Viruses and cellular defence
Viruses are often considered non-living as they exist in an inert state outside of a host cell [cell: Basic unit of life. Unicellular organisms only have one cell. Multicellular organisms have many cells.] . They consist of a strand of nucleic acid, either DNA [DNA: The material inside the nucleus of cells, carrying genetic information. DNA stands for Deoxyribonucleic Acid.] or RNA [RNA: (Ribonucleic acid) - it converts the genetic information stored in DNA into proteins] , surrounded by a protective protein coat (the capsid). Sometimes they have a further membrane of lipid, referred to as an envelope, surrounding the protein. They may also have a tail section.
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