Overview of Virology

A Peek into VIROLOGY

There are 3 main domains of life:

• Eukarya
• Eubacteria
• Archaea

However, viruses do not fall in any of the domains as they are not considered organisms however, they have life-like properties. They depend on other organisms for reproduction and metabolism.

Their common physical characteristics/properties are as follows.

1. Intercellular parasites
2. one type of nucleic acid (either DNA or RNA) - genome
3. no metabolic activity outside host cells

Each virus particle has the following structures:

1. virion - the intact virus particle
2. capsid - protein coat (which protects the viral genome form inactivation by adverse environmental factors)
3. capsomeres - capsid is composed to these (protein sttuctural units)
4. nucleic acid
5. envelope (many virus particles are surrounded by a lipoprotein envelope that contains viral antigens, partly derived from the outer membrane or in some cases, the nuclear membrane of the host cell)

There are 3 types of symmetry shown by virus particles:

1. cubic - particles are icosahedral protein shells with the nucleic acid contained inside
2. helical - particle contains an elongated nucleocapsid & the capsomeres are arranged round the spiral ofthe nucleic acid
3. complex - particles do not conform to none of the above symmetry mentioned