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Bacteria and Viruses

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					Viruses and Prokaryotes
           What is a Virus?
• A virus is a noncellular particle made up
  of genetic material and protein that can
  invade living cells
• Structure
  – Core of nucleic acid surrounded by a protein
    coat called a capsid
  – Capsid can be DNA or RNA, but not both
  – Core can be several to several hundred
    genes
       SO HOW BIG ARE
         VIRUSES???
• Viruses are REALLY
  small.
• They are much smaller
  than bacteria.
• They can only be seen
  with an electron
  microscope.
              Bacteriophage
• Bacteriophages are viruses that infect
  bacteria
• Bacteriophage
  – Head – capsid and DNA
  – Tail – with fibers to attach to bacteria
                   T group
• Most commonly studied are T group – T1,
  T2, T3, T4 etc...
• T4 has a DNA core within a protein coat,
  and tail with tail fibers to attach to bacteria.
               Viral shapes
• Variety of shapes
  – Rod
  – Tadpole
  – Many sided, helical or cubelike
       VIRUS SHAPES

• Round
• Rod-shaped
• Many sided
  (icosohedral)
                 SHAPES MAY DIFFER BUT…
• All viruses have
• 1. Chromosome-like part that carries hereditary information – The Core
• 2. Protein coat: Protects hereditary information and provides the shape! The
  Capsid
                                          Tobacco Mosaic
             T4 Bacteriophage                  Virus
                                                                                 Influenza
                                                            RNA                    Virus
                                DNA
    Head
                                                                                             RNA
                                                           Capsid     Capsid
                                                           proteins


    Tail
    sheath
                                  Tail
                                  fiber



                                                                      Surface
                                                                      proteins           Membrane
                                                                                         envelope
      ROUND VIRUSES
• Herpes virus
 –There are
  two types:
   • Genital
   • oral
ROD-SHAPED

     • Tobacco
       mosaic
       virus
        MANY SIDED

• bacteriophage




     E coli bacteria
 Is this why viruses infect us?
                • YES!
                • Viruses need
                  living
                  organisms in
                  order to
                  reproduce and
                  form more
                  viruses!
Injecting DNA virus
                 Virus Size
• Size – 20 to 400 nanometers (one
  nanometer is one billionth of a meter)
• Specificity – usually infect specific
  organisms
  – Cannot infect animals if it infects plants
  – Some can infect wider variety
  – Rabies – all mammals, some birds
VIRUSES ARE SPECIFIC IN
THE CELLS THEY INFECT
Tobacco mosaic virus: only tobacco
plants…not wheat or corn


Rabies: only nervous system cells of mammals



Common cold: infects cells on airway passage to
lungs
                       Lytic Infection
•   Cause cells to lyse or burst

1. Infection – chance contact virus with right kind of bacterium. Virus
   attaches to bacterium and injects its DNA. Most times, complete
   virus particle does not enter.
2. Growth – Bacterium can’t tell difference between bacterial and viral
   DNA. RNA polymerase causes mRNA to be made from cell for
   virus. Viral DNA takes over and produces more DNA and viral
   proteins.
3. Replication – Virus uses bacterial material to make thousands of
   copies of the protein coat and DNA. Cell becomes filled with virus
   particles. (All three stages can happen with E. coli within 25
   minutes!)
4. DNA serves as central point for virus particles to be assembled.
   Cells fill with virus and lyse (burst). New viruses can now infect new
   cells.
SO HOW DO VIRUSES CAUSE
       DISEASE?
 Section 19-3
                                       Bacteriophage           Bacteriophage DNA
                                       protein coat
                                                                          Bacterial
                                                                          chromosome




                                           Bacteriophage attaches to
                                           bacterium’s cell wall

    Bacteriophage enzyme lyses the
    bacterium’s cell wall, releasing
    new bacteriophage particles that
    can attack other cells.
                                               Lytic Cycle


                                                                                   Bacteriophage injects DNA
                                                                                   into bacterium




      Bacteriophage proteins and
      nucleic acids assemble into
      complete bacteriophage
      particles                                                                         Bacteriophage
                                        Bacteriophage takes over
                                        bacterium’s metabolism, causing                 Bacteriophage DNA
                                        synthesis of new bacteriophage
                                                                                        Bacteriophage protein
                                        proteins and nucleic acids
                Retroviruses
• RNA viruses
• When they infect a cell, they produce DNA
  copies of their RNA genes.
• Retroviruses have their genetic information
  copied backwards. RNA  DNA
• One retrovirus is HIV. Others cause cancer in
  animals and humans.
• The theory is that viruses were not the first living
  things. They are dependent on living things to
  survive.
EUBACTERIA AND
ARCHAEBACTERIA:
  The two bacterial
     kingdoms

               Bacteria on a pin head
                Eubacteria
• “True” bacteria
• largest Kindgom of prokaryotes
• generally surrounded by cell wall composed of
  complex carbohydrates
• have a cell membrane (some have 2 cell
  membranes)
• Some have flagella for movement
• Found everywhere
• Some produce disease
• Some photosynthetic
• some very useful – cheese is just one example
     PROKARYOTIC CELLS
• Prokaryote – what does that mean?
  Classification of Prokaryotes
• All prokaryotes were in kingdom Monera.
• Now – 2 kingdoms
  – Eubacteria and archaebacteria
           Archaebacteria
• Archaebacteria includes organisms that
  live in very harsh environments
• Methanogens – live in oxygen free
  environments – mud, digestive tracts of
  animals
• Extremely salty environments
• Hot springs
          Identifying Bacteria
• Cell Shape
  – Rod – bacilli
  – Sphere – cocci
  – Spiral – spirilla
  Bacterial Shapes




Round   Rod          Spiral
             Arrangement
• 2 cocci – diplococci
• long chains – streptococci
• clumps, clusters – staphylococci
                    Cell Wall
• Chemical nature – Gram staining
• Hans Christian Gram
• 2 dyes – crystal violet (purple) and safranine
  (red)
  – bacteria either take one or the other
  – If only one thick layer of carbohydrate and protein
    molecules outside the cell membrane – picked up
    crystal violet – appeared purple – GRAM POSITIVE
  – If cell had 2nd, outer layer of lipid and carbohydrate –
    picked up safranine – appeared red GRAM
    NEGATIVE
        Bacterial movement
• propelled by flagella
• lash, snake, or spiral forward
• no movement
        Bacterial Respiration
• Obligate aerobes – require oxygen
• Obligate anaerobes – must live in
  absence of oxygen
  – example is Clostridium botulinum
• Facultative anaerobes – can live with or
  without oxygen
                  Reproduction
• Some can reproduce every 20 minutes
• Held in check by food and production of wastes
  Types:
• Binary Fission
• Replication of DNA and division in half
• Asexual
• Conjugation
• Sexual – involves the exchange of genetic material
• Long bridge of protein forms between the cells
• Donor genetic information transferred to recipient
  through bridge
• Recipient cell has different genes at the end than it did
  to begin with
           Importance of Bacteria
•   Used in production of products we use every day
•   Yogurt
•   Cheese
•   Buttermilk
•   Sour cream
•   Pickles
•   Sauerkraut
•   Vinegar
•   Wine
•   Industry
•   digest petroleum
•   remove wastes and poisons from water
•   synthesizing drugs – through genetic engineering
       Symbiotic Relationships
           (mutuallism)
• E. coli in humans – help us digest food –
  make vitamins we can’t, we give them a
  home, food, and transportation
• Bacteria in the intestines of cattle allow
  them to break down cellulose (in grass
  and hay)
   Bacteria in the Environment
• Bacteria are like the stage hands that
  allow the show to go on without being
  seen (or always given the credit)
• Bacteria recycle and decompose dead
  material
• Saprophytes – organisms that use the
  complex molecules of a once living
  organism as their food source
     Sewage decomposition
• Sewage treatment – bacteria is added
  directly to the raw sewage
• How does a septic tank work?
           Nitrogen Fixation
• All organisms are TOTALLY dependent on
  monerans for Nitrogen
• All Plants need nitrogen to make amino acids (-
  NH2)
• Because animals eat plants, they get their
  proteins from plants
• What percentage of the air is Nitrogen?
• Plants, and most other organisms cannot use
  this directly
• Need Nitrogen to be “FIXED” chemically as
  ammonia
             Nitrogen Fixation
• Scientists can make synthetic nitrogen containing
  fertilizers by mixing Nitrogen and Hydrogen gases,
  heating to 500 degrees C and compressing it to 300 X
  normal atmospheric pressure – dangerous, expensive,
  time consuming
• Many cyanobacteria can take nitrogen from the air and
  convert it to a useable form – this is called Nitrogen
  Fixation
• Bacteria are the only organisms that can do this.
• Some plants have a symbiotic relationship with nitrogen
  fixing bacteria
• soybean – Rhizobium grows in nodules around roots
Diseases caused by Viruses and Monerans

• only a small number of viruses and
  bacteria can cause disease
• Pathogens – organisms that cause
  disease
• All viruses infect living cells
• Disease occurs when infection causes
  damage to the cells
          Viruses and Disease
• Examples are:
  –   Small Pox
  –    Polio
  –   Measles
  –   AIDS
  –   Mumps
  –   Influenza
  –   Yellow Fever
  –   Rabies
  –   Common Cold
  –   Ebola etc…
                Vaccine
• The body’s own defenses must be used
• Vaccine – dead or weakened viruses that
  stimulate the bodies defense system
• Symptoms can be treated sometimes, but
  once someone is infected by a virus, there
  is not much science can do
       Bacteria and Disease
• Bacterial diseases include:
  – Diptheria
  – TB
  – Typhoid
  – Tetnus
  – Hansen disease
  – syphilis
  – cholera
  – bubonic plague
  – Flesh Eating Bacteria
 2 ways bacteria cause disease
1. Damage cells and tissues of infected
   organisms directly by breaking down cells
2. Releasing toxins (poisons)
• Many bacteria can live without a host organism
   (on a petri dish)
• Rickettsiae cannot live outside a host cell. They
   have leaky cell walls
• Rickettsiae cause Rocky Mountain Spotted
   Fever, typhus, and Legionnaire’s disease
• Measures to fight bacterial infection
  include:
  – Antibiotics – drugs and natural compounds
    that attack and destroy bacteria in the body
  – NOT Effective against viruses

				
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