MICROBIOLOGY The Biology of Viruses

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MICROBIOLOGYThe Biology of Viruses Bacteria
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VirusesThe Non-Living Microbial World
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Microbial Size Comparisons
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Viruses

• Viruses are nonliving particles
• Made of nucleic acid, protein, and lipids
• They are 1000x smaller than bacteria
• Reproduce only by infecting living cells

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Viral Structure

• A virus is a genome enclosed in a protective
  coat.
• Genome is an entire set of genes (DNA or RNA)
• Capsid is the protein coat that encloses the
  viral genome.
• Capsids are built from a large number of protein
  subunits called capsomeres.
• Viral Envelopes accessory structures that help
  viruses infect their host these are membranes
  cloaking the capsid.
• Envelopes are derived from the membrane of the
  host cell.

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Viral Structure
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Viral Host Range

• Most viruses are highly specific to the types of
  cells they infect (referred to as host range)
• Plant viruses infect plants only.
• Animal viruses infect certain species of animals
  only.
• Bacteriophages infect only bacteria.
• Some viruses (like rabies) have a broad enough
  host range to infect several species, while
  others infect only a single species.

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Viral Host Range

• PLANT ANIMAL
  BACTERIOPHAGE
• Tobacco mosaic Poliomyelitis T4

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Viral Reproduction

• Viruses can reproduce ONLY within a HOST cell
  because they lack the enzymes necessary for
  metabolism and the ribosomes necessary for
  protein synthesis.
• They use enzymes, ribosomes, and small molecules
  of host cells to synthesize progeny viruses.
• 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.
• There are basically 5 steps to viral reproduction
• Attachment
• Penetration
• Replication and Synthesis
• Assembly
• Release

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Viral Reproduction

• After entering the cell, the viral DNA uses host
  nucleotides and enzymes to replicate itself.
• The viral DNA uses other host resources to
  produce its capsid proteins by transcription and
  translation.
• The new viral DNA and capsid proteins assemble
  into new virus particles, which leave the cell.

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Types of Viral Infection

• In a lytic infection, a virus enters a cell,
  makes copies of itself, and causes the cell to
  burst.
• The virus takes over the host cell immediately
  and reproduces quickly the host cell can lyse
  within a few minutes (Ex rhinovirus).
• Viruses that reproduce by lytic cycles are called
  virulent viruses.
• 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.
• This hidden DNA is referred to as a provirus or
  prophage.
• Then, because the host cell has reproduced, the
  virus will reproduce and emerge from MULTIPLE
  cells at once, causing much more severe cellular
  damage. Once free from the cell, the phage will
  initiate a lytic cycle (Ex. HIV).
• Viruses that reproduce by both lytic and
  lysogenic cycles are called temperate viruses.

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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 that
can 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
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Retroviruses

• Many viruses, such as HIV, are RNA viruses and
  are therefore referred to as retroviruses.
• RNA is the only nucleic acid found in
  retroviruses.
• These viruses have a complex replication cycle.
• Once inside a host cell, the retrovirus makes DNA
  from its RNA.
• To do this, it uses reverse transcriptase, an
  enzyme that helps produce double-stranded DNA
  from single-stranded RNA.
• The newly made viral DNA is then integrated into
  the host cells chromosome and becomes a provirus.

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Retroviruses
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Viruses Disease

• Viruses cause a variety of human diseases such
  as
• Polio
• Measles
• AIDS
• Mumps
• Influenza
• Common cold

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Treating Viral Infection

• Antibodies are made by hosts immune system after
  infection occurs (if host survives the infection)
• Help inactivate viruses and destroy harmful
  bacteria
• Are specific for viruses or bacteria
• Once an antibody is produced that recognizes a
  specific virus or bacteria, then that strain will
  be ineffective on that individual organism
• Vaccines are harmless variants or derivatives of
  pathogenic microbes
• Stimulate the immune system to mount defenses
  against a specific pathogen
• Developed by Edward Jenner cowpox used to
  develop smallpox vaccination
• Vaccinated or immunized again disease. Ex. MMR,
  DPT, polio, smallpox, influenza, rabies,
  hepatitis C
• Interferons are chemicals in the body that are
  activated when cells are attacked
• Cell under siege produces interferon which binds
  to neighboring cells cell membranes to warn them
  of the dangerous pathogen

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Treating Viral Infection

• 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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Particle/Other Diseases

• Oncogenic viruses generally carry genes that
  disrupt the normal controls over cell growth and
  division.
• Retroviruses are viruses that contain RNA as
  their genetic information (example HIV).
• Prions are particles that contain only protein,
  but no DNA or RNA (example mad cow disease).
  Cause degenerative brain disease.
• Viroids are plant pathogens that consist of a
  short stretch of circular, single-stranded RNA
  without the protein coat that is typical for
  viruses.

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Emerging Viruses

• Emerging viruses that cause new outbreaks of
  disease are usually existing viruses that manage
  to expand their host territory.
• AIDS
• Hantavirus
• Ebola (hemorrhagic fever)
• Nipah virus
• Influenza
• What contributes to spread of emerging viruses?
• Rapid Mutation
• Jumping Expanding Host Range
• Technology World Travel
• Expanding Population Sizes
• International Distribution of Food
• Lifestyle/Cultural Choices

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ProkaryotesThe Living Microbial World
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Prokaryotes

• Microscopic life covers nearly every square
  centimeter of Earth. There are many different
  sizes and shapes of microbes. The smallest and
  most common microbes are prokaryotes.
• Prokaryotes are single-celled microorganisms that
  lack a nucleus and are smaller than most
  Eukaryotes.
• Prokaryotes can be divided into two very
  different groups
• Eubacteria
• Cell walls are made of peptidoglycan (a
  carbohydrate).
• Archaebacteria
• Cell walls lack peptidoglycan.
• DNA sequence resembles that of Eukaryotes.

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Bacterial Genetics

• The major component of the bacterial genome is
  one DOUBLE STRANDED, CIRCULAR DNA molecule which
  is smaller and less complex than that of
  eukaryotes.
• Different from eukaryotic chromosomes which have
  linear DNA molecules associated with large
  amounts of protein.
• Within bacterium, the chromosome is so tightly
  packed that it fills only part of the cell
  dense region called nucleoid NOT bound by
  membrane like the nucleus of eukaryotic cell.
• Replication of DNA occurs from single origin of
  replication on circular DNA and
  transcription/translation can be coupled in
  prokaryotes.
• In addition, many bacteria have PLASMIDS, much
  smaller circles of DNA.
• Each plasmid has only a small number of genes,
  from just a few to several dozen.

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Bacterial Structure
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Bacterial Shapes

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

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Bacterial Structure

• 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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Bacterial Locomotion

• 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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Bacterial Metabolism

• 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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Bacterial Metabolism

• 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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Bacterial Gene Transfer

• Bacteria do not undergo meiosis and fertilization
  as do eukaryotic organisms they reproduce via
  means of genetic recombination
• The genetic recombination in bacteria includes
• Transformation
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• Transduction
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• Conjugation
• http//highered.mcgraw-hill.com/sites/0072556781/s
  tudent_view0/chapter13/animation_quiz_3.html

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Bacterial Adaptations

• Binary Fission Conjugation
  Endospore

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Bacterial Importance

• Bacteria are VITAL to maintaining the living
  world
• As producers, bacteria help to supply the
  atmosphere with oxygen.
• As decomposers, bacteria help the ecosystem
  recycle nutrients
• As recyclers, bacterial also perform critical
  steps in sewage treatment. Bacteria break down
  complex compounds in the sewage into simpler
  ones.
• As nitrogen fixers, bacteria are able to covert
  atmospheric nitrogen into a usable form for plant
  growth.

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Nitrogen Fixation
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Bacteria 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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Bacteria Disease
DISEASE PATHOGEN PREVENTION
Tooth decay Streptococcus mutans Regular dental hygene
Lyme disease Borrelia burgdorferi Protection from tick bites
Tetanus Clostridium tetani Current tetanus vaccination
Tuberculosis Mycobacterium tuberculosis Vaccination
Salmonella Salmonella enteritidis Proper handling of food
Pneumonia Streptococcus pneumoniae Maintaining good health
Cholera Vibrio cholerae Clean water supplies
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Human Uses of Bacteria

• Bacteria are used in the production of a variety
  of food
• Cheese (as starter culture promotes growth)
• Yogurt (turns sugar into milk by fermentation)
• Wine (for fermentation)
• Buttermilk (converts lactose sugar to lactic acid
  to lower pH of milk makes flavor sour)
• Bacteria are used in industry
• Cleaning up oil spills, removal of wastes from
  water, synthesis of drugs.
• The use of bacteria in this way is referred to as
  bioremediation.

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Bioremediation
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Controlling Bacterial Growth

• 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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Controlling Bacterial Growth

• Antibiotics medicines used to prevent bacteria
  from reproducing.
• Antiseptics chemicals such as mouthwash/skin
  creams that kill certain bacteria on contact
  (used on humans).
• Disinfectants chemicals such as Clorox Lysol
  that kill bacteria on surfaces (not used on
  humans).
• Antibodies produced by your body to defend
  against foreign invaders.
• NOTE ANTIBIOTICS ARE NOT USED ON VIRUSES THEY
  ARE USED TO TREAT BACTERIAL INFECTIONS ONLY!