1. 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 nm
viroids nm
viruses nm
prokaryotics cells ,000 nm
prion 2-10 nm

2. A prion is made only of proteins.
causes misfolding of other proteins
results in diseases of the brain
A viroid is made only of single-stranded RNA.
causes disease in plants
passed through seeds or pollen

3. Viruses differ in shape, genetic material, and in ways of entering host cells.
non-living pathogen
can infect many organisms
Viruses have a simple structure.
genetic material (either DNA or RNA)
capsid, a protein shell
maybe a lipid envelope, a protective outer coat

4. Viral Shapes: depends on proteins of capsid
enveloped (influenza)
helical (rabies)
polyhedral (foot-and-mouth
disease)
capsid
nucleic acid
lipid envelope
surface proteins
capsid
surface proteins
nucleic acid
capsid
nucleic acid
lipid envelope
Surface proteins

5. A bacteriophage is a virus that infects a bacterium.
capsid
DNA
tail sheath
tail fiber
HEAD
collar
TAIL
Base plate

6. Viruses enter cells in various ways.
bacteriophages pierce host cells
viruses of eukaryotes enter by
endocytosis or fuse with the membrane

7. LYTIC CYCLE