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MICROBIAL MODELS:

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INDIRECTLY RESPONSIBLE FOR SYMTOMS. SYMTOMS ARE FROM THE IMMUNE RESPONSE. CLASSIFICATION OF VIRUS ... DEVELOPED THE FIRST VACCINE. SMALLPOX ... – PowerPoint PPT presentation

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Title: MICROBIAL MODELS:


1
CHAPTER 18
  • MICROBIAL MODELS
  • THE GENETICS OF VIRUSES AND BACTERIA

2
  • BACTERIA AND VIRUS STUDIES GAVE SCIENTISTS THE
    ROLE OF DNA IN HEREDITY
  • 1883 ADOLF MAYER
  • SEEKING THE CAUSE OF TOBACCO MOSAIC DISEASE
  • STUNTED THE GROWTH OF TOBACCO PLANTS
  • GAVE LEAVES A MOSAIC APPEARANCE
  • CAUSED BY A VIRUS

3
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4
  • 1890S MARTINUS BEIJERNICK
  • PROPOSED IT WAS CAUSED BY A PARTICLE SMALLER
    THAN A BACTERIA
  • ALSO THE PATHOGEN ONLY REPRODUCED INSIDE THE
    INFECTED HOST
  • ALCOHOL COULD NOT KILL IT
  • COULD NOT BE CULTURED ON MEDIA
  • 1935 WENDELL M. STANLEY
  • CRYSTILLIZED THE INFECTIOUS PARTICLE NOW KNOWN AS
    TMV OR TOBACCO MOSAIC VIRUS

5
  • VIRUS
  • GENOTYPE ENCLOSED IN A PROTEIN COAT
  • 1950S WITH THE HELP OF ELECTRON MICROSCOPY, THE
    VIRUS WAS FINALLY OBSERVED
  • 20 nm IN DIAMETER

6
  • VIRAL GENOME
  • MAY BE DOUBLE OR SINGLE STRANDED DNA OR RNA
  • ORGANIZED AS EITHER SINGLE NUCLEIC ACID MOLECULES
    THAT ARE EITHER LINEAR OR CIRCULAR
  • 4 SEVERAL HUNDRED GENES

7
  • CAPSIDS
  • PROTEIN COAT THAT ENCLOSES A VIRUS
  • ROD SHAPED, POLYHEDRAL OR COMPLEX
  • CAPSOMERES PROTEIN SUBUNITS MADE FROM ONE OR A
    FEW TYPES OF PROTEINS
  • BACTERIOPHAGE
  • MOST COMPLEX CAPSID
  • A VIRUS THAT INFECTS BACTERIA

8
  • ENVELOPE
  • MEMBRANE THAT IS ABLE TO CLOAK CERTAIN VIRAL
    CAPSIDS
  • HELPS A VIRUS INFECT A HOST (SNEAK UP ON IT)
  • DERIVED FROM THE MEMBRANE OF THE HOST CELL

9
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10
  • VIRAL REPRODUCTION
  • A VIRUS IS KNOWN AS AN OBLIGATE INTRACELLULAR
    PARASITE
  • A VIRUS IS ABLE TO EXPRESS ITS GENES ONLY WITHIN
    IN A LIVING (HOST) CELL

11
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12
  • HOST RANGE
  • LIMITED NUMBER OR RANGE OF HOST CELLS THAT A
    PARASITE IS ABLE TO INFECT
  • VIRUS CAN RECOGNIZE A HOST CELL BY A
    COMPLIMENTARY FIT BETWEEN EXTERNAL VIRAL PROTEINS
    AND SPECIFIC RECEPTOR SITES ON THE CELL SURFACE
  • SOME MAY HAVE A BROAD OR NARROW RANGE
  • BROAD FLU, RABIES
  • NARROW
  • INFECT ONLY ONE SPECIES (E. COLI)
  • INFECT A SINGLE TISSUE TYPE (COLD, AIDS)

13
  • THE PATTERN OF A VIRAL LIFE CYCLE
  • INFECTING A HOST CELL WITH THE VIRAL GENOME
  • REPLICATION OF THE VIRAL GENOME
  • MANUFACTURE CAPSID PROTEIN AND ASSEMBLE NEW VIRAL
    NUCLEIC ACID AND CAPSOMERES IN TO THE NEXT VIRAL
    GENERATION

14
  • INFECTING THE HOST CELL
  • T EVEN PHAGES USE A TAILPIECE TO INJECT DNA
    INTO THE HOST CELL
  • ONCE THE GENOME IS INSIDE THE HOST CELL IT
    REPROGRAMS THE CELL TO COPY THE VIRAL GENES AND
    MANUFACTURE CAPSID PROTEIN

15
  • 3 PATTERNS OF VIRAL GENOME REPLICATION
  • DNA-DNA IF VIRAL DNA IS DOUBLE STRANDED, DNA
    REPLICATION RESEMBLES THAT OF THE CELLULAR DNA
    VIRUS. IT WILL USE DNA POLYMERASE PROVIDED BY
    THE HOST
  • RNA-RNA THE HOST CELLS LACK THE ENZYMES TO COPY
    RNA, MOST RNA VIRUS CONTAINS A GENE THE CODES FOR
    RNA REPLICASE. ENZYME WILL USE VIRAL RNA AS A
    TEMPLATE TO PRODUCE COMPLIMENTARY RNA
  • RNA-DNA-RNA SOME RNA VIRUSES ENCODE REVERSE
    TRANSCRIPTASE, AN ENZYME THAT TRANSCRIBES DNA
    FROM AN RNA TEMPLATE

16
  • VIRAL GENES HAVE THE ABILITY TO COMPROMISE ALL OF
    THE HOST CELLS METABOLIC MACHINERY TO PRODUCE
    COPIES OF THE VIRAL GENOME AND CAPSID PROTEINS
  • VIRAL NUCLEIC ACID AND CAPSOMER PROTEINS ASSEMBLE
    SPONTANEOUSLY INTO NEW VIRUS PARTICLES
    (SELF-ASSEMBLY), WHICH LEAVE TO PARASITIZE NEW
    HOST CELLS, OFTEN DESTROYING THE HOST CELL IN THE
    PROCESS

17
  • PHAGES
  • BACTERIOPHAGE IS THE BEST UNDERSTOOD OF ALL
    VIRUSES
  • 1940s SCIENTISTS WERE ABLE TO DEMONSTRATE HOW
  • T PHAGES REPRODUCE IN BACTERIA
  • DEMONSTRATE DNAS GENETIC MATERIAL
  • ESTABLISH PHAGE BACTERIUM AS AN IMPORTANT
    EXPERIMENTAL TOOL

18
  • TWO VIRAL CYLCES
  • LYTIC CYCLE
  • LYSOGENIC CYCLE

19
  • LYTIC CYCLE
  • T 4 LYTIC CYCLE
  • PHAGE WILL ATTACH TO THE CELL SURFACE
  • PHAGE CONTRACTS SHEATH AND INJECTS ITS DNA
  • HYDROLYTIC ENZYMES DESTROY THE HOST DNA
  • PHAGE GENOME DIRECTS THE HOST CELL TO PRODUCE
    PHAGE COMPONENTS (DNA _at_ CAPSID PROTEINS)
  • CELL LYSIS AND RELEASE PHAGE PARTICLES

20
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21
  • BACTERIAL DEFENSES
  • MUTATION CAN ALTER RECEPTOR SITES
  • RESTRICTION ENZYMES (ENDONUCLEASES)
  • HAVE THE ABILITY TO RECOGNIZE AND CUT UP FOREIGN
    DNA

22
  • BACTERIA HOST AND VIRUS
  • CONTINUOUSLY COEVOLVE
  • MOST BACTERIA ARE ABLE TO PREVENT PHAGE ENTRY
  • MOST PHAGES HAVE EVOLVED TO AVOID BACTERIAL
    DEFENSES
  • MANY PHAGES CHECK THEIR DESTRUCTIVE TENDENCIES
    AND MAY COEXIST WITH A BACERIAL HOST

23
  • LYSOGENIC CYCLE
  • VIRUS AND BACTERIA COEXIST WITH A HOST AND WILL
    INCORPORATE THEIR GENOME WITH THE HOST GENOME
  • TEMPERATE (LATENT) VIRUS A VIRUS THAT IS ABLE
    TO INTEGRATE ITS GENOME INTO THE HOSTS GENOME AND
    REMAIN LATENT UNTIL THE LYTIC CYCLE IS INITIATED

24
  • LYSOGENIC CYCLE
  • PHAGE BINDS AND INJECTS ITS DNA INTO HOST
  • PROPHAGE IS FORMED A PHAGE GENOME THAT IS
    INCORPORATED INTO A SPECIFIC SITE ON THE
    BACTERIAL CHROMOSOME
  • ONE ACTIVE PROPHAGE GENE WILL PRODUCE REPRESSOR
    PROTEIN, WHICH WILL SWITCH OFF MOST OF THE
    PROPHAGE GENES
  • PROPHAGE IS COPIED ALONG WITH CELLULAR DNA AS THE
    HOST CELL REPLICATES
  • MAY BE CARRIED FOR MANY GENERATIONS
  • OCCASIONALLY A PROPHAGE MAY LEAVE THE HOST
  • LYSOGENIC CELL IS A HOST CELL THAT IS CARRYING A
    PROPHAGE IN ITS CHROMOSOME

25
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26
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27
  • ANIMAL VIRUS
  • VIRUS WITH ENVELOPES
  • SOME ANIMAL VIRUSES ARE SURROUNDED WITH A
    MEMBRANOUS ENVELOPE
  • THE OUTSIDE CAPSID WILL ENABLE THE VIRUS TO ENTER
    THE HOST CELL
  • IT IS A LIPID BI-LAYER WITH GLYCOPROTEIN SPIKES
    THAT PROTRUDE FROM THE OUTER SURFACE

28
  • PROCESS OF AN ANIMAL VIRUS
  • ATTACHMENT GLYCOPROTEIN SPIKES ATTACH TO THE
    RECEPTOR SITES ON THE HOST
  • ENTRY THE ENTIRE VIRUS IS TRANSPORTED INTO THE
    CYTOPLASM BY RECEPTOR MEDIATED ENDOCYTOSIS
  • UNCOATING THE REMOVAL OF THE PROTEIN CAPSID
  • VIRAL GENOME FUNCTIONS AS A TEMPLATE FOR MAKING
    COMPLEMENTARY RNA STRANDS WITH 2 FUNCTIONS
  • TEMPLATE TO MAKE NEW COPIES OF RNA GENOME
  • SERVE AS m-RNA TO MAKE MORE GLYCOPROTEIN

29
  • ASSEMBLY _at_ RELEASE
  • THE NEW CAPSID AND VIRAL GENOME WILL BE RELEASED
    ENVELOPED TAKING SOME OF THE PLASMA MEMBRANE OF
    THE HOST CELL
  • EXCEPTION
  • HERPES VIRUS ENVELOPE IS DERIVED FROM THE
    NUCLEAR MEMBRANE
  • KNOWN AS A PROVIRUS VIRAL DNA THAT INSERTS INTO
    A HOSTS DNA
  • WILL CREATE RECURRING INFECTIONS, LATENT PERIODS
    THAT ARE FOLLOWED BY A PRODUCTIVE PERIOD (LATENT
    VIRUS)

30
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31
  • VIRAL DISEASE IN ANIMALS
  • DAMAGE OR KILL CELLS
  • MAY BE TOXIC THEMSELVES OR MAY CAUSE THE HOST
    CELL TO PRODUCE TOXINS
  • MAY CAUSE VARYING DEGREES OF CELL DAMAGE (COLDS,
    POLIO, RETROVIRUS-AIDS)
  • INDIRECTLY RESPONSIBLE FOR SYMTOMS
  • SYMTOMS ARE FROM THE IMMUNE RESPONSE

32
  • CLASSIFICATION OF VIRUS
  • TABLE 18.1
  • PAGE 325 TEXTBOOK

33
  • EDWARD JENNER 1796
  • DEVELOPED THE FIRST VACCINE
  • SMALLPOX
  • VACCINES HARMLESS VARIENTS OR DERIVATIVES OF
    MICROBES THAT WILL MOBILIZE THE HOSTS IMMUNE
    SYSTEM
  • WE HAVE NUMEROUS VACCINES TODAY, AND EACH YEAR
    MORE A CREATED
  • MMR, POLIO, CHICKEN POX, INFLUENZA ETC.

34
  • ANTIVIRAL DRUGS
  • ONCE A VIRAL ILLNESS OCCURS LITTLE CAN BE DONE
  • PURINE NUCLEOSIDES, CURRENTLY HAVE BEEN FOUND TO
    INTERFERE WITH VIRAL NUCLEIC ACID SYNTHESIS
  • DNA DNA POLYMERASE
  • RNA RNA REPLICASE

35
  • EMERGING VIRUSES
  • THE APPARENT SUDDEN APPEARANCE AN EXISTING VIRUS
    THAT HAS EXPANDED ITS HOST RANGE
  • MAY OCCUR IF
  • AN INDIVIDUALS IMMUNITY CHANGES
  • SPREADS FROM ONE HOST SPECIES TO ANOTHER
  • DISSEMINATES FROM A SMALL POPULATION TO BECOME
    MORE WIDESPREAD
  • Ex. AIDS, HANTAVIRUS

36
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37
  • ENVIRONMENTAL DISTURBANCES MAY INCREASE VIRAL
    TRAFFIC
  • DEFORESTATION HUMANS MAY COME IN CONTACT WITH
    DIFFERENT ANIMALS THAT MAY HOST A DIFFERENT TYPE
    OF VIRUS
  • NEW ROADS WHICH PREVIOUSLY ISOLATED THE HUMAN
    POPULATION

38
  • VIROIDS _at_ PRIONS (HYPOTHESIS)
  • VIROIDS SMALLER AND SIMPLER THAN A VIRUS. MAY
    DISRUPT PLANT METABOLISM (CURRENTLY HAVE BEEN
    FOUND IN TOMATOES AND COCONUTS)
  • PRIONS (PROTEIN PATHOGENS)
  • DEFECTIVE PROTEINS, MAY BE THE CAUSE OF SCRAPIES
    IN SHEEP (POSSIBLY MAD COW DISEASE) AS WELL AS
    EFFECT THE HUMAN NERVE SYSTEM

39
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40
  • VIRUS _at_ CANCER SOME TUMOR VIRUSES MAY CAUSE
    CANCER. THE TUMOR VIRUS HAS THE ABILITY TO
    TRANSFORM A CELL TO A CANCER CELL
  • ONCOGENES
  • GENES THAT ARE FOUND IN VIRUSES OR PART OF A
    EUKARYOTIC GENOME THAT TRIGGER THE TRANSFORMATION
    OF A NORMAL CELL TO A CANCEROUS CELL

41
  • PLANT VIRUSES (AGRICULTURAL PESTS)
  • STUNT GROWTH (DIMINISH YIELDS)
  • SPREAD VIA
  • HORIZONTAL TRANSMISSION RECEIVE VIRUS FROM AN
    EXTERNAL SOURCE (INSECTS AS VECTORS)
  • VERTICLE TRANSMISSION INHERIT FROM PARENT
  • NO CURRENT CURE FOR PLANT VIRUSES

42
  • EVOLUTION AND VIRUSES
  • VIRUS DO NOT FIT THE FULL DEFINITION OF LIVING,
    HOWEVER
  • HAVE A GENOME WITH THE SAME GENETIC CODE AS
    LIVING THINGS
  • HAVE THE ABILITY TO MUTATE AND EVOLVE
  • MOST LIKELY EVOLVED FROM THE FIRST CELLS

43
  • EVIDENCE
  • GENETIC MATERIAL IS SIMILAR TO THE HOST GENOME
  • SOME VIRAL GENES ARE IDENTICAL TO CELLULAR GENES
    (ONCOGENES _at_ RETROVIRUSES)
  • VIRUS OF EUKARYOTES ARE MORE SIMILAR IN GENOMIC
    STRUCTURE TO THEIR HOSTS THAN BACTERIAL VIRUS
  • VIRAL GENOME ARE SIMILAR TO CERTAIN CELLULAR
    GENETIC ELEMENTS SUCH AS PLASMIDS AND TRANSPOSONS
    (MOBILE GENETIC ELEMENTS)

44
  • GENETICS OF BACTERIA
  • BACTERIAL GENOME IS LARGER THAN THAT OF A VIRUS,
    SMALLER THAN EUKARYOTE
  • SHORT GENERATION SPAN
  • CHROMOSOMES ARE HIGHLY FOLDED AND PACKED WITHIN A
    CELL
  • DNA IN BACTERIUM IS FOUND IN A SINGLE CIRCULAR
    CHROMOSOME
  • NUCLEOID REGION DENSE REGION OF DNA, NOT BOUND
    BY A MEMBRANE
  • PLASMIDS SMALL DOUBLE STRANDED RING OF DNA, MAY
    CARRY EXTRACHROMOSOMAL GENES IN SOME BACTERIA

45
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46
  • BACTERIAL CELLS REPRODUCTION
  • BINARY FISSION
  • RAPID RATE (20 MINUTES IN SOME)
  • IDENTICAL DAUGHTER CELLS
  • MUTATIONS OCCUR DUE TO THE FAST REPRODUCTIVE RATE
  • MUTATION IS THE MAJOR SOURCE OF VARIATION IN
    BACTERIA
  • Ex. E.COLI (INTESTINE OF HUMAN) YOU MAY HAVE 2000
    MUTATIONS IN A 24 HOUR PERIOD

47
  • THERE ARE 3 TYPES OF GENETIC RECOMBINATION IN
    BACTERIA
  • TRANSFORMATION
  • TRANSDUCTION
  • CONJUGATION

48
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49
  • TRANSFORMATION
  • THE PROCESS OF GENE TRANSFER DURING WHICH A
    BACTERIAL CELL ASSIMILATES THE FOREIGN DNA FROM
    ITS SURROUNDINGS
  • SOME BACTERIA TAKE UP NAKED DNA FROM ITS
    SURROUNDINGS
  • ASSIMILATED DNA MAY BE INTEGRATED INTO THE
    BACTERIAL CHROMOSOME BY RECOMBINATION (CROSSING
    OVER)
  • PROGENY WILL CARRY THE NEW GENE COMBINATION
  • THIS TECHNIQUE IS USED IN THE BIOTECHNOLOGY
    INDUSTRY TO PRODUCE PROTEINS CHARACTERISTIC IN
    OTHER SPECIES (INSULIN, HGH)

50
  • TRANSDUCTION
  • GENE TRANSFER FROM ONE BACTERIA TO ANOTHER BY A
    PHAGE
  • GENERALIZED TRANSDUCTION RANDOM PIECES OF THE
    HOST CELL DNA ARE PACKAGED WITHIN A PHAGE CAPSID
    DURING THE LYTIC CYCLE. MAY TRANSFER ALMOST ANY
    HOST GENE, LITTLE PHAGE GENE
  • SPECIALIZED TRANSDUCTION (AKA-RESTRICTED
    TRANSDUCTION) THE TRANSFER OF ONLY CERTAIN GENES,
    THOSE USUALLY FOUND NEAR THE PROPHAGE SITE ON THE
    CHROMOSOME

51
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52
  • CONJUGATION
  • LEDERBERG _at_ TATUM (E. COLI)
  • THE DIRECT TRANSFER OF GENES BETWEEN 2 CELLS
    TEMPORARILY JOINED
  • SEX PILI APPENDAGE USED TO ATTACH THE RECIPIENT
    BACTERIA
  • F FACTOR FOR FERTILITY
  • CONJUGATION OF E. COLI
  • DNA DONATING E. COLI EXTENDS SEX PILI, THE SEX
    PILI ATTACH TO THE DNA RECEIVING CELLS, A
    CYTOPLAMIC BRIDGE FORMS AND THIS IS WHERE THE
    TRANFER OCCURS

53
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54
  • PLASMIDS
  • HAVE ONLY A FEW GENES
  • NOT REQUIRED FOR SURVIVAL OR REPRODUCTION
  • PLASMID GENES CAN BE HELPFUL IN STRESSFULL
    ENVIROMENTS
  • MAY REPLICATE INDEPENDENTLY
  • F _at_ R PLASMIDS

55
  • EPISOMES
  • GENETIC ELEMENT THAT CAN REPLICATE INDEPENDENTLY
    IN THE CYTOPLASM OR INTEGRATED IN THE MAIN
    BACTERIAL CHROMOSOME
  • Ex. CERTAIN PLASMIDS, CERTAIN TEMPERATE VIRUSES
    (LAMBDA PHAGE)
  • PLASMIDS AND VIRUSES BOTH CAN BE EPISOMES
  • PLASMIDS LACK AN EXTRACELLULAR STAGE, HOWEVER
    THEY ARE USUALLY BENEFICIAL
  • VIRUSES ARE USUALLY HARMFUL (PARASITIC)

56
  • F PLASMID _at_ CONJUGATION
  • F --- F- CONJUGATION
  • HFR (HIGH FREQUENCY OF RECOMBINATIN)
  • HFR AND F- CONJUGATION

57
  • R PLASMIDS
  • FOR RESISTANCE, CARRY GENES THAT MAY CONFER
    RESISTANCE TO CERTAIN ANTIBIOTICS
  • R PLASMIDS CAN TRANSFER RESISTANT GENES TO
    BACTERIA OF DIFFERENT SPECIES EVEN PATHOGENIC
    STRAINS DURING CONJUGATION RESULT
  • THE RESISTANT STRAINS OF PATHOGENS ARE BECOMING
    MORE COMMON

58
  • TRANSPOSONS
  • BARBARA McCLINTOCK
  • 1940S TRANSPOSONS IN MAIZE (CORN)
  • 1983 RECEIVED NOBEL PRIZE
  • PIECES OF DNA
  • TRANSPOSABLE GENETIC ELEMENTS THAT CAN MOVE FROM
    ONE CHROMOSOME SITE TO ANOTHER
  • OCCUR AS NATURAL AGENTS OF GENETIC CHANGE IN BOTH
    EUKARYOTES _at_ PROKARYOTES

59
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60
  • THERE ARE 2 PATTERNS OF TRANSPOSONS
  • CONSERVATIVE TRANSPOSITION
  • REPLICATION TRANSPOSTION
  • BOTH OF THESE METHODS ARE DIFFERENT FROM ALL
    OTHER TYPES OF GENETIC RECOMBINATION, THE GENES
    MAY GET SCATTERED RANDOMLY THROUGHOUT THE GENOME

61
  • CONSERVATIVE TRANSPOSITION
  • THE MOVEMENT OF PREEXISTING GENES FROM ONE
    GENOMIC LOCATION TO ANOTHER
  • THE GENES ARE NOT REPLICATED BEFRORE THE MOVE, SO
    THE NUMBER OF GENE COPIES IS PRESERVED

62
  • REPLICATION TRANSPOSITION
  • MOVEMENT OF GENE COPIES FROM THE ORIGINAL SITE OF
    REPLICATION TO ANOTHER LOCATION IN THE GENOME.
    SO THE TRANSPOSON GENES ARE INSERTED AT A NEW
    SITE AND NOT LOST FROM THE ORIGINAL SITE

63
  • INSERTION SEQUENCES
  • THE SIMPLEST TRANSPOSONS CONSIST OF ONLY THE
    GENES (DNA) NEEDED FOR TRANSPOSITION
  • TRANSPOSASE THE ENZYME THAT WILL CATALYZE THE
    INSERTION OF TRANSPOSONS INTO THE NEW CHROMOSOME

64
  • INVERTED REPEATS
  • SURROUND THE TRANSPOSON
  • SHORT NONCODING NUCLEOTIDE SEQUENCES OF DNA THAT
    ARE REPEATED IN REVERSE ORDER
  • CONTAIN ONLY 20-40 NUCLEOTIDE PAIRS
  • RECOGNITION SITES FOR TRANSPOSASE
  • TRANSPOSASE WILL BIND TO THE INVERTED REPEATS AND
    CATALYZE THE CUTTING AND RESEALING OF DNA.

65
  • DIRECT REPEATS
  • 2 OR MORE IDENTICAL DNA SEQUENCES IN THE SAME
    MOLECULE
  • TRANSPOSITION PROCESS CREATES DIRECT REPEATS THAT
    FLANK THE TRANSPOSON AT THEIR TARGET SITE
  • TRANSPOSED INSERTION SEQUENCES SOMEHOW MAY ALTER
    THE CELL PHENOTYPE BY EITHER ALTERING
    TRANSCRIPTION RATES OR TO CREATE MUTATION
  • MOST LIKELY PLAY A MAJOR ROLE IN BACTERIAL
    EVOLUTION

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67
  • COMPOSITE TRANSPOSONS _at_ R PLASMIDS
  • TRANSPOSONS THAT INCLUDE ADDITIONAL GENETIC
    MATERIAL
  • MAY HELP BACTERIA ADAPT TO NEW ENVIRONMENTAL
    CONDITIONS
  • ABLE TO INSERT ANYWHERE ALONG THE STRETCH OF DNA
    THAT IS NOT DEPENDENT IN THE HOMOLOGY OF SEQUENCE
  • Ex. THE GENE FOR ANTIBIOTIC RESISTANCE
  • GENETIC ELEMENTS CONAINING COMPLEX TRANSPOSONS
  • F FACTOR, R PLASMIDS, DNA OF RETROVIRUS

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69
  • CONTROL OF GENE EXPRESSION
  • GENES HAVE THE ABILITY TO SWITCH ON AND OFF AS
    ENVIRONMENTAL CONDITIONS CHANGE
  • THERE ARE 2 WAYS TO CONTROL METABOLISM
  • REGULATION OF ENZYME ACTIVITY
  • REGULATION OF GENE EXPRESSION

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71
  • OPERONS
  • FRANCOIS JACOB _at_ JACQUES MONOD
  • PROPOSED THE OPERON CONCEPT
  • THEY STUDIED THE METABOLISM OF LACTOSE AND E.
    COLI
  • STRUCTURAL GENE THE GENE THAT WILL CODE FOR A
    SPECIFIC POLYPEPTIDE

72
  • OPERON
  • MADE UP OF AN OPERATOR, PROMOTOR, AND THE GENE
    THEY CONTROL
  • A REGULATED CLUSTER OF ADJACENT STRUCTURAL GENES
    WITH RELATED FUNCTIONS
  • COMMON IN PHAGES _at_ BACTERIA
  • HAVE A SINGLE PROMOTOR REGION SO RNA POLYMERASE
    WILL TRANSCRIBE ALL STRUCTURAL GENES, ON AN ALL
    OR NONE BASIS
  • TRANSCRIPTION PRODUCES A SINGLE POLYCISTRONIC RNA
    WITH CODING SEQUENCES FOR ALL OF THE ENZYMES IN A
    METABOLIC PATHWAY

73
  • POLYCISTRONIC RNA
  • LARGE m-RNA MOLECULE THAT IS THE TRANSCRIPT FOR
    SEVERAL GENES
  • MAY BE TRANSLATED INTO SEVERAL POLYPEPTIDES
  • CONTAIN STOP _at_ START CODONS FOR TRANSLATION OF
    EACH POLYPEPTIDE

74
  • OPERATOR
  • DNA SEGMENT BETWEEN AN OPERONS PROMOTOR _at_
    STRUCTURAL GENE.
  • CONTROLS THE ACCESS OF RNA POLYMERASE TO THE
    STRUCTURAL GENE
  • ACTS AS AN ON/OFF SWITCH
  • THE CONTROL POINT FOR TRANSCRIPTION

75
  • REPRESSOR
  • CONTROLS ON/OFF
  • A PROTEIN THAT SWITCHES OFF THE OPERON
  • BINDS TO THE OPERATOR AND BLOCKS ATTACHMENT OF
    RNA POLYMERASE TO THE PROMOTOR
  • SPECIFIC ACTIVE SITE, IT HAS NO EFFECT ON OTHER
    OPERONS

76
  • REGULATORY GENES
  • ENCODES REPRESSORS
  • LOCATED SOME DISTANCE AWAY FROM OPERONS THAT THEY
    CONTROL
  • PRODUCE REPRESSOR CONTINUOUSLY
  • NOT ALWAYS ABLE TO BLOCK TRANSCRIPTION
  • ALTERNATE BETWEEN ACTIVE _at_ INACTIVE CONFORMATION

77
  • REPRESSOR
  • ACTIVITY DEPENDS ON THE PRESENCE OF KEY
    METABOLITES IN THE CELL
  • REGULATION OF THE TRP OPERON IN E. COLI IS AN
    EXAMPLE OF HOW A METABOLITE CUES THE REPRESSOR
  • REPRESSIBLE ENZYMES CATALYZE THE ANABOLIC PATHWAY
    THAT WILL PRODUCE THE A.A. (TRYPTOPHAN)
  • THE ACCUMULATION OF THE A.A. REPRESSES THE
    SYNTHESIS OF THE ENZYMES THAT CATALYZE ITS
    PRODUCTION

78
  • TRANSCRIPTION OF REGULATORY ENZYME
  • PRODUCES
  • m-RNA
  • GETS TRANSLATED INTO
  • REGULATORY PROTEIN
  • THAT WILL BIND TO
  • OPERATOR
  • REPRESSES OR ACTIVATES
  • TRANSCRIPTION OF OPERONS STRUCTURAL GENE

79
  • TRYPTOPHAN ACTIVATES THE REPRESSOR BY
  • REPRESSOR PROTEIN HAS A DNA BINDING SITE, PLUS
    ALLOSTERIC SITE THAT IS SPECIFIC FOR TRYPTOPHAN
  • TRYPTOPHAN BINDS TO THE REPRESSORS ALLOSTERIC
    SITE AND ACITIVATES THE REPRESSOR AND CAUSES IT
    TO CHANGE ITS CONFORMATION
  • THE ACTIVATED REPRESSOR BINDS TO THE OPERATOR
    WHICH SWITCHES TRP OPERON OFF
  • TRYPTOPHAN OPERATES AS A COREPRESSOR

80
  • COREPRESSOR
  • A MOLECULE THAT BINDS TO A REPRESSOR PROTEIN
    CAUSING IT TO CHANGE ITS CONFORMATION
  • ONLY THE REPRESSOR COREPRESSOR COMPLEX CAN
    ATTACH TO AN OPERATOR AND TURN OFF THE OPERON
  • AS THE TRYPTOPHAN CONCENTRATION INCREASES IT
    TURNS OFF ITS OWN PRODUCTION BY ACTIVATING THE
    REPRESSOR

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82
  • NEGATIVE GENE REGULATION
  • REPRESSABLE ENZYMES ENZYMES WHICH HAVE THEIR
    SYNTHESIS INHIBITED BY A METABOLITE (TRYPTOPHAN)
  • INDUDUCABLE ENZYMES ENZYMES WHICH HAVE THEIR
    SYNTHESIS STIMULATED OR INDUCEDBY SPECIFIC
    METABOLITES (LACTOSE)

83
  • LACTOSE METABOLISM (E.COLI)
  • PROGRAMMED BY THE LAC OPERON
  • LAC Z CODES FOR GALACTOSIDASE WHICH WILL
    HYDROLYZE LACTOSE
  • LAC Y CODES FOR PERMEASE, A MEMBRANE PROTEIN
    THAT TRANSPORTS LACTOSE INTO THE CELL
  • LAC A CODE FOR TRANSACYLASE, ENZYME PRESENT
    (NO KNOWN ROLE YET)
  • LAC OPERON HAS A SINGLE PROMOTOR AND OPERATOR
    AND IS INNATELY ACTIVE
  • ALLOLACTOSE (ISOMER OF LACTOSE) ACTS AS AN INDUCER

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  • ALLOLACTOSE
  • INACTIVATED REPRESSOR LOSES AFFINITY FOR THE
    LAC OPERON
  • OPERON IS TRANSCRIBED
  • ENZYMES ARE PRODUCED FOR LACTOSE METABOLISM

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  • REPRESSABLE ENZYMES
  • GENES ARE SWITCHED ON UNTIL A SPECIFIC METABOLITE
    ACTIVATES THE REPRESSOR
  • GENERALLY FUNCTION IN ANABOLIC PATHWAYS
  • PATHWAY END PRODUCT SWITCHES OFF ITS OWN
    PRODUCTION BY REPRESSING ENZYME SYNTHESIS

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  • INDUCIBLE ENZYMES
  • THEIR GENES ARE SWITCHED OFF UNTIL A SPECIFIC
    METABOLITE INACIVATES THE REPRESSOR
  • FUNCTION IN CATABOLIC PATHWAYS
  • ENZYMES SYNTHESIS IS SWITCHED ON BY THE NUTRIENT
    THE PATHWAY USES

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  • POSITIVE CONTROL
  • OCCURS ONLY IF AN ACTIVATOR MOLECULE INTERACTS
    DIRECTLY WITH THE GENOME TO TURN ON TRANSCRIPTION

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  • POSITIVE GENE REGULATION
  • CYCLIC AMP (Camp)
  • ACCUMULATES WHEN GLUCOSE IS ABSENT
  • MONITORS THE CONCENTRATION OF GLUCOSE

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  • Camp RECEPTOR PROTEIN (CRP)
  • A REGULATORY PROTEIN
  • ACTIVATES TRANSCRIPTION
  • BASED ON THE RELATIVE CONCENTRATION OF GLUCOSE
  • GLUCOSE SCARCE CAMP ACTIVATES CRP AND LAC
    OPERON PRODUCES ABUNDANT m-RNA FOR THE LACTOSE
    PATHWAY
  • GLUCOSE PRESENT CAMP IS SCARCE AND CRP IS
    UNABLE TO STIMULATE TRANSCRIPTION
  • THIS PATHWAY INSURES THAT E.COLI WILL CONSUME
    LACTOSE ONLY IF GLUCOSE IS UNAVAILABLE

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