Chapter 16: Review Molecular Basis of Inheritance <ul><li>Search for genetic material led to DNA </li></ul><ul><li>Discove...
Chapter 17:  From Gene to Protein <ul><li>Study of metabolic defects provided evidence that genes specify proteins </li></...
<ul><li>Transcription is the DNA-directed synthesis of RNA </li></ul><ul><li>Signal peptides target some eukaryotic polype...
<ul><li>A point mutation can affect the function of a protein </li></ul><ul><li>Ask again, what is a gene? </li></ul>
Study of Metabolic Defects Provided Evidence that Genes Specify Proteins <ul><li>Archibald Garrod  (1909) proposed relatio...
How Do Genes Control Metabolism <ul><li>Beadle & Tatum </li></ul><ul><li>Red bread mold (maybe you know it) </li></ul><ul>...
Neurospora  - Red Bread Mold
<ul><li>They concluded that each mutant was defective in a single gene coding for one enzyme. </li></ul><ul><li>This lead ...
Modified Idea <ul><li>This idea was modified to be  one gene-one polypeptide hypothesis  because: not all proteins are enz...
Transcription & Translation:  Two Main Steps from Gene to Protein <ul><li>Genes are the instructions for making specific p...
DNA & RNA: Both Polymers <ul><li>Both RNA & DNA are nucleotide polymers with two main differences: deoxyribose of DNA has ...
DNA & RNA Structural Differences
<ul><li>Flow of information  - gene to protein, is described in  linguistic terms  because both nucleic acids and proteins...
<ul><li>DNA/RNA - monomers are the four types of nucleotides (nitrogenous bases differ) that are 100’s or 1000’s of nucleo...
<ul><li>A protein has monomers in a particular linear order, but the monomers are......? </li></ul>
Amino Acids <ul><li>Amino acids..20 of them. </li></ul><ul><li>Thus, nucleic acids & proteins contain information written ...
<ul><li>Getting from one to the other requires two major steps: Transcription   and  Translation </li></ul>
Transcription <ul><li>Transcription  is the synthesis of RNA under the direction of DNA (template...recall replication). B...
<ul><li>The RNA molecule made according to the DNA template is a transcript of the gene’s protein-building instructions. <...
<ul><li>This RNA is called  mRNA (messenger RNA) , which functions as a genetic message from DNA to the protein-synthesizi...
<ul><li>Translation  is the actual synthesis of a polypeptide, which occurs under the direction of mRNA. </li></ul>
<ul><li>There is a  change in language  from the base sequence of an mRNA into the amino acid sequence of a polypeptide. <...
<ul><li>Ribosomes  are the sites of  translation , which are made of numerous enzymes & other agents that facilitate the o...
Prokaryote/Eukaryote Difference? <ul><li>Bacteria lack a nuclei, so DNA is not segregated from ribosomes, etc.  </li></ul>...
Prokaryotic Cell Immediate Translation No Nucleus
Eukaryotic Cell Nucleus RNA  Processing
<ul><li>DNA  RNA  Protein </li></ul>
Genetic Code: Nucleotide Triplets Specify Amino Acids <ul><li>Only four nucleotides code for 20 amino acids. </li></ul>
Codon <ul><li>Three nucleotide “words” are called codons. </li></ul><ul><li>Codon =three-nucleotide sequence in mRNA that ...
Recall....... <ul><li>Genes are not directly translated into amino acids, but are first transcribed as codons into mRNA. <...
<ul><li>An  mRNA is complementary  to the DNA template from which it is transcribed, for example, the DNA sequence CCG is ...
Triplet Code DNA mRNA Amino Acid
Fig. 17.4 Triplet code. <ul><li>Each mRNA codon specifies which one of the 20 amino acids will be incorporated into a corr...
Cracking the Genetic Code <ul><li>By the mid-1960s all 64 codons were known. Figure 17.4 is the dictionary of the genetic ...
GENETIC CODE AUG Met. = Start Stop= UAA UAG UGA
Factoid <ul><li>AUG that codes for methionine (Met, start signal or initiation codon) is sometimes removed subsequently. <...
<ul><li>There is  redundancy  in the code....several codons for one amino acid, but there is  no ambiguity  (same codon fo...
Reading Frame <ul><li>Reading frame  = correct grouping of adjacent nucleotide triplets into codons that are in the correc...
Reading frame <ul><li>THE  BIG  RED  CAT  ATE  THE  BIG  BAD  FAT  RAT. </li></ul><ul><li>HEB  IGR  EDC  ATA  TET  HEB  IG...
<ul><li>My codon is A D D. </li></ul><ul><ul><li>A ttention </li></ul></ul><ul><ul><li>D eficit </li></ul></ul><ul><ul><li...
The Genetic Code <ul><li>The genetic code is nearly universal - a language that is shared across all of life meaning it mu...
Transcription Up Close Transcription is the DNA-Directed Synthesis of RNA <ul><li>RNA polymerases pry apart the two DNA st...
<ul><li>DNA that is transcribed into an RNA molecule is the  TRANSCRIPTION  UNIT . </li></ul>
Transcription Up Close <ul><li>Prokaryotes have one RNA polymerase. Eukaryotes have three. </li></ul><ul><li>mRNA synthesi...
RNA Polymerase Binding & Initiation <ul><li>RNA polymerases bind to DNA regions called  PROMOTORS . </li></ul>
<ul><li>Promoter  = initiation site + dozens of nucleotides “upstream” from initiation site.  e.g. TATA box (eukaryotes) a...
<ul><li>TRANSCRIPTION FACTORS  - aid polymerases in finding promotor regions on DNA (sometimes attach before polymerase ca...
Elongation <ul><li>RNA polymerase II untwists DNA one turn (helix) at a time exposing 10 bases for pairing of RNA nucleoti...
<ul><li>mRNA peels away as the noncoding strand reforms the double helix. </li></ul>
<ul><li>A single gene can be transcribed simultaneously by several polymerase IIs so it can produce proteins faster (more ...
Termination <ul><li>RNA polymerase transcribes until termination site is reached (AAAAAA in eukaryotes). </li></ul><ul><li...
Figure 17.6
Figure 17.7 Initiation of  Transcription at a Eukaryotic Promoter
Eukaryotic Cell Modify RNA after Transcription <ul><li>Alternation of mRNA Ends </li></ul><ul><li>Split Genes and RNA Spli...
RNA Processing : Both ends  (5’ & 3’) are modified, then cut apart & spiced together again <ul><li>Alteration of mRNA ends...
<ul><li>- 3’ Poly-A tail (several hundred adenines) for protection & transport from nucleus to cytoplasm. </li></ul>
RNA Processing:  Add Cap & Tail 5’Cap 3’Tail
RNA Processing :  <ul><li>RNA splicing - Average DNA molecule is 8000 bases, RNA in nucleus is same length, but 1200 nucle...
<ul><li>What happened to the 6,800 nucleotides between the nucleus and cytoplasm....? </li></ul>
RNA Processing :  <ul><li>INTRONS  - intervening noncoding segments of DNA are transcribed then removed. </li></ul>
<ul><li>EXONS  - are coding regions that are express eventually (translated into proteins).  </li></ul><ul><li>RNA splicin...
RNA Processing: Splicing Transcription Introns Excised Exons Spliced
Play CD
Synthesis of Protein Translation Up Close (p. 304) <ul><li>In the  Process of Translation  a cell  interprets a genetic me...
TRANSFER RNA  <ul><li>tRNA transfers amino acids from the cytoplasm’s amino acid pool to the ribosome .  </li></ul><ul><li...
<ul><li>Some 45 different tRNA molecules associate with particular mRNA codons that code for amino acids. </li></ul>
Translation Up Close <ul><li>On one end is a tRNA’s particular amino acid, on the other end is a base triplet called an  A...
Transfer RNA <ul><li>tRNAs are transcribed in the nucleus from DNA templates (nucleus) then travel to cytoplasm for transl...
<ul><li>Some tRNAs have anticodons that recognize two or more codons. The third base pairings (between anticodon & mRNA) a...
<ul><li>This relaxation of base-pairing rules is called  WOBBLE .  Explains synonymous codons for certain amino acids. </l...
<ul><li>See Figure 17.13 for aminoacyl-tRNA synthase joining a tRNA to an amino acid...... </li></ul>
Ribosomes <ul><li>Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis....
Building a Polypeptide <ul><li>Initiation>Elongation> Termination </li></ul>
Building a Polypeptide <ul><li>Initiation  :  mRNA + tRNA (with amino acid) + two ribosomal subunits + GTP (energy). </li>...
Initiation of Translation
Building a Polypeptide <ul><li>Elongation : Codon recognition (+GTP) > Peptide bond formation (peptidyl transferase) & rel...
Elongation of Translation Codon Recognition Peptide Bond Formation
Building a Polypeptide <ul><li>Translocation : tRNA dissociates from ribosome....mRNA & ribosome move in unison (ratchet-l...
Elongation of Translation Translocation A  Site P  Site
Building a Polypeptide <ul><li>Termination : Elongation until  TERMINATION   CODON  reached (UAA, UAG, UGA - not amino aci...
Termination of Translation Free Polypeptide Termination Codon Ribosome  Dissociation
Play CD
Building a Polypeptide <ul><li>POLYRIBOSOMES  - more than one ribosome translating on same mRNA molecule  (Figure 17.18 in...
Signal Peptides <ul><li>Free (cytosol) & bound (to endoplasmic reticulum) ribosomes -  Free  - proteins in cytosol Bound  ...
<ul><li>SIGNAL SEQUENCE  - on peptide enables ribosome to attach to receptor site on ER membrane (signal seq. is eventuall...
Signal Mechanism for  Targeting Proteins Signal Recognition  Particle Signal Sequence Receptor Site Endoplasmic Reticulum
Types of RNA in a Eukaryote See Table 17.1 <ul><li>Messenger RNA </li></ul><ul><li>Transfer RNA </li></ul><ul><li>Ribosoma...
Mutations <ul><li>MUTATIONS  are changes in the genetic makeup of a cell. </li></ul>
<ul><li>POINT MUTATIONS  - chemical changes in just one nucleotide in a single gene. e.g. gene in gamete with point mutati...
Types of Mutations <ul><li>SUBSTITUTIONS : base-pair is replaced by another pair of nucleotides. Net result is a MISSENSE ...
<ul><li>May not be a problem unless it is a termination codon (NONSENSE MUTATION). </li></ul>
Types of Mutations <ul><li>INSERTIONS & DELETIONS :  addition or loss of a nucleotide pairs in a gene. This more disastero...
<ul><li>Unless three nucleotides are added or deleted, or the mutation is near the end of the gene, the protein is likely ...
Molecular Basis of Sickle-Cell Disease: A Point Mutation
Categories & Consequences of Point Mutations (Fig. 17.22)
Mutagens <ul><li>MUTAGENS  - physical or chemical agents that interact with DNA to cause mutations (e.g. x-rays, UV light)...
<ul><li>AMES TEST  - for mutagenic strength of chemicals (pesticides, drugs for mutagenic & cancer-causing potential) see ...
See Figure 17.23 Transcription & Translation
Upcoming SlideShare
Loading in …5
×

Chapter 17

2,187 views
2,109 views

Published on

2 Comments
1 Like
Statistics
Notes
No Downloads
Views
Total views
2,187
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
81
Comments
2
Likes
1
Embeds 0
No embeds

No notes for slide

Chapter 17

  1. 1. Chapter 16: Review Molecular Basis of Inheritance <ul><li>Search for genetic material led to DNA </li></ul><ul><li>Discovery- DNA double helix </li></ul><ul><li>DNA replication: Basics </li></ul><ul><li>DNA repair </li></ul>
  2. 2. Chapter 17: From Gene to Protein <ul><li>Study of metabolic defects provided evidence that genes specify proteins </li></ul><ul><li>Transcription & translation are main processes linking gene to protein. </li></ul><ul><li>Genetic code : nucleotide triplets specify amino acids </li></ul>
  3. 3. <ul><li>Transcription is the DNA-directed synthesis of RNA </li></ul><ul><li>Signal peptides target some eukaryotic polypeptides to specific destinations in the cell </li></ul><ul><li>RNA plays multiple roles in the cell </li></ul><ul><li>Compare protein synthesis in prokaryotes & eukaryotes . </li></ul>
  4. 4. <ul><li>A point mutation can affect the function of a protein </li></ul><ul><li>Ask again, what is a gene? </li></ul>
  5. 5. Study of Metabolic Defects Provided Evidence that Genes Specify Proteins <ul><li>Archibald Garrod (1909) proposed relationship between genes & proteins (alkaptonuria, dark urine) </li></ul><ul><li>George Beadle & Edward Tatum (1930s) demonstrated the relationship between genes & enzymes while studying a bread mold with mutants. </li></ul>
  6. 6. How Do Genes Control Metabolism <ul><li>Beadle & Tatum </li></ul><ul><li>Red bread mold (maybe you know it) </li></ul><ul><li>Wild-type strain has minimal requirements. </li></ul><ul><li>Multi-step pathway to synthesize the amino acid arginine from a precursor </li></ul><ul><li>Three classes of mutants unable to metabolize arginine. </li></ul>
  7. 7. Neurospora - Red Bread Mold
  8. 8. <ul><li>They concluded that each mutant was defective in a single gene coding for one enzyme. </li></ul><ul><li>This lead to the one gene-one enzyme hypothesis: the function of a gene is to dictate the production of a specific enzyme. </li></ul>
  9. 9. Modified Idea <ul><li>This idea was modified to be one gene-one polypeptide hypothesis because: not all proteins are enzymes (keratin, insulin). </li></ul><ul><li>Many proteins are made of several polypeptides (hemoglobin, 2 chains). </li></ul>
  10. 10. Transcription & Translation: Two Main Steps from Gene to Protein <ul><li>Genes are the instructions for making specific proteins, but a gene does not build a protein directly. </li></ul><ul><li>The bridge between genetic information and protein synthesis is RNA, ribonucleic acid (Chap. 5). </li></ul>
  11. 11. DNA & RNA: Both Polymers <ul><li>Both RNA & DNA are nucleotide polymers with two main differences: deoxyribose of DNA has one less hydroxyl group than ribose (sugar); the other difference is the nitrogenous base- thymine (T) is unique to DNA & uracil (U) unique to RNA. </li></ul>
  12. 12. DNA & RNA Structural Differences
  13. 13. <ul><li>Flow of information - gene to protein, is described in linguistic terms because both nucleic acids and proteins have specific sequences of monomers, much as specific sequences of letters communicate information in the written word. </li></ul>
  14. 14. <ul><li>DNA/RNA - monomers are the four types of nucleotides (nitrogenous bases differ) that are 100’s or 1000’s of nucleotides long, each gene having a specific base sequence. </li></ul>
  15. 15. <ul><li>A protein has monomers in a particular linear order, but the monomers are......? </li></ul>
  16. 16. Amino Acids <ul><li>Amino acids..20 of them. </li></ul><ul><li>Thus, nucleic acids & proteins contain information written in two different chemical languages.... </li></ul>
  17. 17. <ul><li>Getting from one to the other requires two major steps: Transcription and Translation </li></ul>
  18. 18. Transcription <ul><li>Transcription is the synthesis of RNA under the direction of DNA (template...recall replication). Both nucleic acids use the same monomeric language, the information just has to be transcribed (copied) from one molecule to another. </li></ul>
  19. 19. <ul><li>The RNA molecule made according to the DNA template is a transcript of the gene’s protein-building instructions. </li></ul>
  20. 20. <ul><li>This RNA is called mRNA (messenger RNA) , which functions as a genetic message from DNA to the protein-synthesizing machinery. </li></ul>
  21. 21. <ul><li>Translation is the actual synthesis of a polypeptide, which occurs under the direction of mRNA. </li></ul>
  22. 22. <ul><li>There is a change in language from the base sequence of an mRNA into the amino acid sequence of a polypeptide. </li></ul>
  23. 23. <ul><li>Ribosomes are the sites of translation , which are made of numerous enzymes & other agents that facilitate the orderly linking of amino acids. </li></ul>
  24. 24. Prokaryote/Eukaryote Difference? <ul><li>Bacteria lack a nuclei, so DNA is not segregated from ribosomes, etc. </li></ul><ul><li>Thus, transcription & translation are coupled, with ribosomes attaching to the leading end of an mRNA molecule while transcription is still ongoing. (Fig. 17.2, CD). </li></ul>
  25. 25. Prokaryotic Cell Immediate Translation No Nucleus
  26. 26. Eukaryotic Cell Nucleus RNA Processing
  27. 27. <ul><li>DNA RNA Protein </li></ul>
  28. 28. Genetic Code: Nucleotide Triplets Specify Amino Acids <ul><li>Only four nucleotides code for 20 amino acids. </li></ul>
  29. 29. Codon <ul><li>Three nucleotide “words” are called codons. </li></ul><ul><li>Codon =three-nucleotide sequence in mRNA that specifies which amino acid will be added to a growing polypeptide or that signals termination. </li></ul><ul><li>Codon is basic unit of genetic code. </li></ul>
  30. 30. Recall....... <ul><li>Genes are not directly translated into amino acids, but are first transcribed as codons into mRNA. </li></ul><ul><li>Only one strand is transcribed, the other non-template strand serves as a parental strand for making a new template when DNA replicates. </li></ul>
  31. 31. <ul><li>An mRNA is complementary to the DNA template from which it is transcribed, for example, the DNA sequence CCG is the codon for glycine, the complementary mRNA transcript is GGC. Uracil substitutes for thymine & pairs with adenine (Fig. 17.3). </li></ul>
  32. 32. Triplet Code DNA mRNA Amino Acid
  33. 33. Fig. 17.4 Triplet code. <ul><li>Each mRNA codon specifies which one of the 20 amino acids will be incorporated into a corresponding position in a polypeptide. </li></ul><ul><li>The number of nucleotides making up a genetic message is 3 times the number of amino acids. </li></ul>
  34. 34. Cracking the Genetic Code <ul><li>By the mid-1960s all 64 codons were known. Figure 17.4 is the dictionary of the genetic code. </li></ul>
  35. 35. GENETIC CODE AUG Met. = Start Stop= UAA UAG UGA
  36. 36. Factoid <ul><li>AUG that codes for methionine (Met, start signal or initiation codon) is sometimes removed subsequently. </li></ul>
  37. 37. <ul><li>There is redundancy in the code....several codons for one amino acid, but there is no ambiguity (same codon for two amino acids). Codons for the same amino acid may differ only in the third base of the triplet. </li></ul>
  38. 38. Reading Frame <ul><li>Reading frame = correct grouping of adjacent nucleotide triplets into codons that are in the correct sequence on mRNA.… nonoverlapping three-letter words. </li></ul>
  39. 39. Reading frame <ul><li>THE BIG RED CAT ATE THE BIG BAD FAT RAT. </li></ul><ul><li>HEB IGR EDC ATA TET HEB IGB ADF ATR AT- </li></ul>
  40. 40. <ul><li>My codon is A D D. </li></ul><ul><ul><li>A ttention </li></ul></ul><ul><ul><li>D eficit </li></ul></ul><ul><ul><li>D isorder </li></ul></ul><ul><li>What is your codon? </li></ul>
  41. 41. The Genetic Code <ul><li>The genetic code is nearly universal - a language that is shared across all of life meaning it must have been operating very early in the history of life. </li></ul>
  42. 42. Transcription Up Close Transcription is the DNA-Directed Synthesis of RNA <ul><li>RNA polymerases pry apart the two DNA strands & hook together the RNA nucleotides as they base pair along the template beginning at the 3’ end. </li></ul>
  43. 43. <ul><li>DNA that is transcribed into an RNA molecule is the TRANSCRIPTION UNIT . </li></ul>
  44. 44. Transcription Up Close <ul><li>Prokaryotes have one RNA polymerase. Eukaryotes have three. </li></ul><ul><li>mRNA synthesis-RNA polymerase II </li></ul><ul><li>Transcription steps : 1) polymerase binding & initiation 2) elongation 3) termination </li></ul>
  45. 45. RNA Polymerase Binding & Initiation <ul><li>RNA polymerases bind to DNA regions called PROMOTORS . </li></ul>
  46. 46. <ul><li>Promoter = initiation site + dozens of nucleotides “upstream” from initiation site. e.g. TATA box (eukaryotes) are 25 bases upstream. </li></ul>
  47. 47. <ul><li>TRANSCRIPTION FACTORS - aid polymerases in finding promotor regions on DNA (sometimes attach before polymerase can bind). </li></ul>
  48. 48. Elongation <ul><li>RNA polymerase II untwists DNA one turn (helix) at a time exposing 10 bases for pairing of RNA nucleotides at the 3’ end. </li></ul>
  49. 49. <ul><li>mRNA peels away as the noncoding strand reforms the double helix. </li></ul>
  50. 50. <ul><li>A single gene can be transcribed simultaneously by several polymerase IIs so it can produce proteins faster (more copies of mRNA). </li></ul>
  51. 51. Termination <ul><li>RNA polymerase transcribes until termination site is reached (AAAAAA in eukaryotes). </li></ul><ul><li>Play CD #2 </li></ul>
  52. 52. Figure 17.6
  53. 53. Figure 17.7 Initiation of Transcription at a Eukaryotic Promoter
  54. 54. Eukaryotic Cell Modify RNA after Transcription <ul><li>Alternation of mRNA Ends </li></ul><ul><li>Split Genes and RNA Splicing </li></ul><ul><li>Ribozymes </li></ul>
  55. 55. RNA Processing : Both ends (5’ & 3’) are modified, then cut apart & spiced together again <ul><li>Alteration of mRNA ends - in the nucleus - 5’ Cap protects mRNA & is an “attach here” signal for small ribosomes. </li></ul>
  56. 56. <ul><li>- 3’ Poly-A tail (several hundred adenines) for protection & transport from nucleus to cytoplasm. </li></ul>
  57. 57. RNA Processing: Add Cap & Tail 5’Cap 3’Tail
  58. 58. RNA Processing : <ul><li>RNA splicing - Average DNA molecule is 8000 bases, RNA in nucleus is same length, but 1200 nucleotides to code for protein of 400 amino acids. </li></ul>
  59. 59. <ul><li>What happened to the 6,800 nucleotides between the nucleus and cytoplasm....? </li></ul>
  60. 60. RNA Processing : <ul><li>INTRONS - intervening noncoding segments of DNA are transcribed then removed. </li></ul>
  61. 61. <ul><li>EXONS - are coding regions that are express eventually (translated into proteins). </li></ul><ul><li>RNA splicing occurs for tRNA & rRNA & mRNA. (see Figure 17.9). </li></ul>
  62. 62. RNA Processing: Splicing Transcription Introns Excised Exons Spliced
  63. 63. Play CD
  64. 64. Synthesis of Protein Translation Up Close (p. 304) <ul><li>In the Process of Translation a cell interprets a genetic message & builds a protein. </li></ul><ul><li>The message is a series of codons along the mRNA molecule </li></ul><ul><li>The interpreter is another type of RNA - TRANSFER RNA (tRNA). </li></ul>
  65. 65. TRANSFER RNA <ul><li>tRNA transfers amino acids from the cytoplasm’s amino acid pool to the ribosome . </li></ul><ul><li>Cell keep the pool stocked with 20 amino acids it makes or takes up from the surrounding solution. </li></ul>
  66. 66. <ul><li>Some 45 different tRNA molecules associate with particular mRNA codons that code for amino acids. </li></ul>
  67. 67. Translation Up Close <ul><li>On one end is a tRNA’s particular amino acid, on the other end is a base triplet called an ANTICODON </li></ul><ul><li>The anticodon binds according to the base-pairing rules to a mRNA codon. </li></ul><ul><li>Ribosomal enzymes join amino acids into a chain. </li></ul>
  68. 68. Transfer RNA <ul><li>tRNAs are transcribed in the nucleus from DNA templates (nucleus) then travel to cytoplasm for translation where they are used repeatedly. </li></ul>
  69. 69. <ul><li>Some tRNAs have anticodons that recognize two or more codons. The third base pairings (between anticodon & mRNA) are not as strict. </li></ul>
  70. 70. <ul><li>This relaxation of base-pairing rules is called WOBBLE . Explains synonymous codons for certain amino acids. </li></ul>
  71. 71. <ul><li>See Figure 17.13 for aminoacyl-tRNA synthase joining a tRNA to an amino acid...... </li></ul>
  72. 72. Ribosomes <ul><li>Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis. </li></ul><ul><li>Ribosomal unit = proteins (large & small subunit) + ribosomal RNA (rRNA) </li></ul>
  73. 73. Building a Polypeptide <ul><li>Initiation>Elongation> Termination </li></ul>
  74. 74. Building a Polypeptide <ul><li>Initiation : mRNA + tRNA (with amino acid) + two ribosomal subunits + GTP (energy). </li></ul>
  75. 75. Initiation of Translation
  76. 76. Building a Polypeptide <ul><li>Elongation : Codon recognition (+GTP) > Peptide bond formation (peptidyl transferase) & release of amino acid from tRNA </li></ul>
  77. 77. Elongation of Translation Codon Recognition Peptide Bond Formation
  78. 78. Building a Polypeptide <ul><li>Translocation : tRNA dissociates from ribosome....mRNA & ribosome move in unison (ratchet-like) . </li></ul>
  79. 79. Elongation of Translation Translocation A Site P Site
  80. 80. Building a Polypeptide <ul><li>Termination : Elongation until TERMINATION CODON reached (UAA, UAG, UGA - not amino acid codons) Release factor hydrolyzes the completed polypeptide from the tRNA, freeing the polypeptide from the ribosome. </li></ul><ul><li>See Figures 17.14 - 17 </li></ul>
  81. 81. Termination of Translation Free Polypeptide Termination Codon Ribosome Dissociation
  82. 82. Play CD
  83. 83. Building a Polypeptide <ul><li>POLYRIBOSOMES - more than one ribosome translating on same mRNA molecule (Figure 17.18 in book). </li></ul>
  84. 84. Signal Peptides <ul><li>Free (cytosol) & bound (to endoplasmic reticulum) ribosomes - Free - proteins in cytosol Bound - membrane proteins & proteins to be secreted. </li></ul>
  85. 85. <ul><li>SIGNAL SEQUENCE - on peptide enables ribosome to attach to receptor site on ER membrane (signal seq. is eventually removed). </li></ul>
  86. 86. Signal Mechanism for Targeting Proteins Signal Recognition Particle Signal Sequence Receptor Site Endoplasmic Reticulum
  87. 87. Types of RNA in a Eukaryote See Table 17.1 <ul><li>Messenger RNA </li></ul><ul><li>Transfer RNA </li></ul><ul><li>Ribosomal RNA </li></ul><ul><li>Primary transcript </li></ul><ul><li>Small nuclear RNA </li></ul><ul><li>Signal recognition particle </li></ul>
  88. 88. Mutations <ul><li>MUTATIONS are changes in the genetic makeup of a cell. </li></ul>
  89. 89. <ul><li>POINT MUTATIONS - chemical changes in just one nucleotide in a single gene. e.g. gene in gamete with point mutation may be passed on to next generation (genetic disorder) </li></ul>
  90. 90. Types of Mutations <ul><li>SUBSTITUTIONS : base-pair is replaced by another pair of nucleotides. Net result is a MISSENSE mutation that still codes for an amino acid. </li></ul>
  91. 91. <ul><li>May not be a problem unless it is a termination codon (NONSENSE MUTATION). </li></ul>
  92. 92. Types of Mutations <ul><li>INSERTIONS & DELETIONS : addition or loss of a nucleotide pairs in a gene. This more disasterous as may throw off reading frame causing a FRAMESHIFT MUTATION . </li></ul>
  93. 93. <ul><li>Unless three nucleotides are added or deleted, or the mutation is near the end of the gene, the protein is likely to be nonfunctional. </li></ul>
  94. 94. Molecular Basis of Sickle-Cell Disease: A Point Mutation
  95. 95. Categories & Consequences of Point Mutations (Fig. 17.22)
  96. 96. Mutagens <ul><li>MUTAGENS - physical or chemical agents that interact with DNA to cause mutations (e.g. x-rays, UV light). </li></ul>
  97. 97. <ul><li>AMES TEST - for mutagenic strength of chemicals (pesticides, drugs for mutagenic & cancer-causing potential) see text. </li></ul>
  98. 98. See Figure 17.23 Transcription & Translation

×