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Adenovirus - cause of the common cold
Viruses
Viruses are insidious pathogens, they attack cells from the
inside. They hijack your own DNA and use it against
you. A virus cannot be treated with antibiotics, it can only
run its course until your immune system kicks it out.
..Even then, the virus may lay dormant within the cells and
come back at a later date
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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!
Properties of a Virus:
no membranes, cytoplasm, ribosomes, or other cellular
components
they cannot move or grow
they can only reproduce inside a host cell
they consist of 2 major parts - a protein coat, and hereditary
material (DNA or RNA)
they are extremely tiny, much smaller than a cell and only
visible with advanced electron microscopes
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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!
How Are Viruses Named?
1. Nature of the nucleic acid (DNA or RNA)
2. Protein shell and symmetry
3. Geographic Origin
4. Year of Isolation
5. Named after the infected species (Swine Flu, Avian Flu..)
6. Named after a person (either a patient or a doctor)
Example of an Influenza Virus
How are Viruses Classified?
1. Genetic Material
 DNA or
 RNA (retrovirus/mutates
frequently)
 But not both
2. Capsid (Protein) Structure (95%
of virus)
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Helical (rod shaped)
Polyhedral (spherical)
Complex
Helical Marburg
virus
Polyhedral SV40 virus
3. Presence or absence of a
membranous envelope surrounding
the capsid
**No envelope = naked virus
Complex bacteriophage
Virus Structure
Parasitic Nature
Obligate intracellular parasites (they cannot exist independently)
Specific to hosts (human, dog, some can cross species)
Specific to cells , the common cold is a virus that specifically
attacks cells of the respiratory track (hence the coughing and
sneezing and sniffling). HIV specifically attacks white blood
cells
This is a bacteriophage, a type of virus that
attacks bacteria. It is recognizeable
because it looks like the lunar landing
spaceship.
**Most widely studied virus!!!
See
animation http://www.youtube.com/watch?v=41aqxcxsX2w&feature=
related
Viral Reproduction
Lytic cycle = ACTIVE…reproduction occurs, cells burst
Lysogenic cycle = DORMANT…reproduction does not
immediately occur
Virulent = viruses that undergo both cycles
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 protein
Ex: 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.
Emerging Viruses:
illnesses not previously known
AIDS, West Nile Virus, SARS, Ebola, Bird Flu
http://www.youtube.com/watch?v=rI11hHOya34
• Could be genetic code mutations of known viruses…protein
coat changes that are unrecognizable to host’s immune system
• Could be viruses exposed when new areas were developed
(DISRUPTION)
• Could have jumped species (avian flu, swine flu)
• Connectivity (air travel)
Zoanosis
Reservoir Host
Spillover
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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How Can Viral Diseases Be
Prevented and Treated?
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.
There are two FDA-approved antiviral drugs recommended by CDC. The brand
names for these are Tamiflu® (generic name oseltamivir) and Relenza® (generic
name zanamivir).
Used to relieve symptoms
Other antivirals block the viruses at various stages of their life cycle, such as
blocking cell receptors, preventing attachment or preventing viral repication after
the virus has entered the cell.
Some parents are
opting out of
immunizations due to
fears about vaccine
safety.
In response,
government agencies
are producing
commercials to
encourage parents to
get their child
vaccinated.
Discuss:
1. What are the risks of vaccines? Are they safe?
2. Would you have your own child vaccinated?
3. Should the government force immunizations?
RV = rotovirus; DTaP = diptheria, tetanus, pertussis (whooping cough); Hib =
haemophilus influenza type B; PCV = pneumococcal vaccine; IPV =
inactivated polio virus; MMR = measles, mumps, rubella,
Retroviruses -- RNA viruses that have a DNA stage
• Human Immunodefiency Virus - causes AIDS
• Retrovirus (RNA inside a protein coat)
• Reverse Transcriptase makes DNA from the virus RNA
• DNA inserts into host DNA
• Proteins are assembled from the DNA code
• Viruses assembled from the proteins
• Viruses released from the cell
(Link) HIV Animation - how virus infects cells
What we know about HIV.....
Developing a vaccine for AIDS is difficult because it is a
RETROVIRUS. RNA mutates easily and each individual virus can be
slightly different from the others. In fact, different viruses can exist
within the same person.
HSV1 vs HSV2
Human Papilloma Virus – 14yo boy
http://www.youtube.com/watch?v=mJxAC5
E40
Polio Virus
Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating
Now Let’s Check Your
Knowledge!!
Mini Virus Quiz
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.