Virus

HIV Virus

What are Viruses? 

A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.

 

Are Viruses Living or Non-living?

Viruses are both and neither. They have some properties of life but not others. For example, viruses can be killed, even crystallized like table salt. However, they can’t maintain a constant internal state (homeostasis).

Discovery of Viruses

- Beijerinck (1897) coined the Latin name “virus” meaning poison.

- He studied filtered plant juices & found they caused healthy plants to become sick.

- Wendell Stanley (1935) crystallized sap from sick tobacco plants.

- He discovered viruses were made of nucleic acid and protein.

- Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses.

- Deadly viruses are said to be virulent.

- Smallpox has been eradicated in the world today.

Size of Viruses

Characteristics

- Non living structures.

- Noncellular.

- Contain a protein coat called the capsid.

- Have a nucleic acid core containing DNA or RNA.

- Capable of reproducing only when inside a HOST cell.

- Some viruses are enclosed in an protective envelope.

- Some viruses may have spikes to help attach to the host cell.

- Most viruses infect only SPECIFIC host cells.

- Viral capsids (coats) are made of individual protein subunits.

- Individual subunits are called capsomeres.

- Outside of host cells, viruses are inactive.

- Lack ribosomes and enzymes needed for metabolism.

- Use the raw materials and enzymes of the host cell to be able to reproduce.

- Some viruses cause disease.

- Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola.

- Some viruses may cause some cancers like leukemia

Virus-free cells are rare.

Viral Shapes

- Viruses come in a variety of shapes.

- Some may be helical shape like the Ebola virus.

- Some may be polyhedral shapes like the influenza virus.

- Others have more complex shapes like bacteriophages.

Used for Virus Identification

- RNA or DNA Virus.

- Do or do NOT have an envelope.

- Capsid shape.

- HOST they infect.