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. Classifying Viruses• Can be grouped
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. Cylinders: The tobacco mosaic virus
Is shaped like a cylinder and attacks
tobacco plants.
Crystals: The polio virus is shaped like
the crystal shown here.
8. Spacecraft: One group of viruses attacks
only bacteria. Many of these look almost
like spacecraft (also called
Bacteriophage).
Spheres: Influenza viruses look like
spheres. HIV is another virus that has
this structure.
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
VirusVirus AffectsAffects
What?What?
Which organisms?Which organisms?
Tobacco mosaicTobacco mosaic PlantsPlants Tobacco, tomato,Tobacco, tomato,
pepperspeppers
Potato XPotato X PlantsPlants Potatoes, tomatoes,Potatoes, tomatoes,
pepperspeppers
AdenovirusAdenovirus AnimalsAnimals Humans & otherHumans & other
vertebratesvertebrates
HIVHIV AnimalsAnimals Humans & otherHumans & other
primatesprimates
BacteriophageBacteriophage BacteriaBacteria E.Coli & otherE.Coli & other
bacteriabacteria
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
