHESIS OF NUCLEIC ACIDS AND PROTEINS
    2. 2. The flow of genetic information in a typical cell DNA ↓ RNA ↓ protein
    3. 3. Primary structure of nucleic acids
    4. 4. Two-stranded structure of DNA
    5. 5. Watson JamesCrick Francis The double helix of DNA was discovered in 1953 by Crick F. and Watson J. Nobel prize in 1962.
    6. 6. When replication takes place?
    7. 7. What are the principles of replication? • Based on template; • Complementary; • Antiparallel; • Two directions; • Semi-conservative; • Very complex.
    8. 8. Components required for replications • DNA molecule - template • Origin of replication – point ORI • Enzymes • Nucleotides (dNTP and NTP) • SSB proteins
    9. 9. Main enzymes required for replication • DNA-polymerase (I, II, III – in prokaryotes, , ,ᵅ ᵞ ᵋ – in eukaryotes) • Primase • DNA-helicases • Topoisomerase • DNA-ligase • Telomerase
    10. 10. Topoisomerase Protein complexes of the replication fork DNA replication
    11. 11. Reiji Okazaki provided experimental evidence for discontinuous DNA synthesis
    12. 12. Details of lagging strand synthesis
    13. 13. DNA mRNA Ribosome Polypeptide TRANSCRIPTION TRANSLATION TRANSCRIPTION TRANSLATION Polypeptide Ribosome DNA mRNA Pre-mRNA RNA PROCESSING (a) Bacterial cell (b) Eukaryotic cell Nuclear envelope
    14. 14. TRANSCRIPTION DNA mRNA (a) Bacterial cell
    15. 15. TRANSCRIPTION DNA mRNA (a) Bacterial cell TRANSLATION Ribosome Polypeptide
    16. 16. Nuclear envelope DNA Pre-mRNA (b) Eukaryotic cell TRANSCRIPTION
    17. 17. RNA PROCESSING Nuclear envelope DNA Pre-mRNA (b) Eukaryotic cell mRNA TRANSCRIPTION
    18. 18. RNA PROCESSING Nuclear envelope DNA Pre-mRNA (b) Eukaryotic cell mRNA TRANSCRIPTION TRANSLATION Ribosome Polypeptide
    19. 19. Nontemplate strand of DNA RNA nucleotides RNA polymerase Template strand of DNA 3′ 3′5′ 5′ 5′ 3′ Newly made RNA Direction of transcription A A A A A A A T T T T TTT G G G C C C C C G C CC A A A U U U end
    20. 20. Initiation and elongation steps of transcription
    21. 21. Biochemistry For Medics- Lecture Notes 26 Post TranscriptionalPost Transcriptional modifications ofmodifications of pre m- RNApre m- RNA • In prokaryotic organisms, the primary transcripts of mRNA-encoding genes begin to serve as translation templates even before their transcription has been completed. • In all eukaryotes the primary transcripts of mRNA-encoding genes undergo extensive processing before they are converted to mature functional forms
    22. 22. Post Transcriptional modifications ofPost Transcriptional modifications of pre m- RNApre m- RNA a) 5' Capping • Mammalian mRNA molecules contain a 7- methylguanosine cap structure at their 5' terminal. • The cap structure is added to the 5' end of the newly transcribed mRNA precursor in the nucleus prior to transport of the mRNA molecule to the cytoplasm. • The 5' cap of the RNA transcript is required both for efficient translation initiation and protection of the 5' end of mRNA from attack by 5-'3' exonucleases. • Eukaryotic m RNAs lacking the cap are not efficiently translated. 28
    23. 23. Post Transcriptional modifications ofPost Transcriptional modifications of pre m- RNApre m- RNA •The addition of the Guanosine triphosphate (part of the cap is catalyzed by the nuclear enzyme guanylyl transferase. •Methylation of the terminal guanine occurs in the cytoplasm. and is catalyzed by guanine-7- methyl transferase. •S-Adenosyl methionine is the methyl group donor. •Additional methylation steps may occur. The secondary methylations of mRNA molecules, those on the 2'-hydroxy and the •N6 of adenylyl residues, occur after the mRNA molecule has appeared in the cytoplasm 29
    24. 24. Post Transcriptional modifications ofPost Transcriptional modifications of pre m- RNApre m- RNA b) Addition of poly A tail • Poly(A) tails are added to the 3' end of mRNA molecules in a posttranscriptional processing step. • The mRNA is first cleaved about 20 nucleotides downstream from an AAUAA recognition sequence • Another enzyme, poly(A) polymerase, adds a poly(A) tail which is subsequently extended to as many as 200 A residues. • The poly(A) tail appears to protect the 3' end of mRNA from 3' 5' exonuclease attack. • Histone and interferon's mRNAs lack poly A tail. • After the m-RNA enters the cytosol, the poly A tail is gradually shortened. 30
    25. 25. Post Transcriptional modifications ofPost Transcriptional modifications of Pre m RNAPre m RNA Removal of introns (Splicing) • Introns or intervening sequences are the RNA sequences which do not code for the proteins. • These introns are removed from the primary transcript in the nucleus, exons (coding sequences) are ligated to form the mRNA molecule, and the mRNA molecule is transported to the cytoplasm. • The steps of splicing are as follows- 32
    26. 26. Post Transcriptional modifications ofPost Transcriptional modifications of Pre m RNAPre m RNA • Introns are removed from the primary transcript in the nucleus, exons (coding sequences) are ligated to form the mRNA molecule 33
    27. 27. Figure 17.12-1 RNA transcript (pre-mRNA) 5′ Exon 1 Protein snRNA snRNPs Intron Exon 2 Other proteins
    28. 28. Figure 17.12-2 RNA transcript (pre-mRNA) 5′ Exon 1 Protein snRNA snRNPs Intron Exon 2 Other proteins Spliceosome 5′
    29. 29. Figure 17.12-3 RNA transcript (pre-mRNA) 5′ Exon 1 Protein snRNA snRNPs Intron Exon 2 Other proteins Spliceosome 5′ Spliceosome components Cut-out intronmRNA 5′ Exon 1 Exon 2
    30. 30. Nirenberg Marshall decoded the genetic code. Nobel prize, 1968
    31. 31. 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
    32. 32. PROPERTIES OF GENETIC CODE 1. Degenerate 2. Specific 3. Nonoverlapping 4. Without punctuation 5. Universal
    33. 33. TRANSLATION • 1. Recognition • 2. Initiation • 3. Elongation • 4. Termination
    34. 34. Formation of aminoacyl tRNAs by aminoacyl tRNA synthetase. RECOGNITION
    35. 35. Aminoacyl-tRNA synthetase (enzyme) Amino acid P P P Adenosine ATP Figure 17.16-1
    36. 36. Aminoacyl-tRNA synthetase (enzyme) Amino acid P P P Adenosine ATP P P P P Pi i i Adenosine Figure 17.16-2
    37. 37. Aminoacyl-tRNA synthetase (enzyme) Amino acid P P P Adenosine ATP P P P P Pi i i Adenosine tRNA AdenosineP tRNA AMP Computer model Amino acid Aminoacyl-tRNA synthetase Figure 17.16-3
    38. 38. Aminoacyl-tRNA synthetase (enzyme) Amino acid P P P Adenosine ATP P P P P Pi i i Adenosine tRNA AdenosineP tRNA AMP Computer model Amino acid Aminoacyl-tRNA synthetase Aminoacyl tRNA (“charged tRNA”) Figure 17.16-4
    39. 39. Components of a 70S prokaryotic ribosome
    40. 40. tRNA molecules Growing polypeptide Exit tunnel E P A Large subunit Small subunit mRNA 5′ 3′ (a) Computer model of functioning ribosome Exit tunnel Amino end A site (Aminoacyl- tRNA binding site) Small subunit Large subunit E P A mRNA E P site (Peptidyl-tRNA binding site) mRNA binding site (b) Schematic model showing binding sites E site (Exit site) (c) Schematic model with mRNA and tRNA 5′ Codons 3′ tRNA Growing polypeptide Next amino acid to be added to polypeptide chain Figure 17.17
    41. 41. Figure 17.17a tRNA molecules Growing polypeptide Exit tunnel E P A Large subunit Small subunit mRNA 5′ 3′ (a) Computer model of functioning ribosome
    42. 42. Figure 17.17b Exit tunnel A site (Aminoacyl- tRNA binding site) Small subunit Large subunit P A P site (Peptidyl-tRNA binding site) mRNA binding site (b) Schematic model showing binding sites E site (Exit site) E
    43. 43. Figure 17.17c Amino end mRNA E (c) Schematic model with mRNA and tRNA 5′ Codons 3′ tRNA Growing polypeptide Next amino acid to be added to polypeptide chain
    44. 44. Initiation of protein biosynthesis in prokaryotes.
    45. 45. Elongation of the Polypeptide Chain • During the elongation stage, amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain • Each addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation • Translation proceeds along the mRNA in a 5′ to 3′ direction
    46. 46. Amino end of polypeptide mRNA 5′ E P site A site 3′
    47. 47. Amino end of polypeptide mRNA 5′ E P site A site 3′ E GTP GDP + P i P A
    48. 48. Amino end of polypeptide mRNA 5′ E P site A site 3′ E GTP GDP + P i P A E P A Elongation 1) Positioning of aminoacyl-tRNA in the A site 2) Formation of the peptide bound (enzyme – peptidyl transferase) 3) Translocation
    49. 49. Amino end of polypeptide mRNA 5′ E A site 3′ E GTP GDP + P i P A E P A GTP GDP + P i P A E Ribosome ready for next aminoacyl tRNA P site
    50. 50. Termination of translation in prokaryotes
    51. 51. POSTTRANSLATIONAL MODIFICATION 1) Preparing of proteins for different functions 2) Direction of proteins to different locations (targeting) 1. Proteolytic cleavage 2. Hydroxylation 3. Glycosilation 4. Phosphorilation 5. Lipophilic modification
    52. 52. The operon model (by Jacob and Monod)
    53. 53. Some inhibitors of transcription
    54. 54. Some antibiotics that act by interfering with protein biosynthesis

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