Bacteria and Viruses

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Bacteriaand Viruses
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Prokaryotes or Bacteria

• Prokaryotes were the earliest organisms on Earth
  and are thought to have evolved alone for 1.5
  billion years.
• Today, prokaryotes still dominate the biosphere.
• biomass outweighs all eukaryotes combined by at
  least tenfold.
• There are more prokaryotes in a handful of
  fertile soil or the mouth or skin of a human than
  the total number of people who have ever lived.
  WOW!!!!!
• Prokaryotes thrive in places that are too hot,
  cold, acidic, or alkaline for other life forms.
  They are the ultimate survivors.

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Bacteria Cont

• Just like the news, we only seem to hear the bad.
  This is the minority!!!!
• During the 14th century, a bacterial disease
  known as bubonic plague, spread across Europe
  and killed about 25 of the human population.
• Other types of diseases caused by bacteria
  include tuberculosis, cholera, many sexually
  transmissible diseases, and certain types of food
  poisoning
• Most bacteria are benign or beneficial.
• Bacteria in our intestines produce important
  vitamins.
• Prokaryotes recycle carbon and other chemical
  elements between organic matter and the soil and
  atmosphere. They produce our insulin, and helps
  us make various foods and alcohol!!!! BIG
  BUSINESS

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Cont

• Prokaryotes often live in close association among
  themselves and with eukaryotes in symbiotic
  relationships. Like in the case of the
  mitochondria and chloroplasts.
• About 5,000 species of prokaryotes are known, but
  estimates of actual prokaryotic diversity range
  from about 400,000 to 4 million species.
• Two main branches of prokaryotes are the bacteria
  and the archaea.
• archaea inhabit extreme environments and differ
  from bacteria in many key structural,
  biochemical, and physiological characteristics

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Size and Shape

• Most prokaryotes are unicellular, but some
  species may aggregate and form colonies that work
  together.
• most common shapes among prokaryotes are spheres
  (cocci), rods (bacilli),and helices or spiral
• Most have diameters in the range of 1-5 um,
  compared to 10-100 ?m for most eukaryotic cells.
• However, the largest prokaryote discovered so far
  has a diameter of 0.75 mm.
• It is a sulfur-metabolizingmarine bacterium
  fromcoastal sediments offNamibia.

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Make Up

• Most bacteria have a cell wall made with
  peptidoglycan, polymer of modified sugars
  cross-linked by short polypeptides.
• Archaea have no cell wall
• The cell walls differ in their make up (Gram
  Stain tells the tale)

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Gram Stain Positive Purple and Negative Red.
Neg. More dangerous and resist antibiotics better.
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How antibiotics work.

• Many antibiotics, including penicillins, inhibit
  the synthesis of cross-links in peptidoglycans,
  preventing the formation of a functional wall,
  particularly in gram-positive species.
• These drugs are a very selective treatment
  because they cripple many species of bacteria
  without affecting humans and other eukaryotes,
  which do not synthesize peptidoglycans.

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Movement and Protections

• Many prokaryotes secrete another sticky
  protective layer, the capsule. It provides
  protections and sticks the bacteria to surfaces.
• Another way to stick is pili, short hair like
  fibers. Aid in conjugations, where bacteria swap
  DNA

• half of all prokaryotes are capable of
  directional movement.

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Movement Cont Cool

• Flagella, whip, is the most common method of
  movement.
• The flagella of prokaryotes differ in structure
  and function from those of eukaryotes.

Rotation of the filament is driven by the
diffusion of protons into the cell through the
basal apparatus after the protons have been
actively transported by proton pumps in the
plasma membrane
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Controlled Movement????

• many prokaryotes are capable of taxis, movement
  toward or away from a stimulus.
• With chemotaxis, binding between receptor cells
  on the surface and specific substances results in
  movement toward the source, chemical in nature.
  (positive chemotaxis) or away (negative
  chemotaxis).
• Other prokaryotes can detect the presence of
  light (phototaxis) or magnetic fields.

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Organization

• lack a nucleus enclosed by membranes.
• lack the other internal compartments bounded by
  membranes that are characteristic of eukaryotes.
• used infolded regions of the plasma membrane to
  perform many metabolic functions, including
  cellular respiration and photosynthesis.

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Cont..

• prokaryotes have only about one-thousandth as
  much DNA as a eukaryote concentrated as a snarl
  of fibers in the nucleoid region.
• double-stranded DNA molecule in the form of a
  ring. also have smaller rings of DNA, plasmids,
  that consist of only a few genes
• They can live without plasmids but plasmids
  provide the cell genes for resistance to
  antibiotics, for metabolism of unusual nutrients,
  and other special contingencies.
• Plasmids replicate independently of the
  chromosome and can be transferred between
  partners during conjugation.

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Reproduction

• reproduce only asexually via binary fission,
  synthesizing DNA almost continuously
• lacking meiosis and sex as seen in eukarotes,
  prokaryotes have several mechanisms to combine
  genes between individuals.
• In transformation, a cell can absorb and
  integrate fragments of DNA from their
  environment.
• This allows considerable genetic transfer between
  prokaryotes, even across species lines.
• In conjugation, one cell directly transfers genes
  to another cell.
• In transduction, viruses transfer genes between
  prokaryotes.

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Growth

• The word growth as applied to prokaryotes refers
  to multiplication of cells and population
  increases, rather than enlargement of individual
  cells.
• Conditions for optimal growth vary according to
  species.
• Variables include temperature, pH, salt
  concentrations, nutrient sources, among others.
• Grown exponentially, with generation time ranging
  from 1-3 hours down to 20 min.
• growth in the laboratory and in nature is usually
  checked at some point.
• The cells may exhaust some nutrient.
• Alternatively, the colony poisons itself with an
  accumulation of metabolic waste.

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The endospore survival trick This is why anthrax
is a good bioweapon.

• Some bacteria form resistant cells, endospores.
• In an endospore, a cell replicates its chromosome
  and surrounds one chromosome with a durable wall
• endospore is resistant to all sort of trauma.
• Endospores can survive lack of nutrients and
  water, extreme heat or cold, and most poisons.
• Sterilization in an autoclave kills even
  endospores by heating them to 120oC.
• Endospores may be dormant for centuries or more.
• When the environment becomes more hospitable, the
  endospore absorbs water and resumes growth.

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Anthrax Endospore
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How They Get Energy

• Species that use light energy are phototrophs.
• Species that obtain energy from chemicals in
  their environment are chemotrophs.
• Organisms that need only CO2 as a carbon source
  are autotrophs.
• Organisms that require at least one organic
  nutrient as a carbon source are heterotrophs.

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Nitrogen Cycle and Oxygen Use

• Prokaryotes are responsible for the key steps in
  the cycling of nitrogen through ecosystems
• During nitrogen fixation, they convert N2 to
  NH4, making atmospheric nitrogen available to
  other organisms for incorporation into organic
  molecules
• oxygen has a positive impact on the growth of
  some prokaryotes and a negative impact on the
  growth of others.
• Obligate aerobes require O2 for cellular
  respiration.
• Facultative anerobes will use O2 if present but
  can also grow by fermentation in an anaerobic
  environment.
• Obligate anaerobes are poisoned by O2 and use
  either fermentation or anaerobic respiration.

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Archaea Extremophiles

• Archaea have at least as much in common with
  eukaryotes as with bacteria
• ability to live where no other life can
• archaea can be classified into methanogens,
  extreme halophiles, and extreme thermophilies.
• Methanogens obtain energy by using CO2 to oxidize
  H2 replacing methane as a waste.
• are strict anaerobes, that live in swamps and
  marshes where other microbes have consumed all
  the oxygen.
• important decomposers in sewage treatment.
• Others live in the anaerobic guts of herbivorous
  animals, playing an important role in their
  nutrition.
• may contribute to the greenhouse effect, by
  producing methane.

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Halophiles Love salt

• Extreme halophiles live in such saline places as
  the Great Salt Lake and the Dead Sea.
• Some just tolerate elevated salinity others
  require an extremely salty environment to grow.
• Colonies of halophiles form a purple-red scum
  from bacteriorhodopsin, a photosynthetic
  pigment very similar to the visual pigment in
  the human retina.

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Some Like It Hot!!!

• Extreme thermophiles thrive in hot environments.
• The optimum temperatures for most thermophiles
  are 60oC-80oC.
• Sulfolobus oxidizes sulfur in hot sulfur springs
  in Yellowstone National Park.
• Another sulfur-metabolizing thermophile lives at
  105oC water near deep-sea hydrothermal vents.

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Comparison
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Are Bacteria Good or Bad?

• If it were not for decomposers, especially
  prokaryotes, carbon, nitrogen, and other elements
  essential for life would become locked in the
  organic molecules of corpses and waste products.
• Humans also use bacteria as metabolic factories
  for commercial products.
• The chemical industry produces acetone, butanol,
  and other products from bacteria.
• The pharmaceutical industry cultures bacteria to
  produce vitamins, Insulin, and antibiotics.
• The food industry used bacteria to convert milk
  to yogurt and various kinds of cheese. BEER,WINE
  LICQUOR, all from bacteria. Some people love
  bacteria!!!!

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Cont

• Soil bacteria, called pseudomonads, have been
  developed to decompose petroleum products at the
  site of oil spills or to decompose pesticides

• More than half of our antibiotics (such as
  streptomycin and tetracycline) come from the soil
  bacteria Streptomyces.

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Some Cause Disease Pathogens

• pneumonia caused by Haemophilus influenzae
  bacteria
• Exotoxins are proteins secreted by prokaryotes.
• Exotoxins can produce disease symptoms even if
  the prokaryote is not present.
• Clostridium botulinum, which grows anaerobically
  in improperly canned foods, produces an exotoxin
  that causes botulism.
• An exotoxin produced by Vibrio cholerae causes
  cholera, a serious disease characterized by
  severe diarrhea.
• Even strains of E. coli can be a source of
  exotoxins, causing travelers diarrhea.

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More Bad Guys

• Salmonella typhi causes typhoid fever.
• Other Salmonella species, including some that are
  common in poultry, cause food poisoning
• Bacteria Evolve Quickly We are responsible for
  super bacteria like MRSA.
• Yersinia pestis- Plague Killed 25 of World
• Treponema pallidum- Syphilis
• Rickettsia rickettsii- Rocky Mountain spotted
  fever (spread by ticks
• Ect..

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Virus

• ? Are viruses alive. This question is till argued
  today. DISCUSS
• What is it A virus is simply segments of DNA or
  RNA depending on the virus wrapped in a protein
  coat.
• Viral genomes may consist of double-stranded DNA,
  single-stranded DNA, double-stranded RNA, or
  single-stranded RNA, depending on the specific
  type of virus, smallest viruses have only four
  genes, while the largest have several hundred
• Size they are smaller then prokaryotes ranging
  in size from 20 to 250nm.Most can only be seen
  with an electron microscope.

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Cont.

• What do they do Viruses are pathogens, or agents
  that cause disease. They replicate by hijacking a
  cells production machinery.
• Are they Alive They do not grow, do not maintain
  an internal environment or homeostasis, they can
  not reproduce on their own, and can not carry out
  any form of metabolism like the Krebs or Calvin
  cycle. They Just exist. Based on the
  characteristics we, biologists, set for something
  to be living they are not alive.
• Discovery 1st discovered in 1935 by Wendell
  Stanley while trying to discover the causes of
  tobacco mosaic disease, which stunts the growth
  of tobacco plants. Through several procedures
  that we don not have time to discuss scientists
  discovered tobacco mosaic virus. Virus is Latin
  for poison

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Look
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Cont

• Structure The protein coat of a virus is called
  a capsid. It contains either DNA or RNA. Aids is
  an RNA virus. Many viruses like the flu,
  influenza, have a membrane around the capsid
  called an envelope made of lipids or
  glycoprotein, proteins attached carbohydrate
  molecules that come from the host cell.
• Shape Have a variety of shapes Spherical,
  helical, and polyhedral, 20 triangular faces and
  12 corners. Those that attack bacteria, called
  bacteriophages, have a tripod like structure.
• Replication Either Lytic or Lysogenic. Get
  inside, viral DNA or RNA incorporates into the
  host DNA and divides. Provirus- where the viral
  gene is inserted into the host cells chromosome.
• Fact 22 mill died of flu in 1918 and 1919.

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Obligate intracellular parasites
reproduce only within a host cell. An isolated
virus is unable to reproduce - or do anything
else, except infect an appropriate host. lack the
enzymes for metabolism or ribosomes for protein
synthesis Viruses identify host cells by a
lock-and-key EXPLAIN
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Specific Made for Each Other

• Some viruses (like the rabies virus) have a broad
  enough host range to infect several species,
  while others infect only a single species.
• Most viruses of eukaryotes attack specific
  tissues.
• Human cold viruses infect only the cells lining
  the upper respiratory tract.
• The AIDS virus binds only to certain white blood
  cells macrophage and T-Cell populations due to
  their receptor sites CD4 and CCR5 Docks with CD4
  cell surface receptor and must also activate the
  CCR5 receptor that turns on endocytosis. 1
  immune to AIDS due to misshaped receptors.

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Viroids and Prions?? Even Simpler

• Viroids, smaller and simpler than even viruses,
  consist of tiny molecules of naked circular RNA
  that infect plants.
• Their several hundred nucleotides do not encode
  for proteins but can be replicated by the hosts
  cellular enzymes.
• These RNA molecules can disrupt plant metabolism
  and stunt plant growth, perhaps by causing errors
  in the regulatory systems that control plant
  growth
• Prions are infectious proteins that spread a
  disease..
• According to the leading hypothesis, a prion is a
  misfolded form of a normal brain protein.
• It can then convert a normal protein into the
  prion version, creating a chain reaction that
  increases their numbers.

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References

• Jack Brown M.S. Biology
• Microsoft Encarta Encyclopedia 2004
• Starr and Taggart The Unity and Diversity of
  Life 10th edition 2004 Thomson Brookes/Cole
• Campbell and Reece Biology 6th edition 2002
  Benjamin Cummings.
• Raven and Johnson Holt Biology 2004 Holt,
  Rinehart and Winston.