Compléter VirusVersion en ligne First part par David Gonzalez 1 lipids small RNA envelope microscopic single smallest living acid host fatty DNA collection Virus , an infectious agent of size and simple composition which can multiply only in cells of animals , plants or bacteria . Viruses are ; they range in size from about 20 t0 250 nanometers in diameter . By contrast the bacteria are about 400 nanometers in size . A virus consists of a - or double stranded nucleic core surrounded by a protein capsid ; some viruses also have an outer composed of materials ( ) and proteins . The nucleic acid core carries the virus's genome ? its of genes ? and may consist of either deoxyribonucleic acid ( ) or ribonucleic acid ( ) . The protein capsid provides protection for the nucleic acid and may contain molecules that enable the virus to enter its appropriate cell .
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