Download 18.1 Studying Viruses and Prokaryotes

18.1 Studying Viruses and Prokaryotes
KEY CONCEPT
Infections can be caused in several ways.
Pathogen: Any
living organism or
nonliving particle
that causes an
infectious disease.
18.1 Studying Viruses and Prokaryotes
Viruses, bacteria, viroids, and prions can all cause
infection.
• Any disease-causing agent is called a pathogen.
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
18.1 Studying Viruses and Prokaryotes
• Virus: an infectious particle made only of a strand of
DNA or RNA surrounded by a protein coat. .
– non-living pathogen
– can infect many
organisms
– 50 – 200 nm
• Viroid: Infectious particle
that is made only of
single-stranded RNA.
– causes disease in
plants
– passed through
seeds or pollen
18.1 Studying Viruses and Prokaryotes
• Prion: infectious particle is made only of proteins.
– causes misfolding of other proteins
– results in diseases of the brain
18.1 Studying Viruses and Prokaryotes
How is a virus similar/different from a living organism?
• Similar:
– Contain proteins and DNA
– They can respond to their environment
– Reproduce – but not on their own!
• Different:
– They must infect the host in order to reproduce new
viruses.
– Viruses do not have cellular structure or any
membrane bound organelles.
18.1 Studying Viruses and Prokaryotes