2. It’s a Small World
• Virus: a microscopic particle that gets inside
a cell and often destroys the cell
• Viruses are tiny
• Smaller than the smallest bacteria
• Change rapidly
• So small and change so often that
scientists don’t know exactly how many
types exist
• These properties make viruses difficult to
fight
3.
4. Are Viruses Living?
• Like living things, viruses contain
protein and genetic material
• But viruses don’t act like living things
• Can’t eat, grow, or break down food
• Can’t use oxygen
• Cannot function on its own
5. • Can only reproduce
inside a living cell
that serves as a host
• Host: an organism
from which a parasite
takes food or shelter
• Virus uses host’s cell
as a tiny factory, and
forces host to make
viruses rather than
healthy new cells
6. • Can be grouped Classifying Viruses
together by:
• Their shape
• Type of disease
they cause
• Life cycle
• Kind of genetic
material they
contain
• There are 4 main
shapes of viruses:
7. Crystals: The polio virus is shaped like
the crystal shown here.
Cylinders: The tobacco mosaic virus
Is shaped like a cylinder and attacks
tobacco plants.
8. Spheres: Influenza viruses look like
spheres. HIV is another virus that has
this structure.
Spacecraft: One group of viruses attacks
only bacteria. Many of these look almost
like spacecraft (also called
Bacteriophage).
9. • Every virus is made up of genetic material
inside a protein coat (also known as capsid)
• The protein coat protects the genetic material
and helps a virus enter a host cell
• Many viruses have protein coat that matches
characteristics of their specific host
• There are 4 main shapes of viruses: crystals,
spheres, cylinders, and spacecraft
Capsid: protein coat that
surrounds virus
10.
11.
12. Genetic Material
• Genetic material either DNA or RNA
• Most RNA is made up of one strand of nucleotides,
most DNA is two strands of nucleotides
• Both DNA and RNA contain info for making
proteins
• Example: viruses that cause chickenpox & warts
contain DNA
• Example: viruses that cause flu, HIV, and common
cold contain RNA
13. • One strain of virus cannot infect both plants and
animals
Virus Affects Which organisms?
What?
Tobacco mosaic Plants Tobacco, tomato,
peppers
Potato X Plants Potatoes, tomatoes,
peppers
Adenovirus Animals Humans & other
vertebrates
HIV Animals Humans & other
primates
Bacteriophage Bacteria E.Coli & other
bacteria
16. A Destructive House Guest
• One thing that viruses
do that living things also
do is make more of
themselves
• Viruses attack living
cells and turn them into
virus factories
• The cycle if a virus
incorporating its genes
into the genes of a host
cell is called : THE
LYTIC CYCLE
17.
18. A Time Bomb
• Some viruses don’t go straight into lytic
cycle—they put genetic material in host
cells, but don’t make new viruses right
away
• In the lysogenic cycle, each new cells gets
a copy of the virus’s genes when the host
cell divides
• The genes stay inactive for a long time
• When they do become active, they begin
the lytic cycle and make copies of the virus
19.
20. Treating a Virus
• Antibiotics don’t kill
viruses
• Scientists have
developed antiviral
medications
• Because many viral
diseases do not have a
cure, it is best to
prevent a viral infection
from happening in the
first place
21. • Childhood
vaccinations give
your immune
system a “head
start” on fighting
viruses
• Vaccinations need
to be kept current
• Also a good
practice to always
wash your hands
