KEY CONCEPT Infections can be caused in several ways'

1
KEY CONCEPT Infections can be caused in several
ways.
2
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 cells10,000-100,000 nm
viroids5-150 nm
viruses50-200 nm
prokaryotics cells200-10,000 nm
prion2-10 nm
3

• 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

4

• A prion is made only of proteins.

• causes misfolding of other proteins
• results in diseases of the brain