Chapter 6

Chapter 6 - Chapter6 Generalcharacteristicsofviruses...

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Chapter 6  •General characteristics of viruses -Are they living organisms? -Obligate intracellular parasites -Contain either RNA or DNA -Use the metabolic machinery of host cell to synthesize their own nucleic  acids -They have no or just few enzymes of their own  -Can infect: animals, plants, algae, fungi, and bacteria The size of viruses ranges from 20 to 14,000 nm •Viral Components -Naked viruses *Viral particles is composed of  ~Nucleic acid ~Protein coat–capsid •Capsid is composed of protein subunits called  capsomeres -Envelope viruses •Some viruses have the capsid covered with an envelope (lipids,  proteins, and carbohydrates) •Morphology Viruses -Based on capsid structure there are 3 different morphological types of  viruses: -Helical -Polyhedral -Complex •Helical -Naked *Long rods *The capsid is cylindrical with helical structure (i.e. tobacco mosaic  virus)
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-Envelope •Helical nucleocapsid placed within an envelope (i.e. influenza) •Polyhedral -The capsid is a regular polyhedron (icosahedrons) with 20 triangular  faces (poliovirus) -Nucleic acid packed in center •Viral Envelope -Roughly spherical -Sometimes the envelope is covered with spikes (carbohydrates) -Function of capsid/envelope: •Protection •Attachment of viruses to host cells •Introduction of nucleic acid into the host cell •Complex viruses -Bacterial viruses––bacteriophages -Head  polyhedral -Tail -Tail fibers •At the core of a virus
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Chapter 6 - Chapter6 Generalcharacteristicsofviruses...

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