BACTERIA

1
BACTERIA VIRUSES

• Unit VI
• Chapter 19

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Prokaryotes

• Microscopic life covers nearly every square
  centimeter of Earth
• There are many different sizes and shapes of
  microorganisms
• The smallest and most common microorganisms are
  prokaryotes
• Prokaryotes are single-celled microorganisms that
  lack a nucleus and are smaller than most
  Eukaryotes

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Classifying Prokaryotes

• Prokaryotes can be divided into two very
  different groups
• Eubacteria
• Cell walls made of peptidoglycan (a carbohydrate)
• Archaebacteria
• Cell walls lack peptidoglycan
• DNA sequence resembles that of Eukaryotes
• Prokaryotes are identified by their shapes, the
  chemical natures of their cell walls, the ways
  they move, and the ways they obtain energy

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Prokaryotic Shapes

• Bacilli rod-shaped prokaryotes
• Cocci spherical prokaryotes
• Spirilla spiral or corkscrew shaped prokaryotes

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Prokaryotic Cell Walls

• Two different types of cell walls are found in
  eubacteria
• Gram positive absorb violet dye and stain purple
  under a microscope
• Gram negative absorb red dye and stain
  reddish/pink under a microscope

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Prokaryotic Movement

• Most prokaryotes do not move at all, however,
  those that do will use one of three types of
  movement
• Propelled by whip-like flagella
• Lash or spiral forward
• Glide slowly along a layer of slimelike material
  they secrete

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How Prokaryotes Obtain Energy

• Some are autotrophs
• Photoautotrophs carry out photosynthesis
• Chemoautotrophs obtain energy from inorganic
  molecules
• Some are heterotrophs
• Obtain energy by taking in organic molecules and
  then breaking them down
• Photoheterotrophs are photosynthetic but also
  need organic compounds for nutrition

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Oxygen Needs in Prokaryotes

• Obligate Aerobes require a constant supply of
  oxygen in order to live
• Obligate Anaerobes are poisoned by oxygen do
  not require it to live
• Faculative Anaerobes can survive with or without
  oxygen

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Growth Reproduction in Prokaryotes

• Binary Fission a method of reproduction in
  which a prokaryote replicates its DNA and divides
  in half producing 2 identical daughter cells
• Conjugation the transferring of genetic
  information from one prokaryote to another
• Endospore Production the process of producing a
  thick internal wall that allows the prokaryote to
  remain dormant for long periods of time while
  conditions are unfavorable for reproduction

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Growth Reproduction in Prokaryotes

• Binary Fission Conjugation Endospore

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Bacteria in Nature

• Bacteria are vital to maintaining the living
  world
• Some are producers that capture energy by
  photosynthesis
• Others help to break down the nutrients in dead
  matter and the atmosphere, allowing other
  organisms to use the nutrients

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Bacteria as Decomposers

• As decomposers, bacteria help the ecosystem
  recycle nutrients
• The bacteria breaks down the dead matter into
  simpler substances
• As recyclers, bacterial also perform critical
  steps in sewage treatment
• Bacteria break down complex compounds in the
  sewage into simpler ones

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Bacteria as Nitrogen Fixers

• Plants and animals depend on bacteria for
  nitrogen
• Although the Earths atmosphere is approximately
  80 nitrogen gas (N2), plants cannot use that
  nitrogen directly
• The process of converting N2 to a form of
  nitrogen that plants can use (NH3) is called
  nitrogen fixation
• Certain bacteria are the only organisms that can
  fix nitrogen in this way

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Nitrogen Fixation

• Many plants have a symbiotic relationship with
  nitrogen fixing bacteria
• Soybeans and other legumes host the bacterium
  Rhizobium
• Rhizobium grows in nodules that form on the roots
  of the plant
• The plant provides a source of nutrients for
  Rhizobium, which converts nitrogen in the air
  into ammonia, which helps the plant

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Bacteria and Disease

• Bacteria are everywhere in nature, but only a few
  cause disease
• Bacteria that cause disease are called pathogens
• Bacteria can cause disease in one of two ways
• By damaging the tissues of infected organisms as
  they break them down for food
• By releasing toxins that harm the body of the
  organism
• Antibiotics are compounds that block the growth
  and reproduction of bacteria

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Common Diseases Caused by Bacteria
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Human Uses of Bacteria

• Bacteria are used in the production of a variety
  of food
• Cheese, yogurt, wine, buttermilk, etc.
• Bacteria are used in industry
• Cleaning up oil spills, removal of wastes from
  water, synthesis of drugs

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Controlling Bacteria

• Sterilization destroys bacteria by subjecting
  them either to great heat or to chemical action
• Refrigeration causes bacteria to grow more
  slowly
• Preservatives canning prevents bacteria from
  spoiling shelf foods
• Chemical Treatment chemicals (such as salts) can
  prevent the growth of bacteria in food

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Viruses

• Viruses are NONLIVING particles of nucleic acid,
  protein, and lipids that can reproduce only by
  infecting living cells
• A typical virus is composed of a core of either
  DNA or RNA surrounded by a protein coat
• A viruss outer protein coat is called a capsid

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Virus Structures
Tobacco Mosaic Virus
Influenza Virus
T4 Bacteriophage
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Viral Infection

• Most viruses are highly specific to the cells
  they infect
• Plant viruses only infect plants
• Animal viruses only infect certain species of
  animals
• Bacterial viruses (called bacteriophages) only
  infect bacteria

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Lytic v/s Lysogenic Infection

• In a lytic infection, a virus enters a cell,
  makes copies of itself, and causes the cell to
  burst
• In a lysogenic infection, a virus embeds its DNA
  into the DNA of the host cell and is replicated
  along with the host cells DNA

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The Lytic Cycle
Bacteriophage protein coat
Bacteriophage DNA
Bacterial chromosome
Bacteriophage attaches to bacteriums cell wall
Bacteriophage enzyme lyses the bacteriums cell
wall, releasing new bacteriophage particles
thatcan attack other cells.
Bacteriophage injects DNA into bacterium
Bacteriophage proteins and nucleic acids assemble
into complete bacteriophage particles
Bacteriophage takes over bacteriums metabolism,
causing synthesis of new bacteriophage proteins
and nucleic acids
Bacteriophage Bacteriophage DNA Bacteriophage
protein
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The Lysogenic Cycle
Bacteriophage DNA
Bacterial chromosome
Bacteriophage injects DNA into bacterium
Bacteriophage DNA (prophage) can exit the
bacterial chromosome
Lytic Cycle
Lysogenic Cycle
Bacteriophage DNA (prophage) may replicate with
bacterium for many generations
Bacteriophage DNA forms a circle
Bacteriophage enzyme lyses the bacteriums cell
wall, releasing new bacteriophage particles that
can attack other cells
Prophage
Bacteriophage proteins and nucleic acids assemble
into complete bacteriophage particles
Bacteriophage DNA inserts itself into bacterial
chromosome
Go to Section
25
Viruses Disease

• Viruses cause a variety of human diseases such
  as
• Polio
• Measles
• AIDS
• Mumps
• Influenza
• Common cold
• Vaccines, weakened form of a virus, are the best
  way to protect against most viral diseases
• Vaccines must be used before a viral infection
  begins

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Viruses Disease

• Viruses and Cancer
• Oncogenic viruses generally carry genes that
  disrupt the normal controls over cell growth and
  division
• Retroviruses
• These are viruses that contain RNA as their
  genetic information (example HIV)
• Prions
• Particles that contain only protein, but no DNA
  or RNA (example mad cow disease)