A virus is a single-stranded viral particle, which consists of either an RNA or DNA sequence enclosed in a membrane protein shell. A virus attacks a living host cell and removes its protein coating by damaging the cell’s outer membrane. The virus then uses the cellular resources such as energy and transport to replicate itself thousands of times thus replicating the viral genome. Although each virus produces a unique copy of itself, they are also classified into three main groups; retroviruses, envelopes and bacteria.


Retroviruses are mobile genetic elements that often invade cells and insert themselves into the host cell where they commence replication. The retrovirus can be single stranded or multiple stranded. Single-stranded viruses are quite common, whereas multiple stranded viruses are associated with the bacterium. envelope viruses are quite rare.

Envelopes are viruses that enter host cells, usually in the shape of a prophage cell. These envelopes are made up of DNA with a genetic envelope. They are extremely similar to bacteria (bacteria envelopes) and appear to be quite harmless. They only infect host types and reproduce by budding. They do not reproduce when the host range dies.

Nucleic acids are pieces of DNA code which either encodes a nucleic acid or makes up a nucleic acid base. The DNA bases of viruses and bacteriophages are complementary to one another and can combine to form a polypeptide chain. Polypeptides then function as enzymes which break down proteins either directly or by generating energy to support growth and development. Enzymes also serve to make viral diseases contagious.

Tobacco plant virus, or tobacco mosaic virus for short, is a family of viruses that affect tobacco leaves (inoculation). Tobacco mosaic virus is considered to be the most virulent of all viruses. It causes a great deal of damage to the infected organisms which include death of both the organisms and their essential DNA (genetic material). This virus is capable of replicating itself and thus has the potential to cause great economical and agricultural losses in developing countries. There is a high mortality rate when the infected person becomes a carrier.

Recombinant viruses are produced from a genetic material of a virus that has been genetically modified so as to produce its own altered genetic material; such as the engineered virus created to cure a deadly disease. It is an instance of gene manipulation. These viruses are used to develop vaccines and can be employed to create potent biologics that can attack other viruses and thereby reducing the risks of disease spreading through contact.