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MICROBIOLOGY The Biology of Viruses

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Title: MICROBIOLOGY The Biology of Viruses


1
MICROBIOLOGYThe Biology of Viruses Bacteria
2
VirusesThe Non-Living Microbial World
3
Microbial Size Comparisons
4
Viruses
  • Viruses are nonliving particles
  • Made of nucleic acid, protein, and lipids
  • They are 1000x smaller than bacteria
  • Reproduce only by infecting living cells

5
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.

6
Viral Structure
7
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.

8
Viral Host Range
  • PLANT ANIMAL
    BACTERIOPHAGE
  • Tobacco mosaic Poliomyelitis T4

9
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

10
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.

11
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.

12
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
Go to Section
13
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
14
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.

15
Retroviruses
16
Viruses Disease
  • Viruses cause a variety of human diseases such
    as
  • Polio
  • Measles
  • AIDS
  • Mumps
  • Influenza
  • Common cold

17
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

18
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!

19
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.

20
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

21
ProkaryotesThe Living Microbial World
22
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.

23
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.

24
Bacterial Structure
25
Bacterial Shapes
  • Bacilli rod-shaped prokaryotes
  • Cocci spherical prokaryotes
  • Spirilla spiral or corkscrew shaped prokaryotes

26
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

27
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.

28
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

29
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.

30
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
  • http//highered.mcgraw-hill.com/sites/0072556781/s
    tudent_view0/chapter13/animation_quiz_1.html
  • Transduction
  • http//highered.mcgraw-hill.com/sites/0072556781/s
    tudent_view0/chapter13/animation_quiz_2.html
  • Conjugation
  • http//highered.mcgraw-hill.com/sites/0072556781/s
    tudent_view0/chapter13/animation_quiz_3.html

31
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32
Bacterial Adaptations
  • Binary Fission Conjugation
    Endospore

33
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.

34
Nitrogen Fixation
35
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.

36
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
37
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.

38
Bioremediation
39
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.

40
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!
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