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What are Viruses?: A close look at the smallest of microorganisms

© Neal Rolfe Chamberlain

Viruses are very small forms of life. In fact people still argue over whether viruses are really alive. How small are viruses? Viruses range in size from about 20 to 300 nanometers (nm). How big is a nanometer? A nanometer is 0.000001 of a millimeter. A millimeter is 1/25 of an inch. So in other words you can place 25,000,000 nanometers in an inch. If the biggest virus is 300 nm then you could fit 83,333 of that virus in an inch. Pretty small eh? Other examples of how small viruses are can be found at Virus Ultrastructure site and at Cells alive.

Viruses are major freeloaders. They can not make anything on their own. To reproduce they must infect other living cells. Viruses infect bacteria, parasites, fungi, plants, animals, and humans. No one escapes them. If you have had the flu, chickenpox, measles, a common cold, mono, a cold sore, or a sore throat you have been INFECTED by a virus!!

The simplest viruses have one type of nucleic acid (RNA or DNA) and a protective protein coat. The RNA or DNA helps the virus take over the the cell it infects. The RNA or DNA contains the information that eventually tells the cell to make more viruses.

The protein coat protects the RNA or DNA from being destroyed and helps the virus to attach to the cells it infects. Once the virus infects a cell it will take over the cell and cause the cell to produce many more virus particles (virions). A good place to look at some nice simple cartoons of viruses are found in Baron's online Medical Microbiology textbook. A really good introduction to what viruses are can also be found in this online text.

Viruses come in different basic shapes. A helical symmetry (Tobacco Mosaic Virus), icosohedral symmetry (Human Adenovirus), and complex symmetry (Bacteriophage T4).

Are you interested in viruses and want more information about them? The most fantastic site I have found thus far is The Garry Laboratory Homepage. This site contains information for experienced virologists and for people wanting to know about viruses. Truly, a must see site. Especially, their extensive links page. Another good site for information on viruses is called the Universal Virus Database. They have a large number of the viruses classified and have short descriptions and pictures of the viruses. Another great virus site in addition to the ones above is Dr. Bock's site. This site includes 3D pictures and movies of viruses. There are many more sites I am sure I have missed however, this is a great place to start!

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