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Download 18.2 Viral Structure and Reproduction
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18.2 Viral Structure and Reproduction Viruses, bacteria, viroids, and prions can all cause infection. • Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells 10,000-100,000 nm viruses 50-200 nm prokaryotics cells 200-10,000 nm viroids 5-150 nm prion 2-10 nm 18.2 Viral Structure and Reproduction • A prion is made only of proteins. – causes misfolding of other proteins – results in diseases of the brain • A viroid is made only of single-stranded RNA. – causes disease in plants – passed through seeds or pollen 18.2 Viral Structure and Reproduction Viruses differ in shape, genetic material, and in ways of entering host cells. – non-living pathogen – can infect many organisms • Viruses have a simple structure. – genetic material (either DNA or RNA) – capsid, a protein shell – maybe a lipid envelope, a protective outer coat 18.2 Viral Structure and Reproduction Viral Shapes: depends on proteins of capsid enveloped (influenza) capsid nucleic acid lipid envelope helical (rabies) Surface proteins capsid nucleic acid surface proteins lipid envelope polyhedral (foot-and-mouth disease) surface proteins capsid nucleic acid 18.2 Viral Structure and Reproduction • A bacteriophage is a virus that infects a bacterium. capsid HEAD DNA collar tail sheath TAIL Base plate tail fiber 18.2 Viral Structure and Reproduction • Viruses enter cells in various ways. – bacteriophages pierce host cells – viruses of eukaryotes enter by endocytosis or fuse with the membrane 18.2 Viral Structure and Reproduction LYTIC CYCLE 18.2 Viral Structure and Reproduction
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