What is a Virus?
Virus is a non-cellular, microscopic infectious agents that can only replicate inside a host cell. From a biological perspective, viruses cannot be classified as either a living organism or non-living. This is due to the fact that they possess certain defining characteristic features of living organisms and non-living entities. The study of viruses is known as virology, a sub-specialty of microbiology.
Infectious entity made up of genetic material and protein that can invade and reproduce only within the living cells of bacteria, plants, and animals. For instance, a virus cannot replicate itself outside the host cell. This is because viruses lack the required cellular machinery. Therefore, it enters and attaches itself to a specific host cell, injects its genetic material, reproduces by using the host genetic material, and finally, the host cell splits open, releasing the new viruses.
Viruses can also be crystallized, which no other living organisms can do. It is these factors that lead to viruses being classified in the grey area – between the living and non-living.
Structure and Function of Viruses
Viruses are tiny and smaller in its size, ranging between 30-50 nm. They usually lack a cell wall but are surrounded by a protective protein coating called the capsid. It can be seen as a genetic element and is characterized by the combined evolution of the virus and the host. They contain either RNA or DNA as the genetic material
A complete virus particle, known as a virion, consists of nucleic acid surrounded by a protective coat of protein called a capsid. These are formed from identical protein subunits called capsomeres. Viruses can have a lipid “envelope” derived from the host cell membrane.
The capsid is made from proteins encoded by the viral genome and its shape serves as the basis for morphological distinction. Virally-coded protein subunits will self-assemble to form a capsid, in general requiring the presence of the virus genome. Complex viruses code for proteins that assist in the construction of their capsid. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid. The capsid and entire virus structure can be mechanically (physically) probed through atomic force microscopy. In general, there are four main morphological.
List of Viral Diseases