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Viruses
Obj:
n Why no kingdom for viruses?
n Know basic viral anatomy; especially HIV & bacteriophage
n Know stages of 2 life cycles
n Harmful and beneficial effects
n Know several examples of treatments
Virus Introduction
I. General info:
A. 
B. 
C. 
D. 
Pathogens (cause diseases) in all 6
kingdoms.
Virulence is a term used to refer to the
relative ability to do harm or damage to
a host.
Epidemic – a widespread outbreak of
an infectious disease at a specific time.
Pandemic – a worldwide or multiple
continent outbreak of an infectious
disease.
D. 
Doesn’t belong to a kingdom because they
are not considered to be alive.
1. 
They need to invade or infect a host cell
to reproduce
2. 
They do not carry out the most basic
metabolic processes, like using or
producing energy, no wastes.
3. 
They don’t really have any working parts:
i.e. no nucleus, mitochondria, ribosome's
and some even lack cytoplasm.
II. Viral Structure
A. 
B. 
All viruses are small, only visible through
electron microscope
Consist of two parts:
1.  Nucleic acid core.
2.  Outer protein coat called a “capsid”.
a)  Protein coat determines the shape of the virus.
b)  Some viruses (animal) have membranous outer
envelope instead of/or on top of a protein coat
C. Three basic shapes:
1. 
Polyhedral Virons – This shape group
includes the classic virus shape that looks like
a dodecahedron. A dodecahedron is a
geometric shape with twelve (12) sides. e.g.
2. 
Adenovirus (respiratory virus) or HIV.
Spiral (helical)- They are set up like a tube.
The protein coat winds up like a garden hose
around the core. e.g. tobacco mosaic virus
3. 
Complex virons - geometric head and long
legs. e.g. bacteriophage
Receptor proteins
Reverse transcriptase
Protein coat
RNA
Envelope
IV. Two Types of Viral Infection
Pathways: (page 481)
A. 
Lytic Infection (about 25 minutes)
1. 
Attachment -virus attaches itself to the receptor
site of host cell.
a) Viruses are very specific about their host.
b) In some cases the virus is engulfed by the host
cell.
2. 
Injection -virus use enzymes to enter the cell wall of
host and its nucleic acid is injected into the host
cell.
3. 
Replication - host’s DNA disintegrates and viral DNA
or RNA takes over the host cell.
3. Replication continued
a) 
Host cell replicates (copies) viral nucleic acids,
coat proteins, and viral enzymes.
b) 
RNA viruses (retroviruses) have special reverse
transcriptase enzyme to change its RNA into
DNA.
4. 
Assembly -Viral parts are put together to form new
complete viral units.
5. 
Release or Lysis -New viruses release enzymes to
break down host’s cell wall (killing the host cell)
and they are released to invade other host cells.
a) 
Some animal viruses bud off new viral particles.
Lytic Cycle Movie
B. Lysogenic (Prophage)
Cycle (pg 481)
1. 
2. 
3. 
4. 
5. 
Attachment - Same as Lytic
Injection- Same as Lytic
Splicing - The viral DNA is spliced into the
DNA of the host.
Cellular Duplication - During normal cell
division the viral DNA is also duplicated and
passed on with the cell’s own DNA
Activation - An environmental stress
stimulates the activation of the viral DNA
and stages 3-5 of the lytic cycle begin
Harmful Effects of viruses
Route
Skin contact
Respiratory
Fecal-oral
Milk
Transplacental
Sexually
Insect vector
Animal bite
Examples
HPV- Human papilloma virus (warts)
Cold viruses, influenza, measles, mumps, rubella
Polio, echo, Coxsackie, Hepatitis A, Rotavirus
HIV, HTLV-1, CMV
Rubella, CMV, HIV
Herpes 1 and 2, HIV, HPV, Hepatitis B
Yellow fever, Dengue fever, Zika
Rabies
CMV -
cytomegalovirus, HPV, HTLV – Human
T-Lymphotropic virus
disorders
Chicken Pox
Mumps
Measles
Beneficial Effects of viruses
A. 
Can be used to insert desirable
genetic information into cells.
1. 
2. 
B. 
Genetically engineered organisms like tulip
coloration
Deliver correct genes into human cells.
Possible antibiotic (kills bacteria)
VI. Combating Viral Infections?
A. 
B. 
Antiviral Drugs:
1. 
AZT (HIV), Acyclovir (herpes), or Vidarabine
(encephalitis) treat the immediate symptoms, but are
not a cure
Vaccine
1. 
Make a virus less harmful (virulent):
a.  Grow in different host cell, e.g. flu vaccines are grown in
chicken eggs so the flu virus will look for chicken cells instead
of human cells.
b.  Find a less harmful, but similar looking virus, e.g. cow pox vs
small pox.
c.  Chemically alter or destroy the nucleic acid of the virus, e.g.
polio virus was treated with formaldehyde.
B.  Vaccine continued
2. 
Leave some of the viruses outer coat intact. Why?
n 
3. 
4. 
5. 
So our immune system will react to it.
Inject vaccine
A person’s immune system reacts to the less
harmful virus and forms memory white blood cells
(WBC’s).
When you get exposed to the virulent form of the
virus your immune system responds so quickly
that you won’t get sick or your sickness is less
then a non-immunized person would experience.
How We Conquered Smallpox