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					          Prokaryotes
(the fancy way to say Bacteria)
         Chapter 27




                                  1
                    Outline

•   Prevalence of Prokaryotes
•   Prokaryotic Diversity
•   Prokaryotic Complexity
•   Prokaryotic Variation
•   Prokaryotic Metabolism
•   Human Bacterial Diseases
•   Benefits of Prokaryotes


                                2
             Prevalence of Prokaryotes

•   In almost every place or environment
    microbiologists (scientists who study small
    organisms) look, prokaryotes have been found.
     – Hot springs, hypersaline environments, highly

       toxic gaseous environment, within clean
       rooms of hospitals
•   In the 1980’s a new method of classification
    was used
•   Divided prokaryotes into 2 groups:
     – Archaebacteria (Archae) and bacteria
                                                   3
            Prevalence of Prokaryotes

•   Prokaryotes are the oldest, structurally
    simplest, and most abundant forms of life on
    earth.
     – abundant for over 2 billion years before

       the appearance of eukaryotes
     – Prokaryotic synthesis (from cyanobacteria)

       is thought to have been the source for
       much of the earth’s oxygen in atmosphere
     – 5,000 different kinds currently recognized



                                                    4
Structure of a Prokaryotic Cell




                                  5
          Structure of a Prokaryotic Cell

•   Most prokaryotic cells are small and lack
    interior organization.
•   The plasma membrane is enclosed within a
    rigid cell wall
•   DNA not contained within a membrane-
    bounded nucleus.
•   Prokaryotes exteriorly may have a flagellum
    and other outgrowths called pili.
•   Pili aid in attachment to other cells
                                                  6
            Prevalence of Prokaryotes

•   Prokaryotic form
     – bacillus (bacilli) straight and rod-shaped

     – coccus (cocci) spherical shaped

     – spirillum (spirilla) long and helical shaped

•   Some bacillus and coccus bacteria form
    colonies
•   Spirilla generally do not form colonies and
    are often free swimming
•   Some bacterial colonies form spore
    producing structures.
                                                      7
Prevalence of Prokaryotes

•Prokaryotic form
Coccus
  – Diplococcus

      pairs

  – Streptococcus

      chains

  – Tetrad

      quads



                            8
           Prevalence of Prokaryotes

Coccus
 Sarcina



 Staphalo




                                       9
           Prevalence of Prokaryotes

Bacillus
Single



Strepto



coccobacillus (no pics)

                                       10
                Prevalence of Prokaryotes

Spiral Types

Vibrio
Comma shaped

Sprillium
Thick rigid spiral

Spirochete
Thin flexible

                                            11
                    Prevalence of Prokaryotes
•   Prokaryotes versus Eukaryotes
     – unicellularity
            some may form filamentous matrices
    –   cell size
            1 μm or less in diameter
            May vary by 5 orders of magnitude
    –   chromosomes
            “naked” (no protein) circular DNA located in nucleoid
    –   cell division and recombination
            binary fission (asexual)
    –   internal compartmentalization
            No internal compartments (mitochondria or chloroplasts)
            only organelle is the ribosome
    –   flagella
            Single protein flagella of flagellin
            Spin like propellers instead of whiplike
    –   metabolic diversity
            Several kinds of anaerobic and aerobic photosynthesis
            Chemoautotrophs                                           12
               Prokaryotic Diversity

•   Original key classification characteristics
    – photosynthetic or nonphotosynthetic

    – motile or nonmotile

    – unicellular or colony-forming or

      filamentous
    – spore formation by division or transverse

      binary fission



                                                  13
              Prokaryotic Diversity

•   Now prokaryotic classification completed
    with genetic and molecular approaches
    – Analysis of amino acids sequence of key

      proteins
    – Nucleic acid analysis by establishing %

      guanine (G) and cytosine (C)
    – nucleic acid hybridization

    – ribosomal RNA sequencing

    – whole genome sequencing


                                                14
              Kinds of Prokaryotes

•   Very early, prokaryotes split into two lines
    – Archaea and bacteria are as different in

      structure and metabolism from each other
      as either is from eukarya.
        Archae (archebacteria) not actually as

         old as Bacteria




                                                   15
                Prokaryotic Diversity
•   Comparing archaebacteria and bacteria
    – plasma membranes

        composed of different lipids

    – cell wall

        archaebacteria lack peptidoglycan

    – gene translation machinery

        Bacteria ribosomal proteins and RNA
         polymerases different from eukaryotes
        archaebacteria similar to eukaryotes

    – gene architecture

        bacteria genome not interrupted by introns

        some archaebacteria posses introns


                                                      16
                Prokaryotic Complexity
•   Prokaryotic cell surface – identifying features
    – cell wall maintains shape and protects the cell

      from swelling and rupturing
         usually consist of peptidoglycan

             Gram-positive - thicker peptidoglycan

                (purple color after stain)

             Gram-negative - thinner peptidoglycan

                (red color after stain)

    – flagella – slender protein - locomotion

    – pili - hairlike structures – attachment (7.5 – 10 nm)

    – endospores - resistant to environment


                                                          17
Gram Stain




             18
Flagellar Motor




                  19
                     The Cell Interior
•   Internal membranes
     – invaginated plasma membrane for respiration and/or

       photosynthesis
•   Nucleoid region
     – lack nucleus - genes encoded with single double-

       stranded DNA
     *Prokaryotes often posses plasmids: independently
       replicating circle of DNA that contain only a few genes
       (not usually essential for survival)
•   Ribosomes
     – Prokaryotic ribosomes are smaller than eukaryotic

       ribosomes, and differ in protein and RNA content.
     – Some antibiotics (tetracycline and chloramphenicol) bind

       to prokaryotic ribosomes to block protein synthesis

                                                                  20
                     The Cell Interior
•   Internal membranes
     – (a) aerobic bacterium exhibits extensive respiratory

       membranes within cytoplasm
     – (b) cyanobacterium has thylakoid-like membranes that

       provide sites for photosynthesis

•   Do you think that it
    is likely that
    photosynthetic and
    respiratory
    membranes evolved
    more than once?
•   How could your
    idea be tested
    experimentally?
                                                              21
  Processes to Create Prokaryotic Variation
mutation
  – spontaneous errors in DNA replication

      prokaryotic ability to mutate rapidly often has

       adverse effect on humans
  – Radiation, UV light, and various chemicals

    (mutagens) cause DNA replication errors
  – Normal mutation rate 1 per million bases

  – E. coli has 5000 genes

  – This means that 1 out of every 200 bacteria will

    have a mutation
  – 1 spoonful of soil has 1 billion bacteria, so there

    should be 5 million mutant individuals per
    spoonful!                                             22
    Processes to create Prokaryotic Variation
mutation
  – with sufficient nutrients, a typical bacterium

    population could double in 20 minutes.
  – this allows for mutations to spread rapidly

  – individual bacterium not killed by an antibiotic can

    then reproduce rapidly and after 30 generations (10
    hours) there would be over 1 billion clones of this
    resistive bacteria
  – Some hospitals now have strains of Staphyloccus

    aureus that are penicillin resistant
  – Why then could antibiotic soaps be a problem?

  – Why should you take all 10 days of your

    medication?
                                                       23
 Processes to create Prokaryotic Variation
mutation –figure 27.7




                                             24
    Processes to create Prokaryotic Variation

•   genetic recombination
     – occurs by gene transfer from one cell to

       another by viruses or conjugation
         conjugation: temporary union of 2

          unicellular organisms, during which
          genetic material is transferred from one
          cell to another.
     – this is another method that can lead to

       resistant bacteria

                                                     25
                    Prokaryotic Metabolism
•   Autotrophs
    – obtain carbon from inorganic CO2

        photoautotrophs – use sunlight to build organic

         molecules from CO2
               chlorophyll a as pigment and H20 as electron donor
               bacteriochlorophyll as pigment and H2S as electron donor
          chemoautotrophs - inorganic chemicals
             obtain energy by oxidizing inorganic

              substances
             Nitrifiers – oxidize ammonia or nitrite

             On ocean floors H2S is oxidized as it escapes
                from thermal vents
                                                                           26
              Prokaryotic Metabolism
•   Heterotrophs
    – obtain carbon from organic molecules

        photoheterotrophs – sunlight + organic C

           purple non-sulfur bacteria

           organic molecules such as

            carbohydrates or alcohols source for C
        chemoheterotrophs (most prokaryotes)

           carbon and energy from organic

            molecules
           most decomposers and pathogens

                                                 27
              Prokaryotic Metabolism

•   How heterotrophs infect host organisms
    – proteins secreted by type III system

        may be used to transfer other virulence

         proteins into nearby eukaryotic cells




                                                   28
            Human Bacterial Diseases
•   Tuberculosis
    – afflicts respiratory system and easily

      transmitted from person to person through
      the air
•   Dental caries
    – tooth decay caused by bacteria present in

      plaque
        high sugar diets increase tooth decay

            lactic acid bacteria ferment sugars and

             reduce pH, thus degenerating tooth
             enamel
                                                   29
           Human Bacterial Diseases

•   Sexually transmitted diseases
    – Gonorrhea (Neisseria gonorrhoeae)

    – Syphilis (Treponema pallidum)

    – Chlamydia (Chlamydia trachomatis)




                                          30
             Benefits of Prokaryotes

•   Environment
    – chemical cycling

    – decomposition

    – nitrogen fixation

        reduces N2 to NH3

•   Symbiotic properties
    – nitrogen-fixation

    – digestive tract of animals



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             Benefits of Prokaryotes

•   Genetic engineering
    – nonpolluting insect control

    – bioremediation

        pollutant removal

    – biofactories

        commercial production of antibiotics

•   Bioweapons
    – anthrax

    – smallpox
                                                32
Bioremediation




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