Intro chapter 10 part2a

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Intro chapter 10 part2a

  1. 1. Chapter 10 <ul><li>Molecular Biology of the Gene </li></ul><ul><li>Part 2 </li></ul>
  2. 2. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Now that we understand (hopefully) how the DNA replicates, we can finally begin to discuss how the genes work . </li></ul><ul><li>We already know that the gene controls the making of a protein . </li></ul><ul><li>This process is called protein synthesis . </li></ul>
  3. 3. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Before discussing the process itself, it is important to understand that the genes are in the nucleus and the protein building apparatus ( ribosomes) are in the cytoplasm. </li></ul>
  4. 4. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>DNA cannot leave the nucleus. It is too large a molecule to pass through the pores in the nuclear membrane. </li></ul><ul><li>Getting the information from the gene to the ribosome is done by a “middleman.” </li></ul><ul><li>This is RNA. </li></ul>
  5. 5. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>There are 3 types of RNA. Each has a specific role in the process of protein construction. </li></ul><ul><li>The 3 types are: </li></ul><ul><li>Ribosomal RNA (rRNA) </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>Messenger RNA (mRNA) </li></ul>
  6. 6. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Ribosomal RNA (rRNA) </li></ul><ul><li>Ribosomal RNA combines with protein to form the ribosomes. </li></ul><ul><li>Each ribosome is composed of 2 subunits . </li></ul><ul><li>These subunits fit together like two beans face to face, so there is a little opening between them. </li></ul>
  7. 7. Ribosome with tRNA and mRNA and the growing polypeptide.
  8. 8. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Ribosomal RNA </li></ul><ul><li>There are 2 active sites (transfer RNA binding sites) on the ribosome that allow the amino acids to line up and attach to each other. </li></ul><ul><li>These 2 sites are called the A site (where the amino acid comes in) and the P site (where the amino acid is added to the polypeptide chain). </li></ul><ul><li>Ribosomal RNA is the factory or the assembly line for manufacturing protein. </li></ul>
  9. 10. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>Transfer RNA is a highly motile form of RNA . It moves throughout the cytoplasm picking up amino acids and taking them to the ribosome. </li></ul><ul><li>tRNA is the truck that carries the raw materials (amino acids) to the factory. </li></ul>
  10. 11. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>tRNA has an unusual shape. </li></ul><ul><li>It is somewhat similar in shape to an upside down 3 leaf clover , although it is twisted around itself making it hard to see this clover shape. </li></ul>
  11. 12. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>There are two sites of importance in the tRNA. </li></ul><ul><li>At the top of the molecule is a site where the amino acid attaches . Each tRNA can carry </li></ul><ul><li>only a single specific amino acid. There are 22 different amino acids and more than 60 different tRNAs, so there is some overlap. </li></ul>
  12. 13. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>At the bottom of the molecule are 3 nitrogen bases called the anticodon . These 3 bases have 2 jobs. </li></ul><ul><li>1. They determine which specific amino acid can be carried by that tRNA. </li></ul><ul><li>2. They line up with the mRNA codons (3 complementary bases on the mRNA) so the amino acid is brought to the right place in the protein. </li></ul>
  13. 14. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Transfer RNA (tRNA) </li></ul>
  14. 15. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Messenger RNA (mRNA) </li></ul><ul><li>Messenger RNA carries the genetic information to the ribosome. It is the blueprint for the process of building the protein. </li></ul><ul><li>mRNA is a simple straight chain of nucleotides. </li></ul><ul><li>It is composed of a cap, exons, introns and a tail . </li></ul>
  15. 16. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Messenger RNA (mRNA) </li></ul><ul><li>Not all of the mRNA is needed to code for the protein. </li></ul><ul><li>The cap allows the mRNA to feed into the ribosome. </li></ul><ul><li>Introns are extraneous bits of material that must be edited out before the mRNA can be used. </li></ul>
  16. 17. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Messenger RNA (mRNA) </li></ul><ul><li>The tail stabilizes the mRNA as the last bits of it feed into the ribosome so it doesn’t fall out too soon. </li></ul><ul><li>The exons carry the code that is needed to make the protein. There are parts of the exons that are unused. These parts just add to the cap and tail. </li></ul>
  17. 18. Molecular Genetics cap intron exon 2 intron exon3 intron exon4 tail exon1 This represents a newly made mRNA molecule. It has not yet been edited.
  18. 19. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>Messenger RNA (mRNA) </li></ul><ul><li>The nucleotides in the body or the translational portion of the mRNA are functionally (not structurally) divided into groups of 3. </li></ul><ul><li>These groups are called codons. </li></ul><ul><li>Each codon calls for a specific amino acid at a specific spot in the amino acid chain. </li></ul>
  19. 20. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>So, now we have all the players for the process of protein synthesis. </li></ul><ul><li>rRNA is the factory , with all the enzymes and binding sites needed for protein assembly. </li></ul><ul><li>tRNA is the truck , carrying the amino acids to the docking sites in the factory. </li></ul><ul><li>mRNA is the blueprint , telling the tRNAs which amino acid to bring in at each point. </li></ul><ul><li>Lets begin the process. </li></ul>
  20. 21. Molecular Genetics <ul><li>Protein Synthesis </li></ul><ul><li>There are 2 parts to protein synthesis. </li></ul><ul><li>1. transcription = the building of the mRNA </li></ul><ul><li>2. translation = the building of the amino acid chain (polypeptide or protein). </li></ul>
  21. 22. Molecular Genetics <ul><li>Part 1: Transcription </li></ul><ul><li>Transcription is similar to DNA replication. There are a few differences: </li></ul><ul><li>A) Only a small part of the DNA opens (not all). </li></ul><ul><li>B) Only one strand (the template or 3  5 strand) of the open portion of DNA is copied. </li></ul>
  22. 23. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>C) RNA polymerase and RNA nucleotides are used rather than DNA polymerase and DNA nucleotides. </li></ul><ul><li>(RNA nucleotides have a different sugar (ribose) than DNA nucleotides and RNA does not use the base, thymine…but uses uracil instead). </li></ul><ul><li>D) Once the mRNA is made , it leaves the DNA and the DNA closes back up. </li></ul>
  23. 24. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>The process </li></ul><ul><li>RNA polymerase attaches to the DNA molecule triggering the DNA to open at a specific site where the gene of interest is located. </li></ul>
  24. 25. RNA polymerase Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A
  25. 26. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A
  26. 27. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>Once the DNA has opened, RNA nucleotides begin to line up with their complementary bases on the Template strand of the DNA. Remember, RNA has uracil instead of thymine. </li></ul><ul><li>When joining DNA nucleotides to RNA nucleotides the following bases make complementary pairs. </li></ul><ul><li>DNA to RNA </li></ul><ul><li>Adenine – Uracil </li></ul><ul><li>Thymine – Adenine </li></ul><ul><li>Cytosine – Guanine </li></ul><ul><li>Guanine – Cytosine </li></ul>
  27. 28. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C
  28. 29. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>The polymerase runs down the template strand, connecting the sugar-phosphate backbone of the newly forming messenger RNA strand. </li></ul>
  29. 30. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G
  30. 31. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C
  31. 32. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A
  32. 33. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U
  33. 34. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A
  34. 35. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G
  35. 36. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C
  36. 37. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A
  37. 38. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U
  38. 39. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C
  39. 40. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A
  40. 41. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G
  41. 42. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U
  42. 43. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C
  43. 44. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G
  44. 45. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G A
  45. 46. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G A C
  46. 47. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>Once the messenger RNA is completed, the polymerase leaves the DNA . </li></ul><ul><li>The newly formed mRNA leaves the DNA </li></ul><ul><li>The DNA simply closes back up as it was before. </li></ul>
  47. 48. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G A C
  48. 49. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G A C
  49. 50. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A U G A C G C A U A G C A U C A G U C G A C
  50. 51. Transcription A G T C G C A A T C T G A T G C T A T G C C A C T T C A G G C T T A G A C T A C G A T A C G G T G A G C A U A G C A U C A G U C G A C
  51. 52. Molecular Genetics <ul><li>Transcription </li></ul><ul><li>Before the new mRNA leaves the nucleus, it has to be edited , removing the introns and rejoining the exons so that the mRNA leaves the nucleus as a “ mature” mRNA molecule. </li></ul>
  52. 53. Molecular Genetics cap intron exon 2 intron exon3 intron exon4 tail exon1 Newly made “immature” mRNA A mature mRNA molecule ready to leave the nucleus and move to the ribosome to produce protein. Editing involves cutting out and discarding introns , then rejoining the exons.
  53. 54. Molecular Genetics <ul><li>Part 2: Translation </li></ul><ul><li>Before we can understand the process of translation, we need a better understanding of the codons on the mRNA. </li></ul><ul><li>Each codon is composed of three bases and codes for a single, specific amino acid . </li></ul><ul><li>Because the codons are lined up in an exact order, they call for the amino acids to be lined up in an exact order as well. </li></ul>
  54. 55. Molecular Genetics <ul><li>Translation </li></ul><ul><li>The next slide is a codon chart which tells us what amino acid each codon codes for. </li></ul><ul><li>If we know the sequence of bases on the template DNA strand, we can determine the complementary sequence of bases on the mRNA codons. </li></ul><ul><li>If we know the codon sequence , we can determine the amino acid sequence for the protein. </li></ul>
  55. 56. Codon Translation Chart
  56. 57. Molecular Genetics <ul><li>Translation </li></ul><ul><li>As you look at the chart, along the left side are letters that represent the 1 st base of the codon. </li></ul><ul><li>Across the top are additional letters that represent the 2 nd base of the codon. </li></ul><ul><li>Down the right hand side of the chart are the letters that represent the 3 rd base of each codon. </li></ul><ul><li>So, if you have the codon CGA, find C on the left, then U on top and then A on the right. Where these three letters come together, you will find the amino acid that is called for by this codon. </li></ul>
  57. 58. Codon Translation Chart
  58. 59. Molecular Genetics <ul><li>Translation </li></ul><ul><li>There are 4 special codons . </li></ul><ul><li>AUG is the start codon. </li></ul><ul><li>AUG calls for the amino acid, methionine , but the first AUG on the mRNA is also the start codon. It tells the ribosome when to start reading the mRNA and bringing in amino acids. </li></ul><ul><li>There are also 3 stop codons: UAA, UAG and UGA . </li></ul><ul><li>Stop codons do not code for any amino acid. They tell the ribosome to stop adding amino acids…the chain is complete. </li></ul>
  59. 60. Molecular Genetics <ul><li>Translation </li></ul><ul><li>The process </li></ul><ul><li>The mature mRNA leaves the nucleus and moves to the ribosomes. The cap threads into the ribosome and mRNA passes through until a codon bearing the 3 bases AUG enters the A site. </li></ul><ul><li>AUG is the start codon. It triggers the ribosome to start building the protein. </li></ul><ul><li>AUG also codes for the amino acid, Methionine. </li></ul><ul><li>Methionine is always the first amino acid in any protein or polypeptide. </li></ul>
  60. 61. Translation The mRNA moves to the ribosome. It threads its way along, codon by codon … ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A
  61. 62. Translation until the A site lines up with the first AUG on the mRNA. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A
  62. 63. Translation ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A With the first AUG codon at the A site, a tRNA comes into the ribosome with the anticodon that complements the codon (in this case, UAC). The tRNA carries the first amino acid, Methionine and the process of translation begins. UAC met
  63. 64. Translation ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A Once the tRNA has hooked onto the codon, the mRNA shifts so that the codon with the tRNA moves to the P site . UAC met
  64. 65. Translation A new tRNA will now move to the codon at site A . In this example, its anticodon will have to be AAA and it will carry the amino acid, phenylalanine. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UAC met
  65. 66. Translation Now the amino acids are in close proximity and an enzyme in the ribosome links the two amino acids together. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UAC met AAA phe
  66. 67. Translation The tRNA at site P releases its hold on both its amino acid and the codon and leaves the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UAC met AAA phe
  67. 68. Translation Again the mRNA shifts on the ribosome and a new tRNA will come into site A. met ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UAC AAA phe
  68. 69. Translation The amino acids at site P will attach to the new amino acid at site A and the tRNA at site P will detach and leave the ribosome. met ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A AAA phe GCG arg
  69. 70. Translation The mRNA shifts again and another tRNA comes to the ribosome. met phe ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A AAA GCG arg
  70. 71. Translation met phe The amino acids at site P will attach to the new amino acid at site A and the tRNA at site P will detach and leave the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A GUG arg ACC trp
  71. 72. Translation met phe arg The mRNA shifts again and another tRNA comes to the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A GUG ACC trp
  72. 73. Translation met phe arg The amino acids at site P will attach to the new amino acid at site A and the tRNA at site P will detach and leave the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A ACC trp UUG asn
  73. 74. Translation The mRNA shifts again and another tRNA comes to the ribosome. met phe arg trp ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A ACC UUG asn
  74. 75. Translation met phe arg trp The amino acids at site P will attach to the new amino acid at site A and the tRNA at site P will detach and leave the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UUG asn GUC gln
  75. 76. Translation met phe arg trp asn The mRNA shifts again and another tRNA comes to the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A UUG GUC gln
  76. 77. Translation met phe arg trp asn GUC gln The amino acids at site P will attach to the new amino acid at site A and the tRNA at site P will detach and leave the ribosome. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A AUG tyr
  77. 78. Translation met phe arg trp asn gln The mRNA shifts again. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A GUC AUG tyr
  78. 79. Translation met phe arg trp asn gln We have now reached a STOP codon . It codes for no amino acid, so there is no amino acid for the chain to attach to. Thus, when the tRNA at P is released, the polypeptide is also released. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A AUG tyr
  79. 80. Translation ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A AUG met phe arg trp asn gln tyr
  80. 81. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A met phe arg trp asn gln tyr
  81. 82. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A met phe arg trp asn gln tyr
  82. 83. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A met phe arg trp asn gln tyr
  83. 84. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A met phe arg trp asn gln tyr
  84. 85. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA P A met phe arg trp asn gln tyr
  85. 86. Translation The mRNA will finish its journey through the ribosome and may then be used again to make another copy or it may be broken down by the cell. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA
  86. 87. Complementary Base Pairing Given the DNA template strand, you can determine the complementary strand , the mRNA , the anticodons on the tRNA and with a chart, the amino acid sequence . Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT Complementary DNA strand ACT CCG ATG TTT CGC TGG AAC CAG TAC TAG CCA TAC AAA
  87. 88. Complementary Base Pairing Given the DNA template strand, you can determine the complementary strand…. Complementary DNA strand ACT TGG CCG ATG TTT CGC AAC TAC CAG TAC TAG CCA AAA DNA to DNA ADENINE - THYMINE THYMINE - ADENINE GUANINE - CYTOSINE CYTOSINE - GUANINE Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT
  88. 89. Complementary Base Pairing the mRNA codons… ACU UGG CCG AUG UUU CGC AAC UAC CAG UAC UAG CCA AAA mRNA DNA to RNA ADENINE - URACIL THYMINE - ADENINE GUANINE - CYTOSINE CYTOSINE - GUANINE Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT Complementary DNA strand ACT CCG ATG TTT CGC TGG AAC CAG TAC TAG CCA TAC AAA
  89. 90. Complementary Base Pairing The tRNA anticodons… RNA to RNA ADENINE - URACIL URACIL - ADENINE GUANINE - CYTOSINE CYTOSINE - GUANINE ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT Complementary DNA strand ACT CCG ATG TTT CGC TGG AAC CAG TAC TAG CCA TAC AAA UAC GCG ACC UUG GUC AUG AAA
  90. 91. Complementary Base Pairing and, with the codon chart, the amino acid sequence. ACU CCG AUG UUU CGC UGG AAC CAG UAC UAG CCA UAC AAA Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT Complementary DNA strand ACT CCG ATG TTT CGC TGG AAC CAG TAC TAG CCA TAC AAA met phe arg trp asn tyr gln UAC GCG ACC UUG GUC AUG AAA
  91. 92. Mutations <ul><li>When discussing Chromosomes and Genetics, we have mentioned mutations that can occur on our DNA. </li></ul><ul><li>We will now look at how these mutations work. </li></ul>
  92. 93. Mutations <ul><li>1. Point Mutations </li></ul><ul><li>A point mutation alters a single nucleotide on the DNA molecule. There are 2 basic types of point mutations: </li></ul><ul><li>a) substitution mutations </li></ul><ul><li>b) frame shift mutations </li></ul>
  93. 94. Mutations <ul><li>1. Point Mutations </li></ul><ul><li>a) substitution mutations </li></ul><ul><li>In a substitution mutation, one nitrogen base in the original DNA sequence is replaced with a different nitrogen base. </li></ul><ul><li>There are 3 possible consequences of this substitution. </li></ul>
  94. 95. Mutations <ul><li>1. Point Mutations </li></ul><ul><li>a) substitution mutations </li></ul><ul><li>(i) A silent mutation occurs if the base change does not cause a change in the amino acid at that point in the protein. (This occurs most often when the 3 rd base of a codon is altered). </li></ul><ul><li>(ii) A missense mutation occurs if the base change causes a single amino acid to change in the polypeptide sequence. (This can occur with a change in the 1 st , 2 nd and sometimes the 3 rd base of the codon). </li></ul><ul><li>(iii) A nonsense mutation occurs if the substitution causes the codon to change to a stop codon which causes the polypeptide or protein to cut off before it is complete. </li></ul>
  95. 96. Point mutations 1.Substitution a. silent Mutated mRNA Original A.A. sequence Mutated A.A. sequence ACU CCG AUG UUU CGC UGG AA U CAG UAC UAG CCA UAC AAA Mutated Template DNA strand TGA GGC TAC AAA GCG ACC TT A GTC ATG ATC GGT ATG TTT met phe arg trp asn tyr gln Original Template DNA strand TGA GGC TAC AAA GCG ACC TT G GTC ATG ATC GGT ATG TTT met phe arg trp asn tyr gln
  96. 97. Point mutations 1.Substitution b. missense Mutated mRNA Original A.A. sequence Mutated A.A. sequence ACU CCG AUG UUU CGC UGG AA A CAG UAC UAG CCA UAC AAA Mutated Template DNA strand TGA GGC TAC AAA GCG ACC TT T GTC ATG ATC GGT ATG TTT met phe arg trp asn tyr gln Original Template DNA strand TGA GGC TAC AAA GCG ACC TT G GTC ATG ATC GGT ATG TTT met phe arg trp lys tyr gln
  97. 98. Point mutations 1.Substitution c. nonsense Mutated mRNA Original A.A. sequence Mutated A.A. sequence stop ACU CCG AUG UUU CGC U A G AAG CAG UAC UAG CCA UAC AAA Mutated Template DNA strand TGA GGC TAC AAA GCG A T C TTG GTC ATG ATC GGT ATG TTT met phe arg trp asn tyr gln Original Template DNA strand TGA GGC TAC AAA GCG A C C TTG GTC ATG ATC GGT ATG TTT met phe arg
  98. 99. Mutations <ul><li>1. Point Mutations </li></ul><ul><li>b) Frameshift mutations </li></ul><ul><li>If a single base is deleted or added to the DNA nucleotide sequence, it changes the mRNA codons in such a way that all of the codons beyond that point are altered . This can have serious consequences on the functionality of the resulting protein. </li></ul>
  99. 100. Point mutations 2. Frame shift a. addition Mutated mRNA Original A.A. sequence leu ala Mutated A.A. sequence ACU CCG AUG UUU CGC UGG AAC U CA GUA CUA GCC AUA CAA A Mutated Template DNA strand TGA GGC TAC AAA GCG ACC TTG A GT CAT GAT CGG TAT GTT T met phe arg trp asn tyr gln Original Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT met phe arg trp asn gly ser ile gln
  100. 101. Point mutations 2. Frame shift b. deletion Mutated mRNA Original A.A. sequence ser his Mutated A.A. sequence ACU CCG AUG UUU CGC UGG AAC A GU ACU AGC CAU ACA AA Mutated Template DNA strand TGA GGC TAC AAA GCG ACC TTG TC A TGA TCG GTA TGT TT met phe arg trp asn tyr gln Original Template DNA strand TGA GGC TAC AAA GCG ACC TTG GTC ATG ATC GGT ATG TTT met phe arg trp asn thr ser thr

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