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Chapter 8: Microbial Genetics

Chapter 8: Microbial Genetics. Genome : genetic information in a cell Chromosome : contains the genes-segments of DNA DNA : nucleotide base pairs - genetic code for proteins Central Dogma : DNA - RNA - Proteins Genomics : sequencing and molecular characterization of genomes. Bacteria

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Chapter 8: Microbial Genetics

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  1. Chapter 8: Microbial Genetics

  2. Genome: genetic information in a cell Chromosome: contains the genes-segments of DNA DNA: nucleotide base pairs - genetic code for proteins Central Dogma: DNA - RNA - Proteins Genomics: sequencing and molecular characterization of genomes Bacteria Single circular chromosome Looped and folded and attached at one or several points to the plasma membrane

  3. THAT SPELLS DNA Jonathan Coulton http://www.jonathancoulton.com/store/downloads/

  4. We start the story when Mom met Dad And they danced all night and he took her home It might have been all the wine they had But they rolled the dice and won your genome Then you grew and you grew and one day you were you And you looked like your father and mother IF you’re looking for someone convenient to blame You can take your pick it’s one or the other DNA, you’re in my heart DNA, in fact you’re in every part of my body Each cell has a nucleus, each nucleus has chromosomes And DNA, baby, that spells DNA

  5. Guanine met Cytosine, fell in love And then Thymine got busy with Adenine They sent the messenger-RNA To the ribosome to make more protein And while it’s killing you dead it will mess with your head And it’s the light in the dark that will guide you It’s the pages and pages of what you are like In the giant book that’s hidden inside you DNA, you’re in my heart DNA, in fact you’re in every part of my body Each cell has a nucleus, each nucleus has chromosomes And DNA, baby, that spells DNA

  6. If it says TGGTCGAAC Then you might get the cancer If it says GTCACGACAGG Then you shouldn’t eat shrimp or nuts If it says TATACACATATCCTCGT Then you’ll probably wish that you didn’t know The time will come when you’re almost gone And you try to guess but you’ll never know You do your best and you soldier on Every day you’re here till it’s time to go All the good things and bad that you do or don’t have You can find out for sure if you got’em But there’s a spiraling staircase that you’re falling down And you’re nothing but dead at the bottom

  7. DNA, you’re in my heart DNA, in fact you’re in every part of my body Each cell has a nucleus, each nucleus has chromosomes And DNA, baby, that spells DNA

  8. Replication Transcription Translation DNA RNA PROTEINS

  9. Replication Transcription Translation DNA RNA PROTEINS • Semiconservative replication: each new DNA molecule contains one original and one new strand • Requires TONS of energy - supplied by the nucleotides (nucleoside triphosphates) *Two phosphates are removed to add the nucleotide to a growing stand *Hydrolysis (exergonic) • Accurate: mistakes made in 1 in every 1010 bases ***Proofreading-DNA pol

  10. Replication Transcription Translation DNA RNA PROTEINS Bacteria: • Some replicate bidirectionally around the chromosome • Two replication forks move in opposite direction away from the origin of replication • Eventually meet when replication is complete Ex: E.coli

  11. file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/dna_replication.swffile:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/dna_replication.swf

  12. TRANSCRIPTION file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/transcription_process.swf

  13. TRANSLATION

  14. file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation_process.swffile:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation_process.swf file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/translation.swf

  15. GENE REGULATION • Turning on and off genes • Save energy and resources • Repression: Turns OFF • Response to overabundance of an end product • Repressors block RNA pol

  16. GENE REGULATION • Induction: Turns ON • Inducer: acts to induce transcription • EX: lac operon • E. coli (bacteria that live in intestines of mammals) • Discovered how genes control the metabolism of the sugar lactose • Lactose: disaccharide made of glucose and galactose • Milk sugar • http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related

  17. When there is/is not lactose LACTOSE PRESENT: It induces E. coli to produce three enzymes which will metabolize lactose LACTOSE ABSENT: three enzymes will not be made. Lactose will not be broken down.

  18. DNA of E.coli Regulator gene: codes for repressor gene Promoter: DNA segment that is recognized by the enzyme RNA pol Operator: DNA segment that serves as a “switch” controlling the access of RNA pol to the promoter Structuralgenes: code for 3 enzymes that break down lactose

  19. Operon “turned off” • Repressor protein attaches to the operator physically blocking RNA pol from attaching RNA pol

  20. Operon “turned on” • Lactose present (acts as inducer starts gene expression) • Binds to the repressor protein • Repressor changes shapes and detaches from operator • RNA pol is not blocked anymore • All three enzymes can be produced

  21. Operator “turned on” lactose

  22. Why is this good? • E. coli is able to turn off and on genes when lactose is present/absent • Bacteria saves resources and produce only those proteins that are needed

  23. Let’s watch it again • http://www.youtube.com/watch?v=oBwtxdI1zvk&feature=related

  24. MuTaTiOnS

  25. GOOD • New enhanced activity that benefits the cell • BAD • Inactive or less active, lethal? • SILENT(neutral) • No change in activity

  26. Types of Mutations Base Substitution (point) • Single base in DNA is replaced Missense mutation: substitution results in an amino acid substitution Nonsense mutation: creates a stop codon in the middle of mRNA....preventing synthesis of protein

  27. Types of Mutations Frameshift • One or a few nucleotide pairs are deleted or inserted in the DNA • Change the reading frame of codons *Mutations can occur spontaneously or by mutagens

  28. MUTAGENS • Chemical: • Nitrous acid (HNO2): causes A to bond with C instead of T

  29. MUTAGENS • Radiation: x-rays, UV rays, gamma rays • Cause electrons to pop out of their usual shells • Ions can combine with bases in DNA, resulting in errors in DNA • Breakage of covalent bonds in sugar-phosphate backbone-breaks in chromosomes

  30. Exposure to UV causes T’s to cross link forming a thymine dimer • Unless repaired, these may cause serious damage or death to the cells because it cannot properly transcibe or replicate. • Some organisms have enzymes that can repair these dimers

  31. Genetic Transfer and Recombination • Conjugation: transfer of a plasmid • Transduction: transfer of DNA via a virus • Transformation: genes transferred from one bacterium to another as “naked” DNA

  32. Conjugation Movement of a plasmid b/w two cells Plasmid: small, self-replicating, gene-containing circular piece of DNA • Requires direct cell to cell contact • Opposite mating types (donor cell has a plasmid, recipient cells do not) file:///Volumes/Tortora_Micro_10e_DVD1/Chapter_08/C_Animations_and_Videos/a_Microbiology_Animations/conjugation.swf

  33. Transduction • Bacterial DNA is transferred from a donor cell to recipient inside a virus that infects bacteria • Bacteriophage (phage)

  34. TRANSFORMATION • First done 70 yrs ago: Griffith • http://www.dnatube.com/video/997/Transformation

  35. HOW DOES THIS HAPPEN? Can happen naturally after cell death and cell lysis • Cell wall becomes permeable to large DNA molecules • Use surface proteins and type 4 pili to extend and take it in • Works best when donor and recipient cells are closely related Artificial transformation: • Competence: when recipient cell is in a physiological state to take up donor DNA • Changing the ionic strength of the medium and heating the cells in the presence of positive ions (Calcium) • Makes cell membrane permeable

  36. We are going to do this!!!

  37. pBLU Transformation • Use an ampicillin-sensitive strain of E. coli, incapable of producing b-galactosidase for lactose breakdown • Induce it to take up pBLU plasmid DNA • Plasmid contains genes for Ampicillin resistance and the entire b-glactosidase gene

  38. http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/14_1.jpghttp://www.biologie.uni-hamburg.de/b-online/library/onlinebio/14_1.jpg

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