Viruses

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Viruses
Viruses

• What are they?
• How do they work?
• Where do they come from?
• And What good are they?

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What is a virus?
An infectious agent made up of a core of
nucleic acid DNA or RNA (ONLY ABOUT 5
GENES) a protein coat (capsid)
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How Big are viruses?
Polio virus 20 nanometers
20nm
1 nm 0ne billionth of a meter! 3000 polio
viruses fit across the diameter of a period at
the end of a sentence in your book.
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Some viruses are naked!They have no envelope
Some viruses have no envelope theyre naked!
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Some viruses have an envelope to cover them!
Envelope came from hosts cell membrane when
virus budded out of host
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Viruses dont reproduce..They Replicate.Once
inside a cell, the cell does all the work and
produces new viruses using the inserted Dna or
Rna as a Guide.
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Lytic Cycle
The lytic cycle
Attachment

• a

injection
Lysis
replication
assembly
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Sometimes the virus doesnt kill the cell right
away and it becomes part of the cells genes.If
this happens, the virus DNA becomes a prophage
and can become activated at any time (like a time
bomb).In the meantime, the prophage is passed on
to all the offspring of that cell . Maybe for
many generations.
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Assembly
lysis
Lytic cycle
Attachment
Replication
Viral dna becomes activated
Integration virus DNA joins cells DNA
Lysogenic cycle
Each daughter cell contains both bacterial and
viral dna
Cells DNA (along with viral dna is replicated
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Are viruses living or nonliving?
What are some characteristics of life? Do
viruses exhibit these characteristics?
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When were viruses discovered?
Viruses have apparently always been
around. However, it wasnt until 1897 that a
Dutch scientist named Beijerinck called an
invisible agent that was smaller than bacteria a
virus (Latin for poison). He was studying
tobacco leaves that had been infected with what
we now know as tobacco mosaic virus.
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Classification of Viruses
By Shape Host type
function
Retroviruses attack a certain way. DNA viruses
attack another way.
Animal viruses
Plant viruses
Bacteria viruses
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Retroviruses
Contain RNA When infecting a cell, these viruses
have to transcribe the RNA to DNA before the
viral code can be read. This requires an enzyme,
reverse transcriptase, to Change RNA to DNA then
the viral code can be added to the cells
DNA. Once part of the cells Dna, the viral code
can cause the cell to make more viruses.
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HIV IS A RETROVIRUS
rna
CAPSID
REVERSE TRANSCRIPTASE
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Nonviral infectious agents

• Prions
• PIECE OF PROTEIN
• CAUSE OF MAD-COW DISEASE
• CAN INFECT ANIMALS INCLUDING HUMANS

• vIROIDS
• Single strand of RNA
• Causes plant diseases

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Human diseases caused by viruses

• Common cold
• Influenza (flu)
• Chickenpox
• Polio
• HIV
• Some pneumonia
• Some meningitis
• herpes

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Viruses in the biosphere

• Animal diseases
• Distemper
• Rabies
• pneumonia

• Plant Diseases
• Discolor leaves
• Stunt growth
• Kill plants

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Uses for viruses

• Vaccines dead or weakened form that stimulates
  the immune system to fight the virus when exposed
  to it.
• Genetic engineering use a virus carrier to
  insert genes into diseased cells.
• Agriculture
• Pest control
• Colorful variations in some plants - flowers

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interesting viruses

• Ebola virus kills quickly requires close
  contact, such as when preparing a body for burial
  or using dirty needles since it kills so fast,
  it generally dies out quickly.

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• Human sarcoma virus
• causes tumors
• Adenovirus causes
• The Common cold

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Bacteriophages infect bacteria very well
studied.
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Smallpox once wiped out entire nations, now a
memory Most successful vaccination program in
world.
Smallpox virus
Arent you glad theres no smallpox anymore?
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Vaccines dead or weakened form of virus
injected to provide immunity.
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First vaccine

• Chinese had been using
• the idea for centuries,
• but didnt market it.
• Dr. Edward Jenner noticed that milkmaids who had
  had cowpox rarely got smallpox.
• Injected a boy with cowpox pus he got cowpox
• When injected with smallpox pus, he did not get
  it!

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The end
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