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DNA, RNA, and Protein Synthesis
Importance and Structure of DNA:  Deoxyribo-Nucleic Acid <ul><li>Historical Review: </li></ul><ul><ul><li>1900’s – Morgan’...
Figure 16.2a  The Hershey-Chase experiment: phages
Figure 16.2b  The Hershey-Chase experiment
Phages Infecting a bacterium
Figure 16.1  Transformation of bacteria – Griffith (and later Avery, McCarty and MacLeod)
The Structure of DNA <ul><li>Nucleotide monomers: </li></ul><ul><ul><li>Phosphate </li></ul></ul><ul><ul><li>Pentose Sugar...
Structure of DNA cont’ <ul><li>Polynucleotide chain with linkage via phosphates to next sugar, with nitrogen base away fro...
Beginning of the 1950’s several labs were studying the structure of DNA <ul><li>Maurice Wilkins & Rosalind Franklin </li><...
Figure 16.4  Rosalind Franklin and her X-ray diffraction photo of DNA
Watson and Crick
April 1953 – Classical one page paper in  Nature  by Watson and Crick <ul><li>A double helix – 2 polynucleotide strands </...
Figure 16.5  The double helix
Internal Structure of DNA:  Purine and pyridimine?  REMEMBER X-RAY DATA
Confirms Erwin Chargaff’s Rules  <ul><li># of Adenine  = to # of thymine </li></ul><ul><li># of guanine equal to # of cyto...
Information storage in DNA <ul><li>The 4 nitrogenous bases are the “alphabet” or code for all the traits the organism poss...
Replication/Duplication of DNA <ul><li>Due to complimentary base paring – one strand of DNA determines the sequence of the...
Figure 16.7  A model for DNA replication: the basic concept (Layer 1)
Figure 16.7  A model for DNA replication: the basic concept (Layer 2)
Figure 16.7  A model for DNA replication: the basic concept (Layer 3)
Figure 16.7  A model for DNA replication: the basic concept (Layer 4)
Figure 16.8  Three alternative models of DNA replication
Figure 16.9  The Meselson-Stahl experiment tested three models of DNA replication (Layer 1)
Figure 16.9  The Meselson-Stahl experiment tested three models of DNA replication (Layer 2)
Figure 16.9  The Meselson-Stahl experiment tested three models of DNA replication (Layer 3)
Figure 16.9  The Meselson-Stahl experiment tested three models of DNA replication (Layer 4)
There are a series of enzymes that control DNA replication – enzymes which: <ul><li>Uncoil the original double helix stran...
DNA REPLICATION
Figure 16.10  Origins of replication in eukaryotes
Figure 16.11  Incorporation of a nucleotide into a DNA strand
<ul><li>The carbons of the deoxyribose sugar are numbered </li></ul><ul><li>#3 carbon attached to an -OH group </li></ul><...
Definitions <ul><li>Origins of Replication – where replication of the DNA molecule begins </li></ul><ul><ul><li>Bacteria –...
More Definitions <ul><li>DNA Polymerases – enzymes that catalyze DNA replication </li></ul><ul><li>Leading Strand – Synthe...
Definitions Cont’ <ul><li>Ligase – combines (joins) short fragments  </li></ul><ul><li>Primer – starts replication of DNA ...
DNA REPLICATION -VIDEO
Figure 16.13  Synthesis of leading and lagging strands during DNA replication
Figure 16.14  Priming DNA synthesis with RNA
Figure 16.15  The main proteins of DNA replication and their functions
Figure 16.16  A summary of DNA replication
Figure 16.17  Nucleotide excision repair of DNA damage
A PROBLEM! <ul><li>The end of the leading strand was initiated with an RNA primer </li></ul><ul><ul><li>Normally removed b...
Prokaryotes have circular DNA – no problem at ends (there aren’t ANY! <ul><li>Eukaryotes – have special terminal sequences...
Figure 16.19a  Telomeres and telomerase: Telomeres of mouse chromosomes
Ribonucleic Acid (RNA) <ul><li>Structure of RNA </li></ul><ul><ul><li>Nucleotide monomer </li></ul></ul><ul><ul><ul><li>Ph...
Synthesis of RNA - transcription <ul><li>DNA acts as a template, but only one strand of DNA utilized at a given time </li>...
Figure 17.2  Overview: the roles of transcription and translation in the flow of genetic information (Layer 1)
Figure 17.2  Overview: the roles of transcription and translation in the flow of genetic information (Layer 2)
Figure 17.2  Overview: the roles of transcription and translation in the flow of genetic information (Layer 3)
Figure 17.2  Overview: the roles of transcription and translation in the flow of genetic information (Layer 4)
Figure 17.2  Overview: the roles of transcription and translation in the flow of genetic information (Layer 5)
Figure 17.6  The stages of transcription: initiation, elongation, and termination (Layer 1)
Figure 17.6  The stages of transcription: initiation, elongation, and termination (Layer 2)
Figure 17.6  The stages of transcription: initiation, elongation, and termination (Layer 3)
Figure 17.6  The stages of transcription: initiation, elongation, and termination (Layer 4)
Figure 17.6  The stages of transcription: elongation
Three types of RNA <ul><li>mRNA : messenger RNA </li></ul><ul><ul><li>Transcribed from a specific segment of DNA which rep...
Three types of RNA
Protein Synthesis = Translation <ul><li>Ribosomes = sites of protein synthesis </li></ul><ul><ul><li>30% - 40% protein </l...
Ribosomes bring mRNA together with amino acid bearing tRNA’s <ul><li>Three ribosomal sites </li></ul><ul><ul><li>P Site (p...
Figure 17.15  Translation – the basic concept
Preparation of Eukaryotic mRNA <ul><li>RNA splicing- a cut and paste job to remove nucleotides from transcribed mRNA </li>...
 
Figure 17.17  The initiation of translation
Figure 17.18  The elongation cycle of translation
Protein Synthesis (cont’) Initiation – elongation - termination <ul><li>Starting at one end of the mRNA, the small ribosom...
Figure 17.4  The dictionary of the genetic code
Figure 17.3  The triplet code
tRNA complexes with its amino acid in the cytoplasm using ATP – activated tRNA <ul><li>The activated tRNA-amino acid compl...
The first tRNA and its amino acid now occupy the P site of the large ribosomal subunit <ul><li>Review – at this point the ...
Protein Synthesis (continued) <ul><li>At this point, there are 2 tRNA-amino acid complexes adjacent to each other – Elonga...
Translocation – the ribosome moves the tRNA into the A site, and its attached peptide to the P site, as the previous tRNA ...
Yet More Protein Synthesis <ul><li>The empty tRNA from the P site moves in to the E site and leaves the ribosome  </li></u...
A question? <ul><li>Every time a new codon is exposed in the A site, a specific tRNA-AA complex moves into the site.  What...
The Answer! <ul><li>The original DNA that was transcribed </li></ul><ul><li>This elongation of 1 AA takes about 0.1 s </li...
FINALLY - SUMMARY <ul><li>The take home message: </li></ul><ul><ul><li>At the ribosome, the genetic language of DNA is tra...
Figure 17.17  The initiation of translation
Figure 17.18  The elongation cycle of translation
Figure 17.19  The termination of translation
Figure 17.20  Polyribosomes
Table 17.1  Types of RNA in a Eukaryotic Cell
Figure 17.23  The molecular basis of sickle-cell disease: a point mutation
Figure 17.24  Categories and consequences of point mutations: Base-pair insertion or deletion
Figure 17.24  Categories and consequences of point mutations: Base-pair substitution
Figure 17.25  A summary of transcription and translation in a eukaryotic cell
Figure 18.19  Regulation of a metabolic pathway
Control of Protein Synthesis Regulation of Gene Expression <ul><li>Every cell has the same numbers and types of chromosome...
Regions of the Operon (DNA) <ul><li>Promoter region : promotes transcription by binding with RNA polymerase </li></ul><ul>...
Figure 18.20a  The  trp  operon: REPRESSIBLE
Figure 18.21a  The  lac  operon: INDUCIBLE
Figure 19.7  Opportunities for the control of gene expression in eukaryotic cells
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Transcript of "5 DNA RNA Protein Synthesis"

  1. 1. DNA, RNA, and Protein Synthesis
  2. 2. Importance and Structure of DNA: Deoxyribo-Nucleic Acid <ul><li>Historical Review: </li></ul><ul><ul><li>1900’s – Morgan’s studies with fruit flies showed that genes were located on chromosomes and chromosomes consisted of protein and DNA </li></ul></ul><ul><ul><li>1952- Hershey-Chase demonstrated that DNA (not protein) was the genetic material of a viral phage </li></ul></ul>
  3. 3. Figure 16.2a The Hershey-Chase experiment: phages
  4. 4. Figure 16.2b The Hershey-Chase experiment
  5. 5. Phages Infecting a bacterium
  6. 6. Figure 16.1 Transformation of bacteria – Griffith (and later Avery, McCarty and MacLeod)
  7. 7. The Structure of DNA <ul><li>Nucleotide monomers: </li></ul><ul><ul><li>Phosphate </li></ul></ul><ul><ul><li>Pentose Sugar (C5) – Deoxyribose Sugar </li></ul></ul><ul><ul><li>Organic Nitrogen Base : </li></ul></ul><ul><ul><ul><li>Cytosine (C) </li></ul></ul></ul><ul><ul><ul><li>Adenine (A) </li></ul></ul></ul><ul><ul><ul><li>Guanine (G) </li></ul></ul></ul><ul><ul><ul><li>Thymine (T) </li></ul></ul></ul>
  8. 8. Structure of DNA cont’ <ul><li>Polynucleotide chain with linkage via phosphates to next sugar, with nitrogen base away from backbone of </li></ul><ul><li>Phos-sugar-phos-sugar </li></ul><ul><li>Dehydration synthesis </li></ul>
  9. 9. Beginning of the 1950’s several labs were studying the structure of DNA <ul><li>Maurice Wilkins & Rosalind Franklin </li></ul><ul><ul><li>X-ray crystallography: x-rays pass through pure DNA and diffraction of x-rays were then examined on film </li></ul></ul><ul><li>James Watson and Francis Crick did not have the expertise of Franklin and were without proper photos until……… </li></ul>
  10. 10. Figure 16.4 Rosalind Franklin and her X-ray diffraction photo of DNA
  11. 11. Watson and Crick
  12. 12. April 1953 – Classical one page paper in Nature by Watson and Crick <ul><li>A double helix – 2 polynucleotide strands </li></ul><ul><li>Sugar-phosphate chains of each strand are like the side ropes of a rope ladder </li></ul><ul><li>Pairs of nitrogen bases, one from each strand, form the rungs or steps </li></ul><ul><li>The ladder forms a twist every 10 bases (all from x-ray studies!) </li></ul>
  13. 13. Figure 16.5 The double helix
  14. 14. Internal Structure of DNA: Purine and pyridimine? REMEMBER X-RAY DATA
  15. 15. Confirms Erwin Chargaff’s Rules <ul><li># of Adenine = to # of thymine </li></ul><ul><li># of guanine equal to # of cytosine </li></ul><ul><li>This dictates the combinations of N-bases that form steps/rungs </li></ul><ul><li>Does not restrict the sequence of bases along each DNA strand </li></ul>
  16. 16. Information storage in DNA <ul><li>The 4 nitrogenous bases are the “alphabet” or code for all the traits the organism possesses </li></ul><ul><li>Different genes or traits vary the sequence and length of the bases </li></ul><ul><li>ATTTCGGAC vs. GGGATTCTAG vs. GATC </li></ul>
  17. 17. Replication/Duplication of DNA <ul><li>Due to complimentary base paring – one strand of DNA determines the sequence of the other strand </li></ul><ul><li>Therefore, each strand of double stranded DNA acts as a template </li></ul><ul><li>The double helix first unwinds – controlled by enzymes –and uses new nucleotides that are free in the nucleus to copy a complimentary strand off the original DNA strand </li></ul>
  18. 18. Figure 16.7 A model for DNA replication: the basic concept (Layer 1)
  19. 19. Figure 16.7 A model for DNA replication: the basic concept (Layer 2)
  20. 20. Figure 16.7 A model for DNA replication: the basic concept (Layer 3)
  21. 21. Figure 16.7 A model for DNA replication: the basic concept (Layer 4)
  22. 22. Figure 16.8 Three alternative models of DNA replication
  23. 23. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 1)
  24. 24. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 2)
  25. 25. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 3)
  26. 26. Figure 16.9 The Meselson-Stahl experiment tested three models of DNA replication (Layer 4)
  27. 27. There are a series of enzymes that control DNA replication – enzymes which: <ul><li>Uncoil the original double helix strand via a helicase </li></ul><ul><li>Single-strand binding protein keeps helix apart so replication can start </li></ul><ul><li>Prime an area to start replication – primase except it adds RNA nucleotides at first </li></ul><ul><li>Polymerase to join individual nucleotides (dehydration synthesis) </li></ul><ul><li>Ligases to join short segments </li></ul>
  28. 28. DNA REPLICATION
  29. 29. Figure 16.10 Origins of replication in eukaryotes
  30. 30. Figure 16.11 Incorporation of a nucleotide into a DNA strand
  31. 31. <ul><li>The carbons of the deoxyribose sugar are numbered </li></ul><ul><li>#3 carbon attached to an -OH group </li></ul><ul><li>#5 carbon holds the phosphate molecule of that nucleotide </li></ul><ul><li>#3 ready to bond with another nucleotide to form a polynucleotide link (5’ to3’) </li></ul><ul><li>Notice complimentary strand in opposite direction (5’ to 3’) </li></ul><ul><li>DNA always grows 5’ to 3’ never 3’ to 5’ </li></ul>Antiparallel Arrangement of Double Strands
  32. 32. Definitions <ul><li>Origins of Replication – where replication of the DNA molecule begins </li></ul><ul><ul><li>Bacteria – circular DNA – 1 origin of replication (RF) </li></ul></ul><ul><ul><li>Eukaryotes – multiple origins of replication (ORFS) </li></ul></ul><ul><ul><ul><li>ORF = Replication Fork </li></ul></ul></ul>
  33. 33. More Definitions <ul><li>DNA Polymerases – enzymes that catalyze DNA replication </li></ul><ul><li>Leading Strand – Synthesized continuously towards the replication fork by the DNA polymerase in one long fashion </li></ul><ul><li>Lagging Strand – Synthesized by short fragments away from the replication fork by the DNA polymerase </li></ul>
  34. 34. Definitions Cont’ <ul><li>Ligase – combines (joins) short fragments </li></ul><ul><li>Primer – starts replication of DNA (in this case it’s RNA) </li></ul><ul><li>Primase – an enzyme that joins the RNA nucleotides to make the primer </li></ul><ul><li>Helicase – an enzyme that untwists the double helix at the replication fork </li></ul><ul><li>Nuclease – a DNA cutting enzyme </li></ul>
  35. 35. DNA REPLICATION -VIDEO
  36. 36. Figure 16.13 Synthesis of leading and lagging strands during DNA replication
  37. 37. Figure 16.14 Priming DNA synthesis with RNA
  38. 38. Figure 16.15 The main proteins of DNA replication and their functions
  39. 39. Figure 16.16 A summary of DNA replication
  40. 40. Figure 16.17 Nucleotide excision repair of DNA damage
  41. 41. A PROBLEM! <ul><li>The end of the leading strand was initiated with an RNA primer </li></ul><ul><ul><li>Normally removed by other DNA polymerase </li></ul></ul><ul><li>Removal of gaps by DNA Polymerase doesn’t work on lagging strand end </li></ul><ul><ul><li>RNA primer removed with no replacement </li></ul></ul><ul><ul><li>A GAP! </li></ul></ul><ul><ul><li>SHORTER AND SHORTER FRAGMENTS? </li></ul></ul>
  42. 42. Prokaryotes have circular DNA – no problem at ends (there aren’t ANY! <ul><li>Eukaryotes – have special terminal sequences of 6 nucleotides that repeat from 100-1000 times with no genes included </li></ul><ul><ul><li>Telomers </li></ul></ul><ul><li>Protect more internal gene materials from being eroded </li></ul><ul><li>Germ cells / sex cells have a special enzyme (telomerase) that actually restore shortened Telomers </li></ul><ul><li>Somatic cells – telomer continues to shorten and may play a role in aged cell death </li></ul><ul><li>Cancer cells </li></ul><ul><ul><li>A telomerase prevents very short lengths </li></ul></ul>
  43. 43. Figure 16.19a Telomeres and telomerase: Telomeres of mouse chromosomes
  44. 44. Ribonucleic Acid (RNA) <ul><li>Structure of RNA </li></ul><ul><ul><li>Nucleotide monomer </li></ul></ul><ul><ul><ul><li>Phosphate </li></ul></ul></ul><ul><ul><ul><li>Pentose sugar = ribose (extra oxygen) </li></ul></ul></ul><ul><ul><ul><li>Nitrogenous base (A/G/C/U) </li></ul></ul></ul><ul><ul><ul><li>Single stranded </li></ul></ul></ul><ul><ul><ul><li>3 types (mRNA, tRNA, rRNA) </li></ul></ul></ul>
  45. 45. Synthesis of RNA - transcription <ul><li>DNA acts as a template, but only one strand of DNA utilized at a given time </li></ul><ul><li>This exposed strand is controlled by specific enzymes that pair the DNA nucleotides with free RNA nucleotides which are also present in the nucleus </li></ul><ul><li>These RNA nucleotides form a single stranded RNA nucleic acid </li></ul><ul><li>DNA = ATTGGCT </li></ul><ul><li>RNA = UAACCGA </li></ul><ul><li>Short segments of DNA are transcribed at a time with start and stop messages </li></ul>
  46. 46. Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic information (Layer 1)
  47. 47. Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic information (Layer 2)
  48. 48. Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic information (Layer 3)
  49. 49. Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic information (Layer 4)
  50. 50. Figure 17.2 Overview: the roles of transcription and translation in the flow of genetic information (Layer 5)
  51. 51. Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer 1)
  52. 52. Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer 2)
  53. 53. Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer 3)
  54. 54. Figure 17.6 The stages of transcription: initiation, elongation, and termination (Layer 4)
  55. 55. Figure 17.6 The stages of transcription: elongation
  56. 56. Three types of RNA <ul><li>mRNA : messenger RNA </li></ul><ul><ul><li>Transcribed from a specific segment of DNA which represents a specific gene or genetic unit </li></ul></ul><ul><li>tRNA : transfer RNA </li></ul><ul><ul><li>Transcribed from different segments of DNA and their function is to find a specific amino acid in the cytoplasm and bring it to the mRNA </li></ul></ul><ul><li>rRNA : ribosomal RNA </li></ul><ul><ul><li>Transcribed at the nucleolus - with proteins function as the site of protein synthesis </li></ul></ul>
  57. 57. Three types of RNA
  58. 58. Protein Synthesis = Translation <ul><li>Ribosomes = sites of protein synthesis </li></ul><ul><ul><li>30% - 40% protein </li></ul></ul><ul><ul><li>60% - 70% RNA (rRNA) </li></ul></ul><ul><ul><li>Assembled in nucleus and exported via nuclear pores </li></ul></ul><ul><ul><li>Antibiotics can paralyze bacterial ribosomes, but not eukaryotic ribosomes (not targeting them) </li></ul></ul><ul><ul><li>2 ribosomal subunits –a large and a small </li></ul></ul><ul><ul><li>Small subunit has been used as a means of classifying different bacteria and different invertebrates (16S) </li></ul></ul><ul><ul><ul><li>Eukaryotes – 18S </li></ul></ul></ul><ul><ul><li>There are three sites on the ribosome that are involved in protein synthesis </li></ul></ul>
  59. 59. Ribosomes bring mRNA together with amino acid bearing tRNA’s <ul><li>Three ribosomal sites </li></ul><ul><ul><li>P Site (peptidyl-tRNA) holds the tRNA carrying the growing peptide chain after several amino acids have been added </li></ul></ul><ul><ul><li>A site (aminoacyl-tRNA) holds the next single amino acid to be added to the chain </li></ul></ul><ul><ul><li>E site (exit site) site where discharged tRNA minus amino acids leave ribosome </li></ul></ul>
  60. 60. Figure 17.15 Translation – the basic concept
  61. 61. Preparation of Eukaryotic mRNA <ul><li>RNA splicing- a cut and paste job to remove nucleotides from transcribed mRNA </li></ul><ul><ul><li>8000 nucleotides transcribed but the average gene contains 1200+ nucleotides </li></ul></ul><ul><ul><li>Long non-coding segments (introns) interspersed between coding segments (exons) expressed via amino acids </li></ul></ul>
  62. 63. Figure 17.17 The initiation of translation
  63. 64. Figure 17.18 The elongation cycle of translation
  64. 65. Protein Synthesis (cont’) Initiation – elongation - termination <ul><li>Starting at one end of the mRNA, the small ribosomal subunit associates with the mRNA and accepts the first tRNA with its activated amino acid attached = Initiation </li></ul><ul><li>tRNA associate with a triplet codon exposed on the mRNA – these are 3 nitrogenous bases that bond with 3 complementary bases exposed (anticodon) on the tRNA opposite the attached amino acid </li></ul><ul><li>Wobble </li></ul><ul><ul><li>Aren’t 61 tRNAs, are 54tRNAs </li></ul></ul>
  65. 66. Figure 17.4 The dictionary of the genetic code
  66. 67. Figure 17.3 The triplet code
  67. 68. tRNA complexes with its amino acid in the cytoplasm using ATP – activated tRNA <ul><li>The activated tRNA-amino acid complex moves towards the ribosomal area and finds a triplet codon exposed that is complementary to the anticodon of the tRNA </li></ul><ul><li>The first activated tRNA-amino acid, after its anticodon is bound to the mRNA codon, associates with the large ribosomal subunit which now joins the smaller subunit and the mRNA and the tRNA (TAKE A BREATH!) </li></ul>
  68. 69. The first tRNA and its amino acid now occupy the P site of the large ribosomal subunit <ul><li>Review – at this point the 2 part ribosome is assembled, the mRNA has started to be read, and one tRNA plus amino acid is occupying the P site </li></ul><ul><li>That means the adjacent A site is free to accept a second activated tRNA and its amino acid, but only if the anticodon of this tRNA matches the next three base pairs exposed (codon) </li></ul>
  69. 70. Protein Synthesis (continued) <ul><li>At this point, there are 2 tRNA-amino acid complexes adjacent to each other – Elongation involved one amino acid being added in a three step process: </li></ul><ul><ul><li>Codon recognition – the mRNA codon in the A site matches with the anticodon of the tRNA –amino acid complex </li></ul></ul><ul><ul><li>Peptide bond formation between the new amino acid in the A site and the amino acid (later peptide) in the P site </li></ul></ul><ul><ul><li>Translocation </li></ul></ul>
  70. 71. Translocation – the ribosome moves the tRNA into the A site, and its attached peptide to the P site, as the previous tRNA from the P site moves to the E (Exit) site and leaves the ribosome <ul><li>Review: once this process is under way, an activated tRNA with its amino acid finds an exposed codon in the A site, attaches via H-bonds, then forms a peptide bond with the polypeptide associated with the tRNA sitting in the adjacent P site. For a moment, the longer polypeptide chain is only attached to the tRNA in the A site. Now the entire ribosome shifts so that the……… </li></ul>
  71. 72. Yet More Protein Synthesis <ul><li>The empty tRNA from the P site moves in to the E site and leaves the ribosome </li></ul><ul><li>As the tRNA with the polypeptide chain moves from the A site to the now empty P site ….exposing a new codon. </li></ul><ul><ul><li>GUESS WHAT HAPPENS NEXT?! </li></ul></ul>
  72. 73. A question? <ul><li>Every time a new codon is exposed in the A site, a specific tRNA-AA complex moves into the site. What originally determined this mRNA Codon? </li></ul>
  73. 74. The Answer! <ul><li>The original DNA that was transcribed </li></ul><ul><li>This elongation of 1 AA takes about 0.1 s </li></ul><ul><li>Termination – the above continues (dozens to hundreds or more AA added) until the STOP CODON is reached (codon at the end of the mRNA) </li></ul><ul><li>This codon does not have a matching tRNA anticodon so the tRNA-AA attaches in the A site and the tRNA moves to the E site and releases the polypeptide chain </li></ul>
  74. 75. FINALLY - SUMMARY <ul><li>The take home message: </li></ul><ul><ul><li>At the ribosome, the genetic language of DNA is translated into a different language – Via RNA – into the functioning language of PROTEINS!!!! </li></ul></ul>
  75. 76. Figure 17.17 The initiation of translation
  76. 77. Figure 17.18 The elongation cycle of translation
  77. 78. Figure 17.19 The termination of translation
  78. 79. Figure 17.20 Polyribosomes
  79. 80. Table 17.1 Types of RNA in a Eukaryotic Cell
  80. 81. Figure 17.23 The molecular basis of sickle-cell disease: a point mutation
  81. 82. Figure 17.24 Categories and consequences of point mutations: Base-pair insertion or deletion
  82. 83. Figure 17.24 Categories and consequences of point mutations: Base-pair substitution
  83. 84. Figure 17.25 A summary of transcription and translation in a eukaryotic cell
  84. 85. Figure 18.19 Regulation of a metabolic pathway
  85. 86. Control of Protein Synthesis Regulation of Gene Expression <ul><li>Every cell has the same numbers and types of chromosomes </li></ul><ul><li>Development and normal gene function requires precise gene expression in an on and off manner </li></ul><ul><li>Operon – cluster of gene segments on DNA and its controlling segments </li></ul><ul><ul><li>Repressible </li></ul></ul><ul><ul><li>Inducible </li></ul></ul>
  86. 87. Regions of the Operon (DNA) <ul><li>Promoter region : promotes transcription by binding with RNA polymerase </li></ul><ul><li>Operator region : binds a regulatory protein or chemical </li></ul><ul><ul><li>Overlaps with the RNA polymerase binding site </li></ul></ul><ul><li>Structural genes : code for a particular peptide or several peptides </li></ul><ul><ul><li>Start or stop codes </li></ul></ul>
  87. 88. Figure 18.20a The trp operon: REPRESSIBLE
  88. 89. Figure 18.21a The lac operon: INDUCIBLE
  89. 90. Figure 19.7 Opportunities for the control of gene expression in eukaryotic cells
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