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Biology

Viruses and cellular defence

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Structure of viruses

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.

Two examples of virus structure. Both have a protein coat on the outside, and nucleic acid inside. The influenza virsu has RNA on the insode and an outer membrane envelope. The bacteriophage has DNA inside it, and from that it has a tail, and fibres coming from the end of the tail.
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