Microbial Genetics <ul><li>Dr. Gary Andersen, 913-279-2211 </li></ul><ul><li>Some slides used with permission from Curtis ...
Basic Units of Genetics <ul><li>Genomes – the total of the genetic material in a cell.  </li></ul><ul><li>Gene -  The unit...
A Big Question to Struggle With <ul><li>Which is more important… nature or nurture?  Genetics or the environment?  In dete...
Nucleic Acids <ul><li>I.  Nucleic acids  are located in the nucleoid of bacteria, and the nucleus of eukaryotes.  There ar...
DNA <ul><li>CHARACTERISTICS OF DNA </li></ul><ul><li>DNA (deoxyribonucleic acid)  is made of subunits called  nucleotides ...
Significance of DNA Structure <ul><li>Maintains the code with high degree of fidelity. (double strand assures accurate rep...
1. COMPONENT 1 - Phosphate <ul><li>Phosphate group - Phosphate functions as a structural part of nucleic acids. </li></ul>
2. COMPONENT – Ribose Sugar <ul><li>2, DEOXYRIBONUCLEIC ACID   </li></ul><ul><li>Ribose - A five carbon sugar that functio...
3. COMPONENT – Nitrogen Bases <ul><li>NITROGEN CONTAINING BASES </li></ul><ul><li>Function:  express genetic information. ...
Nucleotide Base Composed of one Nitrogen base, one Deoxyribose, and one Phosphate group Phosphate Deoxyribose Adenine (Nit...
4 Nucleotides A G T C
DNA Structure
DNA Structure <ul><li>4. DNA is a  double helix  (there are 2 strands of DNA) which are intertwined with 5 base pairs per ...
DNA Bonds
3-D Image of DNA
B. RNA <ul><li>RIBONUCLEIC ACID </li></ul><ul><li>Similar to DNA except: </li></ul><ul><li>1.  RNA is  single stranded </l...
 
C. FUNCTIONS OF RNA <ul><li>1.  rRNA  (ribosomal) - comprises the ribosome (site of protein synthesis). (60% of a ribosome...
THE CENTRAL DOGMA OF BIOLOGY  “Francis Crick – 1956” <ul><li>There are  3 parts  to the flow of  information in all cells....
Central Dogma of Biology
DNA REPLICATION <ul><li>1.  Where 2 parental strands of DNA are copied into 2 daughter strands.  Rate = 1,000 nucs per sec...
As the two replication forks meet, the two new chromosomes separate—each containing one new and one old strand
Replication bonding
Replication Fork
1.  EVENTS IN DNA REPLICATION <ul><li>DNA unwinds using the enzyme  DNA Helicase   </li></ul><ul><li>SSBP  holds the 2 str...
DNA REPLICTION CONTINUED <ul><li>Polymerization requires  DNA Polymerase  (POL III) which is an enzyme that synthesizes 2 ...
DNA Replication Enzymes at Work
Steps in Replication
Replication of DNA cont’d <ul><li>http://www.ncc.gmu.edu/dna/repanim.htm </li></ul>
THE CENTRAL DOGMA OF BIOLOGY <ul><li>There are  3 parts  to the flow of  information in all cells. </li></ul><ul><li>Trans...
B.  TRANSCRIPTION <ul><li>2nd part of the central dogma of biology </li></ul><ul><li>1st step in gene expression (i.e.prot...
TRANSCRIPTION CONTINUED <ul><li>5.  RNA polymerase is the enzyme responsible for making mRNA </li></ul>
Transcription continued <ul><li>7.  Example: </li></ul><ul><li>DNA  A  T  G  C  C  G  </li></ul><ul><li>DNA  T  A  C  G  G...
Animation of Transcription <ul><li>http://www.ncc.gmu.edu/dna/mRNAanim.htm </li></ul>
C.  TRANSLATION <ul><li>Translation is the 3rd part of the central dogma of biology (2nd step in gene expression or protei...
Translation Graphic
TRANSLATION CONTINUED <ul><li>tRNA   STRUCTURE </li></ul><ul><li>tRNA utilizes the information in mRNA to determine the se...
Transfer RNA Structure
TRANSLATION CONTINUED <ul><li>The mechanics of translation   </li></ul><ul><li>Initiation ; mRNA bumps into the small subu...
TRANSLATION CONTINUED <ul><li>b.  Elongation – The second tRNA binds to the second code word on mRNA.  A peptide bond form...
TRANSLATION CONTINUED <ul><ul><li>C.  In termination, one of three possible stop codons is reached.  The last tRNA falls a...
d.  The Genetic Code <ul><li>61 sense codons for 20 amino  acids </li></ul><ul><li>3  nonsense (or stop codons) </li></ul>...
The Genetic Code
Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Steps in Protein Synthesis
Protein Synthesis
Translation - Animation <ul><li>http://www. ncc . gmu . edu/dna/ANIMPROT . htm </li></ul>Translation Animation -  http://w...
<ul><li>Translation Blockers </li></ul><ul><ul><li>Streptomycin – (SM) blocks assembly of the ribosome during initiation. ...
Gene Regulation <ul><li>How can genes be turned off and on? </li></ul><ul><li>Examples from E. coli </li></ul><ul><ul><li>...
Induction - Lac operon
Repression - Trp operon
III.  5 Ways of Creating Genetic Diversity in Bacteria <ul><ul><li>A.  Mutations </li></ul></ul><ul><ul><li>B.  Transforma...
A.  Mutations <ul><li>1.  Changes in the nucleotide sequence  usually due to an error in DNA  replication.  These occur na...
Results of Mutations <ul><li>2. Most mutations are  neutral  - they have no effect on the polypeptide.  Some mutations res...
Types of Mutations <ul><li>3.  Point mutations  - a one base change in DNA.  There are 3 types: </li></ul><ul><ul><li>a . ...
<ul><ul><li>b.   missense mutations  - single base substitution in 1st or 2nd base nucleotide position.  This results in a...
<ul><ul><li>a.   Chemical mutagens  -  (used in research to  study mutagenesis).  There are 3 kinds of  chemical mutagens....
<ul><ul><li>b.  Physical mutagens : </li></ul></ul><ul><ul><ul><li>1.  nonionizing radiation  -  Causes the formation of T...
B.  TRANSFORMATION <ul><li>The passage of homologous DNA from a dead donor cell to a living recipient cell.  Occurs in  St...
Transformation Graphic
Griffith’s Transformation Experiment
C.  CONJUGATION <ul><li>1.  A “mating” process between a donor  F+  (bacteria with fertility factor =plasmid)   and an F- ...
Conjugation continued <ul><li>“ Normal - Sex” plasmid transfer  (usually ~20 of 100 genes). </li></ul><ul><ul><li>a.  Requ...
<ul><li>6.  Hfr ( High Frequency Recombination ) </li></ul><ul><li>a.  Hfr- bacterial plasmid integrates into the  chromos...
 
D.  TRANSPOSITION  p 285 <ul><li>Transposons  (jumping genes) are big  chunks of DNA that randomly excise and relocate on ...
E.  TRANSDUCTION <ul><li>the transfer of genetic material from donor bacteria to recipient bacteria via a  transducing age...
 
<ul><ul><li>2.  Generalized transduction :  Starts with the  LYTIC CYCLE  where a  T- even   phage   (Fig. 8.5 pg 210) inf...
Generalized Transduction
Generalized Transduction
Specialized Transduction <ul><li>3.   Specialized transduction   </li></ul><ul><li>Lambda  phage infects  E.coli .  The ph...
Specialized Transduction Cont. <ul><li>The gal transducing phage  (lambda)  makes ~ 2,000 copies of itself with the gal ge...
Specialized Transduction Graphic
Comparison of Bacteriophage <ul><li>3.  Comparison of bacteriophage transduction  in  E.coli . </li></ul><ul><ul><ul><ul><...
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Lecture 2a Microbial Genetics.ppt

  1. 1. Microbial Genetics <ul><li>Dr. Gary Andersen, 913-279-2211 </li></ul><ul><li>Some slides used with permission from Curtis Smith, KCKCC </li></ul><ul><li>Reference: Chapter 7,8 from (Black, J., 2005) </li></ul>
  2. 2. Basic Units of Genetics <ul><li>Genomes – the total of the genetic material in a cell. </li></ul><ul><li>Gene - The unit of heredity for a given genetic trait. The site on a DNA molecule that carries the code for a certain cell function. </li></ul><ul><li>Viruses – 4 or 5 genes, E. coli – 4228 genes, Human ~ 31,000 genes. </li></ul>
  3. 3. A Big Question to Struggle With <ul><li>Which is more important… nature or nurture? Genetics or the environment? In determining the characteristics and behavior of an organism? </li></ul>
  4. 4. Nucleic Acids <ul><li>I. Nucleic acids are located in the nucleoid of bacteria, and the nucleus of eukaryotes. There are 2 kinds of nucleic acids: RNA & DNA. </li></ul>Ruptured E. coli cell showing DNA
  5. 5. DNA <ul><li>CHARACTERISTICS OF DNA </li></ul><ul><li>DNA (deoxyribonucleic acid) is made of subunits called nucleotides . Nucleotides are made of 3 components. These 3 components are linked together with a covalent bond. </li></ul><ul><li>E. Coli = 4.6 million nucleotide pairs (~1mm) </li></ul><ul><li>Corn = 2.5 billion nucleotide pairs </li></ul><ul><li>Human = 3 billion nucleotide pairs (2nm wide by 2 meters long) </li></ul>
  6. 6. Significance of DNA Structure <ul><li>Maintains the code with high degree of fidelity. (double strand assures accurate replication) </li></ul><ul><li>Provides a method for introducing a high degree of variety. (unlimited variety of sequences possible) </li></ul>
  7. 7. 1. COMPONENT 1 - Phosphate <ul><li>Phosphate group - Phosphate functions as a structural part of nucleic acids. </li></ul>
  8. 8. 2. COMPONENT – Ribose Sugar <ul><li>2, DEOXYRIBONUCLEIC ACID </li></ul><ul><li>Ribose - A five carbon sugar that functions as part of the DNA backbone (ie. structural). “2, Deoxy” means without oxygen on the number 2 carbon atom. </li></ul>
  9. 9. 3. COMPONENT – Nitrogen Bases <ul><li>NITROGEN CONTAINING BASES </li></ul><ul><li>Function: express genetic information. </li></ul><ul><li>composition : </li></ul><ul><li>2 PURINES: ADENINE (A) GUANINE ( G) </li></ul><ul><li>double ring structures </li></ul><ul><li>2 PYRIMIDINES: THYMINE(T) CYTOSINE(C) </li></ul><ul><li>single ring structures </li></ul>
  10. 10. Nucleotide Base Composed of one Nitrogen base, one Deoxyribose, and one Phosphate group Phosphate Deoxyribose Adenine (Nitrogen base)
  11. 11. 4 Nucleotides A G T C
  12. 12. DNA Structure
  13. 13. DNA Structure <ul><li>4. DNA is a double helix (there are 2 strands of DNA) which are intertwined with 5 base pairs per turn. </li></ul><ul><li>5. DNA has complimentarity </li></ul><ul><li>that is A always bonds with T </li></ul><ul><li>and G always with C </li></ul><ul><li>6. DNA is always antiparallel . The 2 strands of DNA are always oriented in opposite directions. ( 5’ PO 3 end – 3’ OH end) </li></ul><ul><li>http://www.umass.edu/microbio/chime/dna/dna53.htm </li></ul>
  14. 14. DNA Bonds
  15. 15. 3-D Image of DNA
  16. 16. B. RNA <ul><li>RIBONUCLEIC ACID </li></ul><ul><li>Similar to DNA except: </li></ul><ul><li>1. RNA is single stranded </li></ul><ul><li>2. RNA has a ribose sugar instead of deoxyribose. (Oxygen on #2 C). </li></ul><ul><li>3. RNA has URACIL ( u ) instead of thymine </li></ul><ul><li>4. RNA is always shorter than DNA, ~ 1,000 nucleotides in length </li></ul>
  17. 18. C. FUNCTIONS OF RNA <ul><li>1. rRNA (ribosomal) - comprises the ribosome (site of protein synthesis). (60% of a ribosome is made of RNA, the rest is protein). </li></ul><ul><li>2. tRNA (transfer) carries amino acids to the ribosome during protein synthesis. Also known as the “ ANTICODON ” </li></ul><ul><li>3. mRNA (messenger) - a complimentary strand of RNA equal in size to 1 gene (normally ~1,000 nucleotides). “ CODON ” - coded info from DNA (bound for the ribosome) </li></ul>
  18. 19. THE CENTRAL DOGMA OF BIOLOGY “Francis Crick – 1956” <ul><li>There are 3 parts to the flow of information in all cells. </li></ul><ul><li>Transcription Translation </li></ul><ul><li>DNA -------------  mRNA-----  protein </li></ul><ul><li>Replication </li></ul>
  19. 20. Central Dogma of Biology
  20. 21. DNA REPLICATION <ul><li>1. Where 2 parental strands of DNA are copied into 2 daughter strands. Rate = 1,000 nucs per seconds without error. This leads to binary fission in bacteria. </li></ul><ul><li>Cell Division) = 2 daughter cells </li></ul><ul><li>2. Each cell receives 1 parental strand and 1 daughter strand. ( semiconservative replication ) </li></ul>GA sp 08
  21. 22. As the two replication forks meet, the two new chromosomes separate—each containing one new and one old strand
  22. 23. Replication bonding
  23. 24. Replication Fork
  24. 25. 1. EVENTS IN DNA REPLICATION <ul><li>DNA unwinds using the enzyme DNA Helicase </li></ul><ul><li>SSBP holds the 2 strands apart (single strand binding proteins) </li></ul><ul><li>Note: 2 replication forks . DNA replication is considered bi-directional replication . </li></ul>
  25. 26. DNA REPLICTION CONTINUED <ul><li>Polymerization requires DNA Polymerase (POL III) which is an enzyme that synthesizes 2 nucleotide strands (daughter strands) from 2 parental (templates) strands. </li></ul><ul><li>DNA exonuclease (POL I) removes any mistaken base pairs. </li></ul><ul><li>DNA ligase seals any gaps and joins the 2 strands together . </li></ul>
  26. 27. DNA Replication Enzymes at Work
  27. 28. Steps in Replication
  28. 29. Replication of DNA cont’d <ul><li>http://www.ncc.gmu.edu/dna/repanim.htm </li></ul>
  29. 30. THE CENTRAL DOGMA OF BIOLOGY <ul><li>There are 3 parts to the flow of information in all cells. </li></ul><ul><li>Transcription Translation </li></ul><ul><li>DNA -------------  mRNA-----  protein </li></ul><ul><li>Replication </li></ul>
  30. 31. B. TRANSCRIPTION <ul><li>2nd part of the central dogma of biology </li></ul><ul><li>1st step in gene expression (i.e.protein synthesis). </li></ul><ul><li>The cells genetic plan contained in DNA is transcribed into a complimentary base sequence called messenger RNA (mRNA). </li></ul><ul><li>The region of DNA that produces or serves as a template for mRNA is called a gene . A gene normally consists of around 1,000 base pairs. It is the smallest segment of DNA that codes for mRNA. </li></ul>
  31. 32. TRANSCRIPTION CONTINUED <ul><li>5. RNA polymerase is the enzyme responsible for making mRNA </li></ul>
  32. 33. Transcription continued <ul><li>7. Example: </li></ul><ul><li>DNA A T G C C G </li></ul><ul><li>DNA T A C G G C </li></ul><ul><li>mRNA A U G C C G </li></ul><ul><li>8. mRNA is a blueprint of DNA or a transcript or code. </li></ul><ul><li>9. One code word consists of three letters. </li></ul>
  33. 34. Animation of Transcription <ul><li>http://www.ncc.gmu.edu/dna/mRNAanim.htm </li></ul>
  34. 35. C. TRANSLATION <ul><li>Translation is the 3rd part of the central dogma of biology (2nd step in gene expression or protein synthesis). </li></ul><ul><li>After transcription, the coded information in mRNA is translated into an enzyme (protein). </li></ul><ul><li>This process takes place on the ribosome . Note that the ribosome is made of rRNA and protein. </li></ul>
  35. 36. Translation Graphic
  36. 37. TRANSLATION CONTINUED <ul><li>tRNA STRUCTURE </li></ul><ul><li>tRNA utilizes the information in mRNA to determine the sequence of amino acids in a protein. tRNA has a cloverleaf shape. The amino acid end binds one specific amino acid in the cytoplasm. The anticodon end pairs with the codon on mRNA. </li></ul>
  37. 38. Transfer RNA Structure
  38. 39. TRANSLATION CONTINUED <ul><li>The mechanics of translation </li></ul><ul><li>Initiation ; mRNA bumps into the small subunit and triggers the two ribosomal subunits to bind together. The first tRNA anticodon (UAC) carrying the amino acid methionine hydrogen bonds with the codon AUG on mRNA. </li></ul>
  39. 40. TRANSLATION CONTINUED <ul><li>b. Elongation – The second tRNA binds to the second code word on mRNA. A peptide bond forms between the two amino acids. The first tRNA leaves, and the enzyme translocase moves the ribosome down one code word of mRNA at a time. This repeats ~ 300X. </li></ul>
  40. 41. TRANSLATION CONTINUED <ul><ul><li>C. In termination, one of three possible stop codons is reached. The last tRNA falls away and the two ribosomal subunits fall apart. </li></ul></ul>
  41. 42. d. The Genetic Code <ul><li>61 sense codons for 20 amino acids </li></ul><ul><li>3 nonsense (or stop codons) </li></ul><ul><li>total codons </li></ul><ul><li>Pg 180 (Black, J., 2005) </li></ul>
  42. 43. The Genetic Code
  43. 44. Steps in Protein Synthesis
  44. 45. Steps in Protein Synthesis
  45. 46. Steps in Protein Synthesis
  46. 47. Steps in Protein Synthesis
  47. 48. Steps in Protein Synthesis
  48. 49. Protein Synthesis
  49. 50. Translation - Animation <ul><li>http://www. ncc . gmu . edu/dna/ANIMPROT . htm </li></ul>Translation Animation - http://www. wehi . edu . au/wehi-tv/dna/movies/Translation . mov . gz
  50. 51. <ul><li>Translation Blockers </li></ul><ul><ul><li>Streptomycin – (SM) blocks assembly of the ribosome during initiation. </li></ul></ul><ul><ul><li>Chloroamphenicol – (CA) blocks peptide bond formation during elongation. </li></ul></ul><ul><ul><li>Tetracycline – TC – blocks the 2 nd site on the ribosome during elongation. </li></ul></ul><ul><ul><li>Erythromycin EM – blocks translocase during elongation. </li></ul></ul>GA sp07
  51. 52. Gene Regulation <ul><li>How can genes be turned off and on? </li></ul><ul><li>Examples from E. coli </li></ul><ul><ul><li>Inducer – example is lactose (lac operon), pg 187 of (Black, J., 2005) </li></ul></ul><ul><ul><li>Repressor – argenine (arg operon), pg 187-188 of (Black, J., 2005) </li></ul></ul>
  52. 53. Induction - Lac operon
  53. 54. Repression - Trp operon
  54. 55. III. 5 Ways of Creating Genetic Diversity in Bacteria <ul><ul><li>A. Mutations </li></ul></ul><ul><ul><li>B. Transformation </li></ul></ul><ul><ul><li>C. Conjugation </li></ul></ul><ul><ul><li>D. Transposition </li></ul></ul><ul><ul><li>E. Transduction </li></ul></ul>
  55. 56. A. Mutations <ul><li>1. Changes in the nucleotide sequence usually due to an error in DNA replication. These occur naturally at low levels (also known as spontaneous mutations ); or by the effects of chemical agents called mutagens; or by physical agents like radiation. </li></ul>
  56. 57. Results of Mutations <ul><li>2. Most mutations are neutral - they have no effect on the polypeptide. Some mutations result in a less active product; Less often an inactive product; Very few mutations are beneficial. However , these would be passed on ! </li></ul>
  57. 58. Types of Mutations <ul><li>3. Point mutations - a one base change in DNA. There are 3 types: </li></ul><ul><ul><li>a . silent mutations - single base substitution in the 3rd base nucleotide position of a codon. This results in NO change in amino acid . Note that the first 2 letters of the genetic code are the most critical . </li></ul></ul>
  58. 59. <ul><ul><li>b. missense mutations - single base substitution in 1st or 2nd base nucleotide position. This results in a changed amino acid . A change in one amino acid usually will have little effect depending on where in the polypeptide it occurs. </li></ul></ul><ul><ul><li>nonsense mutations - single base substitutions that yield a stop codon . Note: there are 3 nonsense codons in the genetic code = NO PROTEIN </li></ul></ul><ul><li>4. Frame Shift Mutations - the addition or deletion of 1 or more bases. These are due to powerful mutagens; chemical or physical. </li></ul>
  59. 60. <ul><ul><li>a. Chemical mutagens - (used in research to study mutagenesis). There are 3 kinds of chemical mutagens. </li></ul></ul><ul><ul><li>1. alkylating agents . Adds alkyl group, C n H (2n+1) Ex. formalin, nitrogen, mustard, and ethylene oxide (reacts with G changing it to bind with T). </li></ul></ul><ul><ul><li>2. base analogs . Mimics a nitrogen base. Ex. AZT is a modified sugar that substitutes for T. Ex. 5 - bromouracil binds with A or G. </li></ul></ul><ul><ul><li>3. intercalating agents . Inserts into DNA and pushes bases apart. Ex. AFLATOXIN - a chemical produced by peanut and grain molds. The mold is Aspergillus flavus (fungus). </li></ul></ul>GA fall08
  60. 61. <ul><ul><li>b. Physical mutagens : </li></ul></ul><ul><ul><ul><li>1. nonionizing radiation - Causes the formation of T= T dimers. UV light @ 260 nm . </li></ul></ul></ul><ul><ul><ul><li>2. Ionizing radiation - damages DNA by causing the formation of “free radicals” leading to mutations. 3 Ex. X-rays . Gamma rays from radioactive fallout penetrates the body. Alpha rays from inhaled dust containing radioactive fallout. </li></ul></ul></ul>
  61. 62. B. TRANSFORMATION <ul><li>The passage of homologous DNA from a dead donor cell to a living recipient cell. Occurs in Streptococcus pneumoniae . When S. pneumo dies the DNA can be absorbed by a living S. pneumo and recombined into the chromosome. The gene for capsule formation is obtained in this way, as is a gene for penicillin resistance . Discovered in 1929 by Fredrick Griffith. </li></ul>GA sp07
  62. 63. Transformation Graphic
  63. 64. Griffith’s Transformation Experiment
  64. 65. C. CONJUGATION <ul><li>1. A “mating” process between a donor F+ (bacteria with fertility factor =plasmid) and an F- recipient cell. </li></ul><ul><ul><li>2. Occurs in Gram - enteric bacteria like E.coli </li></ul></ul><ul><ul><li>3. Discovered in 1946 by Joshua Lederberg and Edward Tatum. </li></ul></ul><ul><ul><li>4. Plasmids carry genes that are nonessential for the life of bacteria. Ex. gene for pili (sex pilus). Ex. plasmid replication enzymes. Ex. Medical Problem: R-Factor = antibiotic resistance! </li></ul></ul>
  65. 66. Conjugation continued <ul><li>“ Normal - Sex” plasmid transfer (usually ~20 of 100 genes). </li></ul><ul><ul><li>a. Requires a sex pilus </li></ul></ul><ul><ul><li>b. F + bacteria transmits a copy of the plasmid to F- bacteria. This converts the F- cell into an F + cell. Medical Problem: The R factor (antibiotic resistance) on the F factor is transmitted ! http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/f.html </li></ul></ul>
  66. 67. <ul><li>6. Hfr ( High Frequency Recombination ) </li></ul><ul><li>a. Hfr- bacterial plasmid integrates into the chromosome. </li></ul><ul><li>b. Medical Problem: Hfr antibiotic resistance genes are passed during binary fission (every time the cell divides). Therefore, antibiotic resistance spreads very rapidly! </li></ul><ul><li>c. When Hfr mate with F – bacteria, only the bacterial genes cross NOT plasmid genes. Genetic diversity results in this case due to recombination. http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/hfr.html </li></ul>
  67. 69. D. TRANSPOSITION p 285 <ul><li>Transposons (jumping genes) are big chunks of DNA that randomly excise and relocate on the chromosome. </li></ul><ul><li>Transposons were discovered in 1950 by Barbara McLintock in corn. </li></ul><ul><li>Causes antibiotic resistance in Staph. aureus, the famous methicillin resistant Staphlococcus aureus (MRSA) strain! </li></ul>
  68. 70. E. TRANSDUCTION <ul><li>the transfer of genetic material from donor bacteria to recipient bacteria via a transducing agent (virus!). Bacterial viruses are called bacteriophage . </li></ul><ul><li>1. Discovered in 1952 by Zinder & Lederberg. </li></ul><ul><ul><li>2. Two kinds of transduction: generalized and specialized. </li></ul></ul>
  69. 72. <ul><ul><li>2. Generalized transduction : Starts with the LYTIC CYCLE where a T- even phage (Fig. 8.5 pg 210) infects E.coli killing the host cell, and synthesizing 2,000 copies of itself. The T-even phage randomly packages bacterial DNA in a few defective phages . Once a T –even phage infects another E. coli , this genetic information can be recombined into the host cell without causing the lytic cycle. New genetic information is thereby transduced from one bacteria to another. </li></ul></ul>
  70. 73. Generalized Transduction
  71. 74. Generalized Transduction
  72. 75. Specialized Transduction <ul><li>3. Specialized transduction </li></ul><ul><li>Lambda phage infects E.coli . The phage does not lyse the cell immediately. Instead it integrates into chromosome of the bacteria as a prophage and remains dormant . This is called the LYSOGENIC CYCLE . Phage genes are replicated and passed to all daughter cells until the bacteria is under environmental stress , from lack of nutrients, etc. Then phage gene will excise from the nucleoid and enter the LYTIC CYLE taking one adjacent gene for galactose metabolism . </li></ul>
  73. 76. Specialized Transduction Cont. <ul><li>The gal transducing phage (lambda) makes ~ 2,000 copies of itself with the gal gene, and infects other E.coli . When gal integrates into the nucleoid of other E. coli , it may provide these bacteria with a new capacity to metabolize galactose. </li></ul>
  74. 77. Specialized Transduction Graphic
  75. 78. Comparison of Bacteriophage <ul><li>3. Comparison of bacteriophage transduction in E.coli . </li></ul><ul><ul><ul><ul><li>Generalized Specialized </li></ul></ul></ul></ul><ul><ul><ul><ul><li>T even phage lambda phage </li></ul></ul></ul></ul><ul><ul><ul><ul><li>lytic cycle lysogenic </li></ul></ul></ul></ul><ul><ul><li>random packaging specific gal gene </li></ul></ul>
  76. 79. End of Slides
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