Bacteria and Viruses

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Chapter 19

• Bacteria and Viruses

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19-1 Bacteria

• The invention of the microscope opened our eyes
  to the hidden, living world around us
• Microscopic life covers nearly every square
  centimeter of Earth

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Prokaryotes

• The smallest and most common microorganisms
• Unicellular organisms that lack a nucleusand
  membrane bound organelles
• bacteria

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Classifying Prokaryotes

• Until recently, all prokaryotes were placed in a
  single kingdom - monera
• More recently, biologists have begun to
  appreciate that prokaryotes can be divided into
  two very different kingdoms the eubacteriaand
  the archaebacteria

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Eubacteria

• Eubacteria include a wide range of organisms with
  different lifestyles
• Eubacteria live almost everywhere

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Archaebacteria

• Lack the same carbohydrates of eubacteria and
  also have different membrane lipids
• Also, the DNA sequences of key archaebacterial
  genes are more like those of eukaryotes than
  those of eubacteria
• Many archaebacteria live in extremely harsh
  environments

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Identifying Prokaryotes

• Prokaryotes are identified by characteristics
  such as shape, the chemical nature of their cell
  walls, the way they move and the way they obtain
  energy

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Shapes

• Bacilli rod shaped
• Cocci spherical shaped
• Spirilla spiral and corkscrew shaped

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Cell Walls

• Eubacteria have peptigoglycan
• Archaebacteia dont have peptigoglycan

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Movement

• Some bacteria move differently than others

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Metabolic Diversity

• No characteristic of prokaryotes illustrates
  their diversity better than the way they obtain
  energy

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Heterotrophs

• Must take inorganic molecules for both energy and
  a supply of carbon

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Photoheterotrophs

• These organisms are photosynthetic using sunlight
  for energy but they also need to take in organic
  compounds as a carbon source

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Photoautotrophs

• Use light energy to convert carbon dioxide and
  water to carbon compounds and oxygen in a process
  similar to that used by green plants
• Ex.) cyanobacteria (blue-green algae)

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Chemoautotrophs

• Can perform chemosynthesis
• Make organic carbon molecules from carbon dioxide
• Unlike photoautotrophs, however they do not
  require light as a source of energy. Instead
  they use energy directly from chemical reactions

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Releasing Energy

• Like all organisms, bacteria need a constant
  supply of energy
• This energy is released by the process of
  cellular respiration or fermentation or both

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Obligate aerobes

• Require a constant supply of oxygen in order to
  live

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Obligate anaerobes

• Do not require oxygen and if fact may be killed
  by it

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Facultative anaerobes

• Can survive with or without oxygen

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Growth and Reproduction

• Bacteria can grow really fast
• If unlimited space and food were available to a
  single bacterium and if all of its offspring
  divided every 20 minutes in just 48 hours they
  would reach a mass of approximately 4000 times
  the mass of the earth!

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Binary Fission

• When a bacterium has grown so that it has nearly
  doubled in size, it replicates its DNA and
  divides in half producing 2 identical daughter
  cells

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Binary Fission

• Bacterial reproduction, asexual reproduction

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Conjugation

• Many bacteria are also able to exchange genetic
  information by a process called conjugation
• This transfer of genetic information increases
  genetic diversity

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Spore Formation

• When growth conditions become unfavorable, many
  bacteria form structures called spores

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Endospore

• A type of spore formed when a bacterium produces
  a thick internal wall that encloses a thick
  internal wall that encloses its DNA and a portion
  of its cytoplasm

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Endospore
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Importance of Bacteria

• Bacteria are vital to maintaining the living
  world
• Some are producers that capture energy by
  photosynthesis
• Others are decomposers that break down the
  nutrients in dead matter and the atmosphere
• Still other bacteria have human uses

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Decomposers

• As decomposers, bacteria help the ecosystem
  recycle nutrients, therefore maintaining
  equilibrium in the environment

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Nitrogen Fixers

• You may recall that plants need nitrogen to make
  amino acids, the building blocks of protiens
• Nitrogen gas (N2) makes up approximately 78
  percent of Earths atmosphere
• However, plants cant use nitrogen gas directly
• Nitrogen must first be changed chemically to
  ammonia (NH3) or other nitrogen compounds

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Nitrogen fixation

• Process which turns unusable nitrogen gas into
  useful nitrogen containing compounds
• Allows nitrogen atoms to continually cycle
  through the biosphere
• Many plants have symbiotic relationships with
  nitrogen fixing bacteria

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Human Uses of Bacteria

• Used in food and beverage production
• Industries petroleum, water, mining, drugs
• Inside of us (symbiosis)
• E.coli
• Drug research

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19 2 Viruses
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Viruses

• Particles of nucleic acid, protein, and sometimes
  lipids
• Viruses can reproduce only by infecting living
  cells
• A typical virus is composed of a core of DNA or
  RNA surrounded by a protein coat
• Viruses are very small. They can only be seen
  with an electron microscope

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Capsid

• A viruses protein coat
• The capsid proteins of a typical virus bind to
  receptors on the surface of a cell and trick
  the cell into allowing it inside
• Once inside, the viral genes are expressed and
  causes the host cell to make copies of the virus
  and in the process the host cell is destroyed
• Because viruses must bind precisely to proteins
  on the cell surface and then use a hosts genetic
  system, most viruses are highly specific to the
  cells they infect

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Viral Infection

• Once the virus is inside the host cell, two
  different processes may occur

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Lytic Infection

• In a lytic infection, a virus enters a cell,
  makes copies of itself, and causes the cell to
  burst

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A literary approach to lytic virus infections

• In its own way, a lytic virus is similar to a
  desperado in the Old West. First, the outlaw
  eliminates the towns existing authority (host
  cell DNA). Then, the desperado demands to be
  outfitted with new weapons, horses, and riding
  equipment by terrorizing the local people (using
  the host cell to make proteins). Finally, the
  desperado forms a gang that leaves the town to
  attack new communities (the host cell bursts,
  releasing hundreds of virus particles).

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Lysogenic Infection

• In a lysogenic infection, a virus integrates its
  DNA into the DNA of the host cell, and the viral
  genetic information replicates along with the
  host cells DNA
• Unlike lytic viruses, lysogenic viruses do not
  lyse the host cell right away. Instead, a
  lysogenic virus remains inactive for a period of
  time
• Eventually, only one of a number of factors may
  activate the DNA of a prophage which will then
  remove itself from the host cell DNA and direct
  the synthesis of new viruses particles

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Retroviruses

• Viruses that contain RNA as their genetic
  information
• When retroviruses infect a cell, they produce a
  DNA copy of their RNA
• Ex.) Human Immunodeficiency Virus (HIV) and
  Feline leukemia virus

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Viruses and Living Cells

• Viruses must infect a living cell in order to
  grow and reproduce
• They also take advantage of the hosts
  respiration, nutrition and all the other
  functions that occur in living things
• Therefore, viruses are considered to be parasites

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Parasites

• organisms that live on or in a host organism from
  which it obtains nutrients, and it usually does
  harm to the host

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Are viruses alive?
Cells and Viruses Cells and Viruses Cells and Viruses
Characteristic Cell Virus
Structure Cell membrane, cytoplasm eukaryotes also contain nucleus and organelles
Reproduction Independent cell division either asexually or sexually
Genetic Code DNA
Growth and Development Yes in multicellular organisms, cells increase in number and differentiate
Obtain and Use Energy yes
Response to Environment yes
Change Over Time yes
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19 3 Diseases Caused by Bacteria and Viruses

• Bacteria and viruses are everywhere in nature,
  but only a few cause disease

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Pathogens

• Disease causing agents
• All viruses reproduce by infecting living cells,
  and disease results when the infection causes
  harm to the host
• All bacteria require nutrients and energy
  however, disease results when bacteria interfere
  with the hosts ability to obtain enough of
  those elements to function properly

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Bacterial Disease in Humans

• Bacteria produce disease in one of two general
  ways
• Some bacteria damage the cells and tissues of the
  host by breaking down the cells for food
• Other bacteria release toxins that travel
  throughout the body interfering with the normal
  activity of the host

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Preventing Bacterial Disease

• Many bacterial disease can be prevented by
  stimulating the bodies immune system with vaccines

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Vaccine

• A preparation of weakened or killed pathogen
• When injected into the body, a vaccine sometimes
  prompts the body to produce immunity to the
  disease
• If a bacterial infection does occur, a number of
  drugs can be used to attack and destroy the
  invading bacteria

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Antibiotics

• Compounds that block the growth and reproduction
  of bacteria NOT virus

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Controlling Bacteria

• There are various methods used to control
  bacterial growth, including sterilization,
  disinfectants, and food processing

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Sterilization by Heat

• Many bacteria cannot survive high temperatures
  for a long time, so most can be killed by
  exposure to high heat
• Ex.) pasteurization

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Disinfectants

• Chemical solutions that kill pathogenic bacteria
  (chlorine)

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Food Storage and Processing

• Food that is stored at a low temperature will
  stay fresh longer because bacteria cannot
  reproduce fast at cold temperatures
• Also, a lot of the processing procedures that are
  used in the food industry raise the temperature
  of food to a point where the bacteria are killed

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Viral Disease in Humans

• Like bacteria, viruses produce disease by
  disrupting the bodys normal equilibrium
• Unlike bacterial diseases, viruses cant be
  treated with antibiotics
• The best way to protect against most viral
  diseases lies in prevention by the use of vaccines

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Viral Disease in Animals

• Viruses produce serious animal diseases Ex.)
  Foot-and-mouth disease, Rous sarcoma

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Viral Disease in Plants

• Many viruses infect plants
• Ex.) Tobacco mosaic virus, potato yellow dwarf
  virus

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Viroids and Prions

• Scientists have discovered two virus-like
  particles that also cause disease

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Viroids

• Single stranded RNA molecules that have no
  surrounding capsid
• Cause disease in plants

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Prions

• Proteins that cause disease in animals
• Ex.) Mad cow disease

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