Viruses are microscopic particles that can only reproduce inside living host cells. There are several theories about the origin of viruses, including that they evolved from cells, evolved alongside cells, or came to Earth via meteorites. Viruses are simple structures composed of a protein capsid that protects their genetic material, which can be DNA or RNA. Many serious human diseases are caused by viruses, though vaccines can help prevent viral infections by training the immune system to recognize them.

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2. Virus – structure & function
 Viruses are microscopic particles which
 Do not grow / mature Are parasitic, only
reproducing within a living organism

4. Where do Viruses Come From?
 They’ve been around for at least
4000 yeas.
 Small Pox First virus in recorded
history Pharoah Ramses V (1196
B.C.) had the pot marks associated
with small pox.

5. (1) Evolved from Cells
 Some cells evolved into viruses:
 By losing their genetic materials, thus requiring the
genetic material of host cells
 When fragments of a cell’s DNA combined to make
something new (a virus)
(2) Evolved with Cells
 Simple molecules on earth evolved into:
 Cells which have self-replicating abilities
or
 Viruses which have parasitic abilities, using cells to reproduce.
Three Theories on Viruses

6. Three Theories on Viruses
 Idea that viruses came to Earth via a meteor Why such
a strange idea?
 Viruses are so different from everything else on
Earth.
(3) Alien Theory

7. • Viruses are simple structures consisting of
1. Capsid
• A protein coat made of individual protein subunits
called capsomeres.
• Provides the virus with its shape
• Makes up 95% of a virus’s size
Virus – structure & function
2. Genetic Material
• Genetic material is located inside the capsid.
• Can be DNA or RNA

8. Virus – structure & function

9. 1. Spikes
• Located on capsid
• Helps viruses attach to cells
• Not present on all viruses
2. Envelope
• Above capsid
• A protective coat on some
viruses
Virus – structure & function

10. Viruses & Human Health
 Many serious diseases are caused
by viruses
 Symptoms are caused by
destruction of the cell the viruses
infect
 Antibiotics are not effective against
viruses
 Viral diseases can be prevented with vaccines
 The body reacts to the vaccine as though it were the real
disease and produces antibodies

11. How are viruses transmitted?
 Breathing in air-borne
droplets contaminated
with a virus.
 Eating food or drinking
water contaminated with
a virus.
 Having sexual contact
with a person who is
infected with a sexually
transmitted virus.
 Indirect transmission from person to person by a virus
host, such as a mosquito, tick, or field mouse.
 Touching surfaces or body fluids contaminated with a virus.

12. Diseases caused by viruses
 Smallpox
 This variola virus had many forms and
continues to be a required vaccination.
 Smallpox in its worse forms
– hemorrhagic
–flat – had the highest fatality rates with
only a 10 percent or less chance of survival.
 Cancer
 Viral cancers only occur in a minority of
infected persons (or animals).
 Cancer viruses come from a range of virus
families, including both RNA and DNA
viruses.

13. Diseases caused by viruses
 AIDS has been categorized as an epidemic
by the CDC and the life expectancy has
been extended despite the lack of a
vaccination or cure.
 The Ebola virus is much more deadly in the
short term.
 Polio or infantile paralysis is a viral
disease that is transmitted through the
fecal-oral course
 HIV / AIDS
 Human immunodeficiency virus (HIV) leads to acquired immune
deficiency syndrome (AIDS), which cripples a human’s immune
system.

14. Vaccines
 This is a prepared virus that has been HEATED to
kill/destroy the genetic material while leaving the capsid
(protein coat) intact.
 Vaccine is injected into a host, to trigger the immune
system.
 Immune system builds antibodies specific to that virus.

15. The End
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