| What Is a Virus? A virus is an extremely
tiny infectious agent that is only able to live inside a cell.
Basically, viruses are composed of just two parts. The outer part is a protective shell
made of protein. This shell is often surrounded by another protective layer or envelope,
made of protein or lipids (fats). The inner part is made of genetic material, either RNA
or DNA.
A virus does not have any other structures (called organelles) that living cells have,
like a nucleus or mitochondria. These organelles are the tiny organs that maintain a
cell's metabolism (life processes). A virus has no metabolism at all.
Because a virus lacks organelles, it cannot reproduce by itself. To reproduce, a virus
invades a cell within the body of a human or other creature, called the host. Each type of
virus has particular types of host creatures and host cells that it will invade
successfully.
Once within the host cell, the virus uses the cell's own organelles to produce more
viruses. In essence, the virus forces the cell to replicate the virus' own genetic
material and protective shell. Once replicated, the new viruses leave the host cell and
are ready to invade others.
The above is only a very brief sketch of the nature of viruses. If you wish to learn
more, basic biology textbooks are good sources of information.
The image below is an electron micrograph of Sin Nombre virus particles. Sin
Nombre virus is one of the hantaviruses associated with HPS
. Thin-section
electron micrograph of Sin Nombre virus isolate, a causative agent of hantavirus pulmonary
syndrome (HPS). From the 1994 outbreak of HPS in the southwestern United States.
Electron micrograph.
High-resolution view
|
National
Center for Infectious Diseases
