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Transcript
Viruses
Living or Not?
Viruses


Virus – Latin for “poison”
Russian Biologist Dmitri Ivanovski (1892) –
 Tobacco Mosaic Disease
 First
virus to be discovered, 1930
 Virus that affects plants
 No effect on humans
Characteristics of Viruses



Among the
smallest biological particles
(not cells) that are capable of
causing disease in living
organisms.
Virus particles are called
VIRIONS
5000 influenza viruses can fit
inside the head of a pin!
Size of a Virus!~

Here is how you can imagine the size of viruses:

If a virus was the size of a basketball:
A
bacterium would be as large as a city block
A
grain of sand would be two miles long
A
person would be 4,000 miles tall
Studying the “T4-Bacteriophage

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




A virus IS NOT a
bacteria, fungus, protist,
plant or animal.
They CAN 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 & CELLS
Characteristic
VIRUS
(non-living)
CELL
(living)
Structure
DNA or RNA core, capsid
Cell membrane, cytoplasm,
nucleus, other organelles
Reproduction
Only within a host
Asexual and sexual
reproduction
Genetic Code
DNA or RNA
DNA
Growth/Dvpmt
NO
Yes
Energy
NO
Yes
Response to Environment No
Yes
Change over time
Yes
Yes
History of Viruses


Invasions, wars, and immigrations 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

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
http://www.mcgrawhill.ca/school/schoolGraphi
cs/biology2_1.mpg
Lytic
(kills cells dead)





Adsorption – attracting and holding other
materials or particles on its surface
Entry – penetration of the cell
Replication – uncoating and replicating
Assembly – maturation / prepare to leave
Release – leaving the cell
How are Viruses Studied?


“Virology” is the study of viruses; scientists
who study viruses are called Virologists.
They use:




electron microscopes to visualize viruses;
cell cultures to grow viruses (although some viruses will only
grow in animals)
techniques from molecular biology, genetics, and
immunology;
proper safety precautions when studying dangerous viruses.
What are Viruses Made of?





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 (bilayer) 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?


Genetic Material
 DNA or
 RNA
 But not both
Capsid Structure




Helical (rod shaped)
Polyhedral
Complex
Helical Marburg
virus
Polyhedral SV40 virus
Presence or absence of a
membranous envelope
surrounding the capsid
Complex bacteriophage
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.
 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:
 Array of host cells that a particular virus can infect

The virus needs a partner

Determined by a lock-and-key fit between the virus and the
receptor on the surface of a host cell.

Flu attack: How Viruses Invade Your Body
http://www.youtube.com/watch?v=Rpj0emEGShQ

What Diseases are Caused by
Viruses?


Infectious diseases
RNA viruses (retroviruses)
DNA viruses
(mutates more often)
(more stable)
AIDS
Respiratory Disease
Influenza (flu)
Smallpox
Common cold
Chickenpox
Polio
Mononucleosis
Measles
Cold Sores
Cancer
How Can Viral Diseases Be
Prevented and Treated?

Good hygiene



Vaccines





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)


Available for only a few viruses.
Inhibit some virus development and/or relieve symptoms.
How Do New Viruses Emerge?




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
How do Our Bodies Fight Viruses?
Function of the Immune System
 Recognition:


Destruction:




Antibodies (proteins that bind to the surface of a virus)
recognize an infected cell and attach
White cells move in to destroy the infected cells
Also known as leucocytes 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
HSV1 * vs HSV2
Human Papilloma Virus – 14yo boy
(think Tree Man)
http://www.youtube.com/watch?v=DStwXsmZ3OE
http://www.youtube.com/watch?v=K8v3VzEyp88
Polio Virus
Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating
Polio – primarily affects children!
Epstein Barr Virus (EBV) – Kissing
Disease

From the Herpes Family




Causes mono
95% of all adults have
been infected with EBV
Requires intimate contact
with the saliva of an
infected person – not
common in air/blood
Linked to rare forms of
cancer

Salmon
http://www.abs-cbnnews.com/global-filipino/world/10/17/11/lethal-european-fishvirus-found-canada
VIRUS MINI QUIZ
1.
THE PRIMARY FUNCTION OF
ALL VIRUSES IS TO
___________________
MINI QUIZ…
2. WHAT IS THE
TYPICAL/COMMON VIRUS THAT
STUDENTS STUDY WHEN
LEARNING ABOUT VIRUSES?
MINI QUIZ…
3. IN ORDER FOR A VIRUS TO
REPLICATE IT NEEDS TO BE IN A
__________ CELL
MINI QUIZ…
4. VIRAL REPRODUCTION THAT
KILLS THE HOST CELL IS
CALLED THE ___________ CYCLE!
MINI QUIZ…
5. WHEN VIRAL DNA IS EMBEDDED
INTO A HOST CELL’S DNA IT
FORMS A _______________
MINI QUIZ…
6. ANOTHER NAME FOR
INFLUENZA IS __________
MINI QUIZ…
7. 3 WAYS VIRUSES CAN BE
TREATED/PREVENTED ARE….
MINI QUIZ…
8. SCIENTISTS THAT STUDY
VIRUSES ARE CALLED
_________________
MINI QUIZ…
9. 3 WAYS THAT VIRUSES CAN BE
TRANSMITTED ARE….
MINI QUIZ…
10. A VIRUS THAT HAS ONLY A CAPSID
SURROUNDING IT’S GENETIC
INFORMATION AND NO ENVELOPE IS
CALLED A ______________ VIRUS.