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Viruses
Living or Not
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Viruses
Virus – Latin for “_Poison__”
TMV - 1930
Characteristics of Viruses
Science of Viruses – Virology!
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)
Check out:
http://www.cellsalive.com/ph
age.htm
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!
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 called “naked” viruses.
An outer membranous layer, called an envelope, made of lipid
and protein, surrounds the capsid in some viruses…..these ones
are called “enveloped viruses”
The capsid accounts for 95% of the total virus, and gives
the virus a particular shape
Virus Structure
Envelope
Nucleic acid
Capsid
How are Viruses Classified?
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Genetic Material
 DNA or
 RNA
 But not both
Capsid Structure
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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
Complex bacteriophage
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
Mem. e.O
History of Viruses
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Invasions, wars, and immigration can
introduce viral diseases to different populations
Some viral infections have had major global
effects:
Influenza type A is believed to be responsible for
global flu outbreaks in 1918, 1957 and 1968
 16th century Spanish explorers brought small pox,
measles and influenza viruses to the New World
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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!!
LYSOGENIC
CYCLE
See clip on desktop!!!
Viral Replication – Lysogenic Cycle
Infection
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The host cell makes copies of the virus indefinitely
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 period
of time)
The viral DNA embedded in the host’s DNA is called a
prophage and it can remain in the host cell for many…
generations before becoming activated
What organisms and Host cells do
Viruses Infect?
INFECTION BY A VIRUS:
 Viruses infect bacteria, plants, animals and other living
organisms in order to reproduce.
 Narrow host range. Ex: smallpox is only capable of
infecting humans and no other species.
 Viruses are cell specific. Ex: viruses that cause
respiratory disease usually infect cells only in the
respiratory tract.
 Determined by a lock-and-key fit between the virus and
the receptor (proteins) on the surface of a host cell.
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
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(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
By spreading from one species to a new host
species
By spreading from an isolated location to more
widespread locations
Through the detection of previously
unrecognized viruses
HSV1 vs HSV2
Human Papilloma Virus – 14yo boy
HPV virus – genital warts
Polio Virus
Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating
VIRUS MINI QUIZ
1.
THE PRIMARY FUNCTION OF
ALL VIRUSES IS TO REPLICATE!!
MINI QUIZ…
2. WHAT IS THE
TYPICAL/COMMON VIRUS THAT
STUDENTS STUDY WHEN
LEARNING ABOUT VIRUSES?
T4 Bacteriophage
MINI QUIZ…
3. IN ORDER FOR A VIRUS TO
REPLICATE IT NEEDS TO BE IN A
HOST CELL
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…
6. ANOTHER NAME FOR
INFLUENZA IS FLU VIRUS
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.
3 WAYS THAT VIRUSES CAN BE
TRANSMITTED ARE….
-- droplets in the air (e.g. cold, flu, tuberculosis)
-- via food or water (e.g. Salmonella, food poisoning)
-- via mosquitoes, ticks (e.g. malaria, West Nile virus, Lyme
disease)
-- physical contact (e.g. pinkeye, herpes, chickenpox, sexually
transmitted diseases)
MINI QUIZ…
10. A VIRUS THAT HAS ONLY A CAPSID
SURROUNDING IT’S GENETIC
INFORMATION AND NO ENVELOPE IS
CALLED A NAKED VIRUS.