Viruses

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Viruses
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What do you think this is?
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What do you Think These Objects are? Are They
Living?
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Prion, Virus, and Viroid

• Viroid pathogen causes disease in a plant.
  Protein but no capsid - RNA
• Prion pathogen made only of a protein. Mutates
  your proteins! No DNA OR RNA

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2. Plant Viruses(viroids)First plant virus to
be identified was the tobaccomosaic virus400
viruses that infect plants, causing as many as
1000 diseasesCan be beneficial - flower color,
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Plant Virus Tobacco Mosiac
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3. Prions Particles composed of proteins and
have no nucleic acids (still infectious)Influence
how proteins fold into their active
shapeExample Mad cow disease (destroys brain
damage).
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Prions(cause mutations in chromosomes or proteins)

• Alzheimer's disease
• Creutzfeldt-Jakob disease
• Down's syndrome
• Fatal familial insomnia
• Gerstmann-Straussler syndrome
• Kuru Leprosy

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Prion crystalline protein structure
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Viroids

• So small No real pictures!

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Viroids Hepatitis D
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Bacteria Vs Virus
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VIRUSES
Virus infectious particle that contains DNA or
RNA surrounded by a protein coat that can only
reproduce in a host cell. Latin for poison.
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Bacteriophage attacking a bacteria!
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History of viruses
Martinus Beijerinck Dutch scientist who said
that disease is caused by tiny particles in
juice. Called them viruses. Latin for
poison. Wendall Stanley isolated crystals of the
tobacco mosic virus. Dmitri Ivanovski for
tobacco mosiac in liquids extracted from
infected plants.
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Are viruses alive? Scientists are still
arguing!!!

• At the boundary of life, between the
  macromolecules (which are not alive) and the
  prokaryotic cells (which are), lie the viruses
  and bacteriophages (phages).
• These twilight creatures are parasites
  responsible for causing many diseases in living
  things (herpes and HIV in humans, for example).
• Viruses are found everywhere.

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• In isolation, viruses and bacteriophages show
  none of the expected signs of life. They do not
  respond to stimuli, they do not grow, they do not
  do any of the things we normally associate with
  life.

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Characteristics of Living Things
Respond to stimulus virus respond when a cell
is near and attaches. Cells Not cells as we
know them Adapt The viruses do mutate to become
stronger but only in a host cell. Reproduces
only in a host cell Energy Uses energy of the
host DNA Yes they do have their own Grow and
develops Only in host Viruses are parasites
that can only perform certain characteristics in
host cells. Host The cell that the virus
attaches and uses their DNA and resources.
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How do They Name Viruses

1. After the disease they cause.
2. After the organ or tissue they attack
3. Today, they are given a genus name ending in the
   word virus. Code numbers are given to similar
   viruses

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PARTS OF A VIRUS

• Viruses consist of a core of nucleic acid, either
  DNA or RNA, and a protective coat of protein
  molecules and sometimes lipids(capsid).

CAPSID Protein coat Surrounding the DNA.
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Why is Capsid Important?

• It is the protein coat around the virus that
  protests its DNA or RNA.
• IT IS WAY THEY ARE SO HARD TO KILL!!!!!!

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How Do Viruses Attack Their Host

• Host - Cell the virus attacks.
• Attaches to the host cell and interlocks with the
  protein of the host cell. Viruses are very
  specific to the cells they attack. This helps in
  the spread of the disease.
• The outside envelope matches the cell that it
  attacks. Viruses are specific!

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Attacking Host
The virus will attach itself to the host cell.
It will then shoot its DNA into the host cell.
The virus is a parasite that uses the host cell
for its energy and reproduction. It is a
little different if it is a bacteria cell or
eukaryotic cell.
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Attacking the host
The size and shape of a virus determines which
cells or host they can attack.
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Virus Attached to Host
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Size and Shape of Viruses

• Viruses come in all shapes sizes. You can only
• see them with a microscope.
• 3 shapes of viruses
• Enveloped round with spikes( flu viruses)
• Helical Long narrow coiled shape( rabies)
• Polyhedral- many sides(foot and mouth disease)

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The different proteins that make up the capsid
determines the shape of the virus.
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Difference between a bacteriophage and a virus

• Bacteriophages attack bacteria (prokaryotes)
• viruses attack eukaryotic cells(have a
  nucleus).
• Viruses and bacteriophages invade cells and use
  the host cell's machinery to synthesize more of
  their own macromolecules.

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• Once inside the host the bacteriophage or virus
  will either go into a Lytic Cycle -
• destroying the host cell during reproduction.
• or
• It will go into a Lysogenic Cycle - a
• parasitic type of partnership with the cell

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Lytic Cycle
In the lytic cycle, the virus takes over the
hosts DNA and grows its own. It grows its own
DNA and new viruses. The virus uses the energy of
the host cell. When it is full, the host cell
explodes and releases new viruses.
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Lysogenic Cycle
The virus COMBINES its DNA with the host DNA
producing a Prophage. The cell is not destroyed.
As new cells are made, it will be the virus and
not host cell. Cell not destroyed.
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The Lytic Cycle
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The Lysogenic Cycle
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4 types of Viruses
Retroviruses Viruses that contain RNA as their
nucleic acid Once inside a host cell, the
retrovirus makes DNA from its RNA Use reverse
transcriptase (enzyme) to do this- located inside
capsid The double-stranded DNA is then inserted
into the host cells chromosome and becomes a
provirus Example HIV (Human Immunodeficiency
Virus) infects white blood cells, which are used
in fighting off infections and disease
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A retrovirus injects the enzyme, reverse
transcriptase into the cell to copy viral RNA
into DNA.
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HIV Virus
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• HIV is a retrovirus injecting the enzyme, reverse
  transcriptase into the cell to copy viral RNA
  into DNA.

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• HIV doesnt target just any cell, it goes right
  for the cells that want to kill it. Helper" T
  cells are HIV's primary target. These cells help
  direct the immune system's response to various
  pathogens.

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• HIV undermines the body's ability to protect
  against disease by depleting T cells thus
  destroying the immune system.
• The virus can infect 10 billion cells a day, yet
  only 1.8 billion can be replaced daily.

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• After many years of a constant battle, the body
  has insufficient numbers of T-Cells to mount an
  immune response against infections. At the point
  when the body is unable to fight off infections,
  a person is said to have the disease AIDS.
• It is not the virus or the disease that
  ultimately kills a person it is the inability to
  fight off something as minor as the common cold.

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Viruses are host specific a protein on the
surface of the virus has a shape that matches a
molecule in the plasma membrane of its host,
allowing the virus to lock onto the host cell.
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How Do Vaccines WorkA vaccine contains a killed
or weakened part of a germ that is responsible
for infection. Because the germ has been killed
or weakened before it is used to make the
vaccine, it can not make the person sick. When a
person receives a vaccine, the body reacts by
making protective substances called "antibodies".
The antibodies are the body's defenders because
they help to kill off the germs that enter the
body. In other words, vaccines expose people
safely to germs, so that they can become
protected from a disease but not come down with
the disease.
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• Jenner was operating on the now widely accepted
  principle that once a person catches a certain
  disease, he or she is immune to it for the rest
  of their life. For example, once you've had the
  chickenpox, it's extremely unlikely that you'll
  ever catch it again. This is because your body,
  when exposed again, will recognize the disease
  and fight it off. The beauty of vaccines is that
  they help the body develop disease-fighting
  abilities without making you sick. Vaccines
  accomplish this amazing feat by tricking the body
  into believing it already has the full-blown
  disease. Here are the steps in this process,
  known as the "immune response"

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• Vaccine-preventable Diseases
• Anthrax
• Cervical Cancer
• Diphtheria
• Hepatitis A
• Hepatitis B
• Haemophilus influenzae type b
• Human Papillomavirus
• Influenza
• Japanese encephalitis
• Lyme disease
• Measles
• Meningococcal
• Monkey pox
• Mumps
• Pneumococcal
• Polio
• Rabies

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• Rotavirus Bird Flu
• Rubella
• Shingles
• Smallpox
• Tetanus
• Typhoid
• Tuberculosis
• Varicella
• Yellow Fever
• Common Cold
• Swine Flu

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• Bacteria Virus
• Organelles DNA
• Kill with antibiotic Reproduces
• Reproduces on own Energy from
• Needs energy host
• Cell Mutates
• Responds hard to kill
• Adapts Capsid
• Grows