Viruses and bacteria are microscopic organisms that can cause infection. Viruses are non-living particles that enter and reproduce inside living cells. They come in various shapes and sizes smaller than cells, and have a protein coat and genetic material. Bacteria are single-celled organisms that lack a nucleus and other structures found in more complex cells. They also appear in different shapes and sizes around 0.5-1 micrometer. Both viruses and bacteria can infect and potentially harm their host cells.

1. Viruses and Bacteria

2. Viruses
• A tiny, non-living particle that enters
and then reproduces inside a living cell
• Needs a host, which provides a source
of energy
• Parasite
– Lives on or in a host and can cause
harm

3. Shapes
• Round, rod-shaped, bricks, threads,
bullets, robot-like shapes

5. Sizes
• Smaller than cells
• Cannot be seen with school
microscopes
• Measured in nanometers
– 1 billionth of a meter

6. Structure
• Two basic parts
– Protein coat which protects itself
– Inner core
• Genetic material

7. Surface Proteins
• Can attach to host cells
• Lock and key
• Specific

8. Multiply
• Inside host cell
– Virus’s genetic material takes over many
cell functions
– Instructs cell to produce the virus proteins
and genetic material
– Make new virus’s

9. Bacteria
• Anton van Leeuwenhoek (late 1600s)
– Scrapings from teeth
– Could only see shapes, but not the parts
inside the cells

10. Bacteria
• Prokaryotes
– Genetic material is not contained in a
nucleus (have no nucleus)
– Lack some other structures as well

11. Shapes and Sizes
• Spherical, rodlike, spiral
• Vary in size, average is about 0.5-1
micrometer
– 1 millionth of a meter