Virus depends on host that they infected to reproduce. Without a host, viruses exist as a protein coat or capsid and sometime, it is enclosed within a membrane. The protein coat encloses genes that are either DNA or RNA which carry genetic information. When virus comes into contact with a host cell, it can insert its genetic material into its host.
Virus classification
· The nature of viruses do not immediately land themselves to the classical taxonomy
· Viruses only exhibit biological activities inside their hosts.
Lwoff’s scheme for classification
-classification based on shared properties instead of properties of their hosts
-based on nucleic acid of the virus
-symmetry of capsid
-presence or absence of envelop
-the dimensions of virion and capsid.
Baltimore’s system for classification (unlike Lwoff’s, it is not based on physical properties)
- Based on viral genome only and its relationship to mRNA.
- Central dogma of molecular biology.
- According to Baltimore classification of viruses, it is divided into the following seven classes:
