Viruses are the smallest of all pathogens, ranging from 20-500 nanometers in size, consist of either DNA or RNA surrounded by a protein coat or capsule, and have characteristics of both living and non-living entities. They contain genetic material and can reproduce but only within a host cell by taking over the cell's machinery. Viruses cause infectious disease, come in different shapes, and have the ability to mutate or become dormant.

1. CHARACTERISTICS OF
VIRUSES

2. VIRUSFrom the Latin word meaning "poison“
Pathogen: infectious agent causing disease
Ebola Virus

3. VIRUS STRUCTURE
Viruses are tiny!
Virus: 20 - 500 nm
Bacteria: 200 - 2000 nm
Human Cells: 5000 – 100000
nm

4. VIRUS STRUCTURE
Viruses are acellular
 Not a cell as it has no nucleus, cytoplasm
or organelles
Viruses consist of two main parts:
1. Nucleic Acid – DNA or RNA found at the
core of the virus
2. Capsid – Protein coat surrounding the
genetic material
Some viruses have an outer envelope made
of lipids (fats) and proteins covering the
capsid

5. VIRUS SHAPE
Viruses come in a variety of shapes:
Rod Spherical Irregular or Tadpole

6. LIVING CHARACTERISTICS OF
VIRUSES
Contains genetic material
Able to reproduce (within host cell only)
Able to invade host cell and reprogram cellular machinery
Causes an infectious disease
Able to mutate

7. NON-LIVING CHARACTERISTICS OF
VIRUSES
No metabolic needs – Doesn’t eat, breathe, sleep, produce
etc.
Not made of cells
Able to crystalize and remain dormant
Because viruses contain both living and non-living
characteristics they are considered to be transitional
between life and non-life