Most people think of viruses as dangerous and harmful little organisms. However, they are far from it. In reality, viruses play an integral role in the evolutionary development of life on earth. They reproduce within living cells, and they infect other living cells, usually causing serious damage. A well-designed immune system can easily overcome these types of viruses.


The life cycle of a virus is similar to that of an infectious agent. The infectious agent must invade and infect a host cell first before spreading out into the body. The infected cell will display symptoms similar to those of a common cold or flu. An example of such a virus is HIV.

Once a virus has infected a host cell, it stays in the host’s cytoplasm, (the fluid that fills all the cellular organs). It waits for something to trigger its entrance into the body, such as exposing it to a toxin or bacteria. When the virus eventually triggers an attack on the body, it produces a protein called a prion. The virion contains genetic instructions that help it replicate itself.

Viruses can be single stranded or double stranded, and they can be in a linear or circular form. The double-stranded form of a virus is best studied by geneticists. They reveal the basic mechanism of replication: when the virus replicates, it cuts a piece of its DNA in half, and then it uses both the halves for another generation of virus. There is also a type of viral disease that causes the body’s immune system to fight itself instead of the invading virus.

It is important to note that the structure of the virus is extremely small, about the size of a virus molecule. Therefore, these viruses do not have outer protective shells that protect their hosts from infection. These viruses are much smaller than bacteria, or even the bacteria that form bacteria. A virus that makes bacteria is much larger than a virus that makes only cells.

When a virus enters a host cell, it triggers an alarm, or pore, on the cell surface receptors. This is a protein receptor that recognizes only the virus. If the virus invades this pore, or if the cell surface receptor is disrupted by the virus, this disruption causes the virus to be trapped inside the pore, or a defect in the cell membrane results. If the defective cell membrane is on the entire virus, the virus is unable to replicate.