Prokaryotes - Bacteria and Archaea Lecture Powerpoint

							  Origin of Life
Prokaryotic Cells

   Introduction to Biology
        James Dauray
       Origin of Cellular Life
• The Earth formed about 4.6 billion years ago.
   o For about 500 million years, the Earth was continually
     bombarded by chunks of rock and ice in the solar system.
• The early atmosphere of Earth contained:
   o   Water vapor H2O
   o   Nitrogen N2
   o   Carbon dioxide CO2
   o   Methane CH4
   o   Ammonia NH3
      Origin of Cellular Life
• How did life arise from such a harsh environment?
• Two scientists designed a model of what conditions
  were like on Earth at this time.
   o This is called the Miller-Urey Apparatus
Miller-Urey Apparatus
              • This apparatus
                simulated three
                important
                conditions on
                Earth:
                –   The high amount
                    of lightning
                –   Heat and gases
                    released by
                    volcanic activity
                –   Water vapor
                    present in the
                    atmosphere.
       Results of Miller-Urey
            Apparatus
• Simple compounds including water (H2O), methane
  (CH4), ammonia (NH3), and hydrogen (H2) were used to
  simulate the atmosphere.
• After 2 weeks, 10-15% of the carbon had been used to
  form sugars, amino acids, and parts of nucleic acids.
  o These simple organic compounds could have produced the
    proteins, lipids, and carbohydrates that make up life today.
                 The First Cells
• The first life forms on Earth were likely single-celled
  prokaryotic organisms.
• Prokaryotic organisms are single-celled organisms
  that do not have a nucleus.
   o Their DNA or RNA is usually floating freely inside the cell.
• Prokaryotic cells also do not have any membrane
  bound organelles.
• Most prokaryotes are microscopic, but what
  they lack in size they make up for in numbers.
• There are more in a handful of fertile soil than
  the number of people who ever lived.
• Prokaryotes thrive almost everywhere,
  including places too acidic, too salty, too
  cold, or too hot for most other organisms
• They have an astonishing genetic diversity
           Prokaryotic Energy
                Sources
• Prokaryotes are able to get the energy they
  need for life from four different sources:
    o   Photoautotrophy
    o   Chemoautotrophy
    o   Photoheterotrophy
    o   Chemoheterotrophy
•   “Photo” means light.
•   “Chemo” means inorganic (non-living) chemicals.
•   “Auto” means self.
•   “Hetero” means different.
  Relationships to Oxygen
• Prokaryotic metabolism varies with respect to
  oxygen:
  o Obligate aerobes require oxygen
  o Facultative anaerobes can survive with or without oxygen
  o Obligate anaerobes are poisoned by oxygen
                       Archaea
• Archaea are prokaryotic organisms that are
  very similar to bacteria in size and structure.
• Bacteria and archaea likely evolved
  separately from the original life forms on Earth.
• Key differences between bacteria and archaea:
  o Archaea can survive in extremely hot, cold, and salty environments.
  o Archaea are not affected by many antibiotics.
  o Archaea are obligate anaerobes; they can only survive in oxygen-
    free environments.
• Archaea can be classified by the type of
  environment they live in:
  o Extreme thermophiles thrive in very hot environments
  o Extreme halophiles live in high saline environments
  o Acidophiles live in environments with a very low pH (high
    amounts of acid).
            Reproduction
• Prokaryotes reproduce quickly by binary
  fission and can divide every 1–3 hours.
  o Binary fission is asexual reproduction and
    produces exact clones of the original bacteria.
• Many prokaryotes form endospores, which
  can remain viable in harsh conditions for
  centuries
             Reproduction
• Prokaryotes are able to reproduce so quickly that
  under the right conditions they grow exponentially.




• Exponential growth is when the population
  increases at a faster and faster rate.
• This only occurs if all the needs of the bacteria
  culture are met (food, space, etc).
               Petri Dishes
• Bacteria are cultured in petri dishes, which contain
  agar, a food source.
• Petri dishes are close to perfect conditions for
  bacteria to grow, so they reproduce exponentially.
• Prokaryotes like bacteria are able to evolve
  much more quickly than multicellular
  organisms.
  o They reproduce quickly.
  o Their genome is small, so a single mutation can
    change a bacteria drastically.
  o Prokaryotes are able to exchange plasmids
    with each other through pili.
            Bacterial Shapes
• Most prokaryotes are unicellular, although
  some species form colonies
• Prokaryotic cells have a variety of shapes
• The three most common of which are:
  o Coccus – Spherical
  o Bacillus – Rod-shaped
  o Spirilla – Spiral-shaped




                          Video: Tubeworms
LE 27-2




               1 µm        2 µm           5 µm
          Spherical   Rod-shaped      Spiral
            (cocci)       (bacilli)
                Pili

                       Nucleoid

                         Ribosomes

                            Plasma
                            membrane

                             Cell wall
    Bacterial
chromosome                         Capsule
                                                               0.5 µm
                                  Flagella



   A typical                                 A thin section through the
   rod-shaped                                bacterium Bacillus
   bacterium                                 coagulans (TEM)
• Most prokaryotes have a ring of DNA that is
  not surrounded by a membrane.
   o No nucleus.
   o DNA is kept within a nucleoid region instead.
• Some species of bacteria also have smaller
  rings of DNA called plasmids.
   o These can be exchanged between invididuals.
• DNA provides instructions to ribosomes, which
  produce any proteins the bacteria need.
LE 27-8

          Chromosome




                       1 µm
        Internal Structures
• Prokaryotic cells do not have membrane-
  bound organelles.
  o Ex: Chloroplast, mitochondria
• However, some prokaryotes have special
  membranes that perform some of the same
  functions.
  o Thylakoid membranes enable photosynthesis
  o Respiratory membranes enable the use of oxygen to break
    down nutrients into ATP.
LE 27-7

                        0.2 µm                        1 µm




          Respiratory
           membrane



                                         Thylakoid
                                        membranes


   Aerobic prokaryote            Photosynthetic prokaryote
    Cell-Surface Structures
• An important feature of nearly all prokaryotic
  cells is their cell wall.
• The cell wall…
  o Maintains cell shape
  o Provides physical protection
  o Prevents the cell from bursting in a hypotonic
    environment
• The cell wall of many prokaryotes is covered by a
  capsule, a layer of polysaccharides that protect them
  from being caught by white blood cells.




                        Capsule
       Fimbriae



• Some prokaryotes have fimbriae and pili, which
  allow them to stick to their growing surface or
  attach to other prokaryotes to exchange genes..
                    Motility
• Most motile bacteria propel themselves by
  flagella.
• In the environment, many bacteria exhibit the
  ability to move toward or away from certain
  stimuli




            Video: Prokaryotic Flagella (Salmonella typhimurium)
    LE 27-6




                        Flagellum




                                     Filament

                                                50 nm

Cell wall                     Hook


                       Basal apparatus




              Plasma
            membrane
Importance of Prokaryotes
• Prokaryotes are so important to the biosphere
  that if they were to disappear, most other life
  would not be able to survive.
  Symbiotic Relationships
• Symbiotic relationships are when two
  organisms live close together.
• In mutualism, both symbiotic organisms
  benefit
  o Example: Bacteria that live in deep-sea fish,
    producing bioluminescence.
• In commensalism, one organism benefits while
  neither harming nor helping the other.
  o Example: Most of the bacteria on human skin
     Nitrogen Metabolism
• Prokaryotes also need
  nitrogen to build amino
  acids and proteins.
• One common source of
  nitrogen is called nitrogen
  fixation, where prokaryotes
  convert atmospheric
  nitrogen to ammonia.
• Some plants, called
  legumes, have nodules in
  their roots that contain
  bacteria to help them fix
  nitrogen.
      Chemical Recycling
• Prokaryotes help recycle elements needed for
  life between living and nonliving parts of the
  ecosystem.
• Heterotrophic prokaryotes function as
  decomposers, breaking down corpses, dead
  vegetation, and waste products into smaller
  molecules that can be used by other living
  things.
         Bioluminescence
• Some bacteria produce light as a result of their
  internal chemical reactions.
• Other animals have formed mutualistic relationships
  with these bacteria to take advantage of this
  bioluminescence.
         Harmful Bacteria
• In parasitism, one organism, called a parasite,
  benefits at the expense of the host
  o Example: The bacteria that causes strep
    throat.
• Not all prokaryotes are harmful, but some are
  human pathogens – they cause disease.
   Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
  diseases
• Lyme disease is one example.
• Pathogenic prokaryotes typically cause
  disease by releasing exotoxins or endotoxins
• Exotoxins are released externally by the
  bacteria, often as waste products.
  o Example: Botulism, tetanus, anthrax
• Endotoxins are released only when bacteria
  die and their cell walls break down
  o Example: Meningitis
                   Antibiotics
• Antibiotics are anti-bacterial chemicals that
  originally came from mold.
• Each antibiotic works in different ways.
   o Penicillin disrupts the bacteria’s ability to produce a cell
     wall, causing it to burst due to an influx of water into its
     cytoplasm.
      Antibiotic Resistance
• Bacteria can mutate and evolve quickly, due to
  their small size and fast reproduction rate.
• Sometimes, a mutation will result in their ability to
  resist the action of antibiotics.
   o Over time, this mutation can spread throughout an entire
     colony, creating a strain of antibiotic-resistant bacteria.
• Resistant bacteria will not be
  affected by the antibiotics in
  the same way.