Viruses are microscopic which can be seen only under electron microscope. They do not display, any characteristic of life out side of a living cell.

Virology is the study of viruses: their structure and classification, how they infect and exploit cells to replicate and cause disease, the techniques to isolate and culture them, and their potential uses in research and therapy.

General Characteristics of Viruses

Viruses

• are acellular or have no any cellular structures.
• contain a single type of Nucleic acid, either DNA or RNA.
• enclosed within a Protein coat Capsid.
• have few or no enzymes of their own for metabolism.
• are metabolically inert or no respiration, excretion, homeostasis, DNA and Protein synthesis.
• are obligate intracellular parasites or require host cell to reproduce.
• are specific to their hosts.
• can be crystalized.
• cannot be cultured in a nutrient medium.
• can mutate or evolve.

Composition of Viral Structure

Viruses display a wide diversity of shapes and sizes, called morphologies. Generally viruses are much smaller than bacteria. Most viruses that have been studied have a diameter between 10 and 300 nanometers. Some filoviruses have a total length of up to 1400 nm; their diameters are only about 80 nm.