Prokaryotes (the fancy way to say Bacteria)

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Prokaryotes(the fancy way to say Bacteria)

• Chapter 27

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Outline

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

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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 1980s a new method of classification was
  used
• Divided prokaryotes into 2 groups
• Archaebacteria (Archae) and bacteria

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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
  earths oxygen in atmosphere
• 5,000 different kinds currently recognized

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Structure of a Prokaryotic Cell
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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

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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.

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Prevalence of Prokaryotes

• Prokaryotic form
• Coccus
• Diplococcus
• pairs
• Streptococcus
• chains
• Tetrad
• quads

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Prevalence of Prokaryotes

• Coccus
• Sarcina
• Staphalo

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Prevalence of Prokaryotes

• Bacillus
• Single
• Strepto
• coccobacillus (no pics)

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Prevalence of Prokaryotes

• Spiral Types
• Vibrio
• Comma shaped
• Sprillium
• Thick rigid spiral
• Spirochete
• Thin flexible

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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

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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

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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

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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

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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

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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

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Gram Stain
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Flagellar Motor
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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

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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?

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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!

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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?

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Processes to create Prokaryotic Variation

• mutation figure 27.7

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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

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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

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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

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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

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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

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Human Bacterial Diseases

• Sexually transmitted diseases
• Gonorrhea (Neisseria gonorrhoeae)
• Syphilis (Treponema pallidum)
• Chlamydia (Chlamydia trachomatis)

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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

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Bioremediation