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Capsid

Viruses are composed of nucleic acids enclosed in a protein coat and are smaller than the smallest bacteria. Capsid. Nucleic Acid. What is a Virus?. Section 18.1 Summary – pages 475-483. Most biologists consider viruses to be nonliving because:. They don’t 1. carry out respiration

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Capsid

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  1. Viruses are composed of nucleic acids enclosed in a protein coat and are smaller than the smallest bacteria. Capsid Nucleic Acid

  2. What is a Virus? Section 18.1 Summary – pages 475-483 Most biologists consider viruses to be nonliving because: They don’t 1. carry out respiration • grow • develop * All viruses can do is replicate—make copies of themselves—and they can’t even do that without the help of Host cells.

  3. What is a Host Cell? A cell in which a virus replicates inside of is called the host cell.

  4. What are viruses named after? Section 18.1 Summary – pages 475-483 Viruses, such as rabies viruses and polioviruses, were named after the diseases they cause. • Other viruses were named for the organ or tissue they infect.

  5. Viral Structure Section 18.1 Summary – pages 475-483 • A virus has an inner core of nucleic acid, either RNA or DNA (JUST LIKE A CELL HAS DNA…BOTH HAVE GENETIC MATERIAL) and an outer protein coat called a capsid. Capsid Nucleic acid

  6. Viral Structure Section 18.1 Summary – pages 475-483 Capsid • Some relatively large viruses, such as human flu viruses, may have an additional layer, called an envelope, surrounding their capsids. Nucleic acid Envelope

  7. Section 18.1 Summary – pages 475-483 Before a virus can replicate, it must enter a host cell. A virus attaches to a host cell when one of its proteins interlocks with the receptor site on the host cell’s plasma membrane. Virus

  8. VIRUS SHAPES Polyhedral virus shape Human Papilloma Virus Envelope studded with projections (flu and AIDS)

  9. VIRUS SHAPES Long narrow helical shape (Tobacco Mosaic Virus) Polyhedral-shaped head attached to a cylindrical tail with leg-like fibers

  10. Section 18.1 Summary – pages 475-483 Viral Attachment to Host • Each virus has a specifically shaped attachment protein. Therefore, each virus can usually attach to only a few kinds of cells. • In general, viruses are species specific, and some also are cell-type specific. For example, polio viruses normally infect only intestinal and nerve cells.

  11. Section 18.1 Summary – pages 475-483 • The species specific characteristic of viruses is significant for controlling the spread of viral diseases. For example, smallpox was easier to eradicate because it only affects humans (unlike the flu and West Nile that affect several types of animals.)

  12. Section 18.1 Summary – pages 475-483 Viral Replication • Once attached to the plasma membrane of the host cell, the virus enters the cell and takes over its metabolism. Cells VS Viruses • Virus= non-living • Viruses= need a host cell • Both have DNA or RNA • Cells= Use Energy • Viruses= Cannot Use Energy

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