Download Viruses

Mr. Wright, 2011
Section 19.2
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A virus is a nonliving particle made up of
nucleic acid and a protein or lipid-protein coat.
They reproduce, infect, and adapt. So why are
they non-living?
 Cannot move outside of a host.
 Cannot reproduce without the aid of a host.
 Cannot produce their own energy (ATP).
 Not made of cells.
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Spread by air, water, food, bodily fluids, and other
organisms.
Outside of a host cell, viruses have no control
over its movements.
A vector is an intermediate host that transfers a
pathogen or parasite to another organism.
Examples: fleas, mosquitoes, ticks
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Viruses infect all living organisms.
They cause many diseases and are useful
tools for genetic research.
 We’ll talk about why later!
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The study of viruses = virology
There are over 2000 types of viruses.
Viruses are about 100 times smaller than
bacteria.
Viruses come in many different shapes and
sizes.
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Let’s draw one!
A virus is made of 3 parts:
 Genetic Material
 The genome can be either DNA or RNA.
 Protein Coat
 This protein coat is called a capsid.
 Lipid Envelope
 Some viruses have a layer of fat around the
outside.
 Not all viruses have one – useful for
classifying into groups!
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Like living things, it is useful to put viruses
into groups based on several factors.

Is their genetic material DNA or RNA?
 Is it single stranded or double stranded?
 Is it linear or circular?

What is the shape of their capsid?
 Can be helical, spherical, or icosahedral

Does the virus have an envelope?
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A bacteriophage is a special type of virus that
infects bacteria.
They have a very specialized shape.
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Bacteriophages
use these
specialized
shapes to inject
their genome
into bacteria –
it’s kind of like
giving a shot.
Section 19.2
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Viruses are obligate intracellular parasites.
 What do you think that means? (break it
down!)
 Obligate – required
 Intracellular – inside a cell
 Parasite – something that lives off of
something else
Simply put, a virus has to live inside of another
cell in order to reproduce.
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Viruses first need to recognize a host cell before
they can infect it.
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They do this using a “Lock-and-key” method.
The virus has to match up and “fit” a specific cell in
order to infect it – like a key that only fits in one
lock.
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Once a virus has found a host cell, it injects
its genome inside it and the genome forms a
circle.
Viruses need to make 2 parts to reproduce:
 Make new viral proteins (capsids)
 Make new viral genetic material
There are two pathways for viral replication
– the lytic cycle, and the lysogenic cycle.
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The viral genome takes control of the cell,
producing many more viruses. The cell then bursts
(lyses), releasing all new viruses.
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The viral genome combines with the host
genome, where it “hibernates” for
awhile.
Every time the host cell divides, it copies
its genome. Every new cell is infected
with the viral genome.
The virus eventually enters the lytic
cycle.
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Scientists can use viruses for good – we can
inject any gene we want inside of a cell.
As we’ve seen, if a virus goes through the
lysogenic cycle, this new gene combines with
the host cell’s genome.

We’ve just inserted a gene!
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How do we use this? What kind of genes can
we add to organisms?
 Genes that make crops with higher yields.
 Genes that add vitamins and minerals to
food.
 Genes that make livestock grow bigger.
Section 19.3
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Chickenpox
 Symptoms include fever and skin rash.

Itchy boils all over the body.

Spread through direct contact and through
the air.
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Most people get chickenpox as a kid. Once
you’ve had the virus, you develop a lifelong
resistance to that strain!
HOWEVER, the virus can reemerge as you get
older, making you sick again. This is called
shingles. The older you are, the worse it is.
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AKA the flu.
Causes fever, muscle pain, headache,
weakness, and general discomfort.
Spreads through the air and through bodily
fluids.
Mutates very quickly!
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The fact that influenza mutates so fast is what
leads to all the different strains out there.
Examples:
Swine Flu
 Bird Flu/Avian Flu
 Horse Flu
 Dog Flu
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Named after the animals they’re most
commonly found in.
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An emerging disease
is a disease that seems
to come out of
nowhere to reek
havoc in a short
amount of time.
Examples:
Ebola
 West Nile virus
 Any zombie movie
ever.
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Some viruses can lead to cancer.

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Cancer – cells dividing uncontrollably, forms a lump
called a tumor
Example: HPV (Human papillomavirus) 
Cervical Cancer
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AIDS = Acquired Immunodeficiency Syndrome
Caused by HIV.
 HIV = Human Immunodeficiency Virus
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HIV infects the bodies immune system, hurting
the bodies ability to fight other infections.
An opportunistic infection is an infection
caused by something that wouldn’t normally
cause disease in a healthy immune system.
These infections cause serious problems in
AIDS patients, eventually resulting in death.
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HIV can be spread in three ways:
 Sexual contact
 Blood
 From mother to fetus
 Treatments
can slow the
course of the disease, but
there is no cure or vaccine.
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AIDs is a pandemic – there are currently 33.2
million people worldwide with the disease.
Main way to combat AIDs is awareness.
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HIV is a retrovirus.

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A retrovirus is a special type of virus that has RNA
as its genetic material and contains an enzyme called
reverse transcriptase.
Reverse transcriptase transcribes DNA from RNA.
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Viroids
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Viroids are the smallest known particles able to
replicate.
It’s basically a virus without a capsid – just a single
circular strand of RNA.
They infect plants and damage entire crop fields.
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Prions
A prion is basically just
a capsid – a virus
without a genome.
 They convert normal
brain proteins into
other prions.
 As prions accumulate
in a cell they clump
together and lead to cell
death.
 Mad Cow Disease is a
prion disease.
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Solving the Puzzle
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Some viruses, such as influenza
and HIV, mutate very fast.
Fast viral mutations make
treating the viruses difficult,
because they are constantly
changing.
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The immune system begins to target the
original viral strain, but not the new mutant
strain yet.
All of the old strain viruses are destroyed,
while the new strain is unaffected.
The new mutant strain becomes the dominant
strain within the body, then starts to spread.
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Vaccinations
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A vaccine is a solution containing a harmless version
of a virus, bacterium, or a toxin
The immune system learns to recognize and kill
harmful versions.
Vaccinations are highly effective
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Vector Control
What are some examples of a vector?
 An important part of preventing viral disease is the
control of animal vectors.
 If you wipe out what spreads the disease, you wipe
out the disease.
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Drug Therapy
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Would an antibiotic be able to stop a viral disease?
It is difficult to design a drug that stops the virus
without harming the host cells.