Download Viruses - Teacher Note

VIRUSES
INTRODUCTION
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Viruses – Latin for ‘poison’
Viruses are NOT classified as living (they lack
cytoplasm, organelles and a cell membrane)
Viruses cannot carry any metabolic functions
and cannot reproduce on its own
Viruses require a living HOST cell to reproduce
PARTS OF THE VIRUS
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An inner genetic
material (nucleic acid
- DNA or RNA)
Capsid – outer
protein coat
(provides shape and
accounts for 95% of
the virus)
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Some viruses have spikes or a mechanism to
attach to host cells
Scientists classify viruses based on
their unique characteristics,
including:
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size and shape of the capsid
shape and structure of the virus
type(s) of diseases the virus causes
type of genetic material (RNA or DNA)
method of reproduction
Virus Shape and Structure:
There are different shapes for viruses:
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1) Helical (Spiral)
2) Enveloped
3) Phage (many sides with a tail)
LOOKING IN…
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Viruses were first looked at under electron
microscopes
Size Range: 20 nm to 400 nm
1 nm = 1 billionth of a metre (10-9 m)
1 mm = 1 millionth of a metre (10-6 m)
PICTURE THIS…You can fit almost 5000 influenza
viruses on the head of a pin
VIRUS TYPES
There are many virus types
including:
 Retroviruses
 Reoviruses
 Adenoviruses
 Rhabdoviruses
 Orthomyxoviruses, etc.
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Each has a different inner
nucleic acid, coat and
structure
BACTERIOPHAGE
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Special category of
virus
Word means
‘bacteria- eater’ –
they infect and
destroy bacterial cells
Have a unique shape
with a head and tail
region
THE HOST
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Host – the cell on which another organism lives
Host Range – the limited # of host species, tissues or
cells a virus can infect
Ex. Rabies virus – infects rodents, dogs, humans (it
has a broad host range)
Ex. Human Cold Virus – only infects cells of the upper
respiratory tract
Ex. HIV - only infects certain types of white blood
cells (both have a narrow range)
Methods of Reproduction
Incubation period = the time it takes between
when the virus infects a cell and when
symptoms appear (when the virus ruptures the
cell).
There are two types of reproduction/replication:
 The LYTIC cycle
 The LYSOGENIC cycle
Lytic cycle:
 ATTACHMENT & ENTRY
- The virus invades a host cell and injects its genetic
material into the host cell.
  REPLICATION
- The host cell replicates the parts of the virus (synthesis of
proteins and nucleic acids).
  ASSEMBLY:
- New viruses are assembled in the host cell.
  RELEASE:
- The new viruses are released from the infected host cell to
invade new cells
- The host cell is LYSED (bursts open) and dies.
Note: 25-45 min. production of 100s of viruses
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LYTIC CYCLE
LySOGENic cycle:
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 ATTACHMENT & ENTRY
- The virus invades a host cell and injects its genetic
material into the host cell.
 PROVIRUS FORMATION
- The viral DNA is inserted into the host cell’s DNA and is referred
to as a provirus.
 DORMANCY:
- The viral DNA remains dormant (inactive) for a period of time
while replication of the host cell occurs without any harm to it.
- The viral DNA is activated and extracted from the host cell by a
“trigger” or “stimulus”.
- This trigger stimulates the lytic cycle to begin and the infection
and death of the host cell.
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 REPLICATION
- The host cell replicates the parts of the virus (synthesis of
proteins and nucleic acids).
 ASSEMBLY:
- New viruses are assembled in the host cell.
 RELEASE:
- The new viruses are released from the infected host cell to
invade new cells
- The host cell is LYSED (bursts open) and dies.
LYTIC/LYSOGENIC CYCLE
HUMANS AND VIRUSES
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Many common human diseases are caused by
viruses
Viruses attack cells as it reproduces
The destruction of the cells causes the
symptoms of disease
VIRUSES AND CANCER
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Some viruses can cause cancer by adding
specific genes to an infected cell
transforming it into a cancer cell
Virus
Human papillomavirus
Hepatitis B/C
Epstein-Barr virus
Cancer Type
Cervical, skin, etc.
Liver cancer, lymphomas
Burkitt’s lymphoma, Hodgkin’s
lymphoma
ANTIBIOTICS and VACCINES
Antibiotics
- substances inhibiting the growth of some
microorganisms
- They destroy bacteria NOT viruses
 Vaccines
- Liquid preparations of dead or weakened
viral/bacterial cells that stimulate the
body’s immune system to fight and
produce antibodies
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INFLUENZA VIRUS
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Physical/chemical
differences result in flu
types A,B,C
Strains described by
protein coat, isolation
year and location
Destroys cells in upper
respiratory tract so there
is no sweeping of foreign
particles
Symptoms – sore throat,
congested lungs
Human
Immunodeficiency
Virus (HIV)
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Virus that causes AIDS
(Aquired Immunodeficiency
Syndrome)
Retrovirus is transmitted
through variety of bodily
fluids: blood, semen, vaginal
fluid, breast milk
HIV attacks the immune
system
Since 1981, almost 25
million people have died
from AIDS
Other Viral Diseases
Varicella zoster virus:
chickenpox (children)
and shingles (adults)
Poliovirus - Polio
Variola major virus:
smallpox
SARS coronovirus:
Severe Acute
Respiratory Syndrome
(SARS)