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Viruses
Living or Not
???????
Tonight’s HWK
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Watch HOUSE – Smallpox episode 
Read Section 19-2 and Complete GR
(Remind me at end of class to pass back stuff and
a reminder to all of you to hand in your lab duotangs by 3:30)
*See me after class if you had any issues with
your weekend assignments
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Viruses
Virus – Latin for “_Poison__”
Russian Biologist Dmitri Ivanovski (1892) –
Tobacco Mosaic Disease…not determined to be
a virus until 1930…known as the first virus to
be discovered!~
Characteristics of Viruses
Scientist that studies viruses is called a virologist!
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Among the smallest
biological particles (not
cells) that are capable of
causing harm in living
organisms.
Virus particles are called
virions
5000 influenza viruses
can fit inside the head of
a pin!
Studying the “T4-Bacteriophage
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Also known as: “eaters of bacteria” have a head
and tail region – (serve as the principle
experimental object in studying viruses)
Why study it?
VIRUSES & CELLS
Characteristic
VIRUS
Structure
DNA or RNA core, capsid
Reproduction
Only within a host
Genetic Code
DNA or RNA
Growth/Dvpmt
NO
Energy
NO
Response to Environment No
Change over time
Yes
CELL
Not Considered Living
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A virus is not a bacteria,
fungus, protist, plant or
animal.
They do not carry out
cellular functions.
They do not grow or
undergo division
A virus can not
replicate on their own
– they need to infect a
HOST and use the hosts
organelles and enzymes
to do this!
Viruses - Disease
Viral infections generally behave in 2 ways:
1. Viruses reproduce and cause disease
immediately (lytic or active)
2. Viruses integrate into the host cell (lysogenic
or dormant)
Viral Replication – Lytic Cycle
Infection
See clip on desktop!!
Lytic (kills cells dead)
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Adsorption – (aka attachment) chemical attraction between
the tail fibers and receptor proteins on the host cell (lock & key
fit)
Entry – release an enzyme to weaken the wall of bacterium &
tail sheath contracts forcing a tube in. (like a needle)
Replication – enzymes degrate host DNA and stops making
its molecules and begins using the viruses genome to make
copies
Assembly – proteins spontaneously attach together
Release - The newly assembled viruses are released from the
host bacterial cell as the enzyme completes its degradation of
the cell wall and the bacteria disintegrates.
LYSOGENIC
CYCLE
See clip on desktop!!!
Viral Replication – Lysogenic
Cycle Infection
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The host cell makes copies of the virus indefinately
The virus integrates its DNA into the DNA of the
host cell, and the viral genetic information
replicates along with the host cell’s DNA.
Unlike lytic viruses, lysogenic viruses DO NOT
lyse the host cell right away. (it can remain inactive
for a long period of time)
The viral DNA embedded in the host’s DNA is
called a prophage and it can remain in the host for
many years before becoming active.
What Organisms and Host Cells Do
Viruses Infect?
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Infection by viruses
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viruses infect bacteria, plants, animals and other living
organisms in order to reproduce
a given virus usually infects a limited number of species.
within a host organism, usually only a limited number of cell
types are susceptible to infection by a given virus
Host range
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array of host cells that a particular virus can infect
determined by a “lock-and-key” fit between the virus and a
receptor on the surface of a host cell
Ex: one type of herpes virus causes cold sore, a different one
causes genital sores!
How are Viruses Studied?
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Virology is the study of viruses; scientists who
study viruses are called ___________
What are Viruses made of?
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Viruses are composed of nucleic acid, proteins and
sometimes lipids. They are not very complex!
The Nucleic acid core, which can be either DNA or
RNA, encodes the genetic information to make virus
copies.
The nucleic acid is surrounded by a protective protein
coat called a capsid. These are “Naked” viruses.
An outer membranous layer, called an envelope, made
of lipid and protein, surrounds the capsid in some
viruses…these are called “enveloped viruses”
Virus Structure
Envelope
Nucleic acid
Capsid
How are Viruses Classified?
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Genetic Material
 DNA or
 RNA (retrovirus/mutates
frequently)
 But not both
Capsid (Protein) Structure (95%
of virus)
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Helical (rod shaped)
Polyhedral (spherical)
Complex
Helical Marburg
virus
Polyhedral SV40 virus
Presence or absence of a
membranous envelope
surrounding the capsid
**No envelope = naked virus
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Complex bacteriophage
Host Range
•HIV, for example, only will enter cells that have a surface
protein molecule called CD4. These molecules are found only
on white blood cells. Thus, HIV will only infect white blood
cells and not lung cells or other cell types.
•Sometimes, a virus can mutate and change its host range.
This appears to be happening with the avian flu virus (influenza
A/H5N1) currently circulating. At first, the flu virus could
infect only birds, but changes in the virus genome have
allowed it to infect humans. So now, its host range has
expanded. The change in host range of a virus can be one factor
in the emergence of a new disease.
What Diseases are Caused by
Viruses?
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Infectious diseases
RNA viruses (retroviruses)
DNA viruses
AIDS
Respiratory Disease
Influenza (flu)
Smallpox
Common cold
Chickenpox
Polio
Mononucleosis
Measles
Cold Sores
Tumor Viruses – cause Cancer ex: HPV
How Can Viral Diseases Be
Prevented and Treated?
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Good hygiene
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Vaccines
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Avoid contact with contaminated food, water, fecal material or body
fluids.
Wash hands frequently.
Stimulate natural defenses with in the body.
Contain a component of or a weakened or killed virus particles.
Are developed for many once common illnesses such as smallpox, polio,
mumps, chicken pox.
Not available for all viruses.
Anti-viral drugs (but not antibiotics)
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Available for only a few viruses.
Inhibit some virus development and/or relieve symptoms.
How Do New Viruses Emerge?
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Through mutation and evolution of genetic
code…changes to the protein coat therefore
changing the “lock and key” fit! And no longer
recognizable to a host’s immune system!
Human population expanding into previously
uninhabited areas (increased contact between
humans and animals)
Through the detection of previously
unrecognized viruses
How do our bodies fight viruses?
Functions of the Immune System:
Recognition:
 Antibodies (proteins that bind to the surface of a virus)
recognize an infected cell and attach.
Destruction:
 Leukocytes move in to destroy the infected cells
 Also known as White Blood Cells that come from the bone
marrow
 Goal is to recognize foreign substances (not healthy cells)
Memory:
 Once infected, memory cells recognize the virus if it enters the
cell again!
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HSV1 vs HSV2
Human Papilloma Virus – 14yo boy
http://www.youtube.com/watch?v=6E1zh6ukc
OU
Polio Virus
Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating
Practice Quiz…Have you been
reviewing your notes??
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Real Deal tomorrow…then we start Bacteria!!!
#1-10 on a piece of paper
VIRUS MINI QUIZ
THE PRIMARY FUNCTION OF
ALL VIRUSES IS TO
REPLICATE!!
1.
MINI QUIZ…
2. WHAT IS THE
TYPICAL/COMMON VIRUS THAT
STUDENTS STUDY WHEN
LEARNING ABOUT VIRUSES?
T4 Bacteriophage
MINI QUIZ…
IN ORDER FOR A VIRUS TO
REPLICATE IT NEEDS TO BE IN
A….
HOST CELL
3.
MINI QUIZ…
4. VIRAL REPRODUCTION THAT
KILLS THE HOST CELL IS
CALLED THE
Lytic CYCLE!
MINI QUIZ…
5. WHEN VIRAL DNA IS EMBEDDED
INTO A HOST CELL’S DNA IT
FORMS A….
PROPHAGE
MINI QUIZ…
ANOTHER NAME FOR
INFLUENZA IS….
FLU VIRUS
6.
MINI QUIZ…
7. 3 WAYS VIRUSES CAN BE
TREATED/PREVENTED ARE….
1. Hygiene
2. Vaccines
3. AntiVirals
MINI QUIZ…
8. SCIENTISTS THAT STUDY
VIRUSES ARE CALLED
VIROLOGISTS
MINI QUIZ…
9.
2 WAYS THAT VIRUSES CAN BE
TRANSMITTED ARE….
-- droplets in the air
-- via food or water
-- via mosquitoes, ticks other animals
-- physical contact
MINI QUIZ…
A VIRUS THAT HAS ONLY A CAPSID
SURROUNDING IT’S GENETIC
INFORMATION AND NO ENVELOPE IS
CALLED A….
NAKED VIRUS.
10.