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What are viruses

Virus is an infective agent that tyically consists of a nucleic acid molecule in a

Protein coat. Viruses are the smallest living organisms. Ranging in size from about
20- 300nm.

- Characteristics -
They do not have a cellular structure
They can only reproduce by invading living cells
They are all parasitic
Each type of virus will recognise and infect only certain types of cell
They are on the boundary between what we regard as living and
Non- living
Nucleic acid can be either DNA or RNA
Molecules on virus surface impart high specificity for attachment to host
cell

Structure of the viruses

Basic nucleocapsid structures

H.P.G.P Wimalasiri (TG/2018/436)