Download 18.1 Studying Viruses and Prokaryotes

18.1 Studying Viruses and Prokaryotes
KEY CONCEPT
Infections can be caused in several ways.
Figure: This
bacteria lives in
the lining of an
esophagus, the
tube that leads
from the mouth
to the stomach.
At one time, it
was thought that
nothing could
survive in an
esophagus, but
the entire
digestive tract is
home for many
types of bacteria.
18.1 Studying Viruses and Prokaryotes
Viruses, bacteria, viroids, and prions can all cause
infection.
• Any disease-causing agent is called a pathogen.
Synthesize: Why are viruses, viroids and prions not included in the Linnaean system
of biological classification?
1 nanometer (nm) = one
billionth of a meter
100 nm
eukaryotics cells
10,000-100,000 nm
viruses
50-200 nm
prokaryotics cells
200-10,000 nm
viroids
5-150 nm
prion
2-10 nm
Figure: Although eukaryotic and prokaryotic cells can be microscopic,
they are large in comparison to viruses, viroids, and prions.
18.1 Studying Viruses and Prokaryotes
• A virus is made of DNA or RNA and a protein coat.
– non-living pathogen
– can infect many
organisms
• A viroid is made only
of single-stranded
RNA.
– causes disease in
plants
– passed through
seeds or pollen
Figure: Polyhedral viruses are manysided, like the one shown here that
causes foot-and-mouth disease in
animals. (computer illustration)
18.1 Studying Viruses and Prokaryotes
Viruses differ in shape and in ways of entering host
cells.
• Viruses have a simple structure.
– genetic material
– capsid, a protein shell
– maybe a lipid envelope, a protective outer coat
enveloped
(influenza)
capsid
nucleic acid
lipid
envelope
helical
(rabies)
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
polyhedral
(foot-and-mouth
disease)
surface
proteins
capsid
nucleic acid
18.1 Studying Viruses and Prokaryotes
• Bacteriophages are viruses that infect bacteria.
capsid
DNA
tail sheath
tail fiber
Root words:
-phage – means
“to eat”
So literally
bacteriophage
means bacteria
eater.
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– influenza
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– common cold
– influenza
– SARS
18.1 Studying Viruses and Prokaryotes
Viruses cause many infectious diseases
• There are many examples of viral infections.
– HIV
• The body has
natural
defenses
against viruses.
HIV-infected
white
blood cell
18.1 Studying Viruses and Prokaryotes
Vaccines are made from weakened pathogens.
• A vaccine stimulates the body’s own immune response.
• Vaccines prepare the immune system for a future attack.
• Vaccines are the only way to control the spread of viral
disease.
18.1 Studying Viruses and Prokaryotes
• A prion is made only of proteins.
– causes misfolding of other proteins
– results in diseases of the brain