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Viruses 20-1

Viruses 20-1. Federoff. Discovery of Viruses. Ivanovski (1892) found the tobacco mosaic disease was found in liquid from infected plants. Beijernick (1897) found small particles in this liquid and named them viruses .

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Viruses 20-1

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  1. Viruses 20-1 Federoff

  2. Discovery of Viruses • Ivanovski (1892) found the tobacco mosaic disease was found in liquid from infected plants. • Beijernick (1897) found small particles in this liquid and named them viruses. • Stanley (1935) isolated crystals of tobacco mosaic virus. Inferred viruses were not truly alive.

  3. Discovery of Viruses • A virus is a nonliving particle made of proteins, nucleic acids, and sometimes lipids.

  4. Structure and Composition • Viruses are very small. Simple viruses contain only a few genes whereas the most complex may have more than a 100 genes. • The protein coat surrounding a virus is called a capsid.

  5. Structure and Composition • Most viruses have proteins on their surface membrane or capsid that bind to receptor proteins on the host cell. • The proteins “trick” the cell to take the virus, or in some cases just its genetic material, into the cell. • Inside the cell, viral genes are copied and may destroy the cell.

  6. Structure and Composition • Most viruses infect only a very specific kind of cell. • Plant viruses infect plant cells; most animal viruses infect only certain related species of animals; viruses that infect bacteria are called bacteriophages.

  7. Viral Infections • Inside living cells, viruses use their genetic information to make multiple copies of themselves. Some viruses replicate immediately, while others initially persist in an inactive state within the host.

  8. Lytic Infections • In a lytic infection, a virus enters a bacterial cell, makes copies of itself and causes the cell to burst, or lyse. • The virus enters the cell and immediately reproduces and hijacks the cell to make copies of the cell till it bursts (lyses).

  9. Lysogenic Infection • An infection where a host cell is not immediately taken over is a lysogenic infection. • Prophage is a bacteriophage’s DNA that becomes imbedded in the host’s DNA.

  10. Lysogenic Infection • The viral DNA becomes embedded in the host and inactive until a trigger (radiation, heat, chemicals, etc.) and it then becomes active.

  11. A closer look at 2 RNA viruses • In humans, RNA viruses cause a wide range of infections, form relatively mild colds to severe cases of HIV. • About 70% of viruses contain RNA rather than DNA.

  12. The Common Cold • Capsid is engulfed inside a cell where viral proteins make new copies of viral RNA and in roughly 8 hours bursts the host cell.

  13. HIV • HIV is a retrovirus. • A retrovirus is one that is copied from RNA to DNA instead of DNA to RNA.

  14. HIV • First it makes a viral DNA copy of its RNA which inserts into the DNA of the host. • It can remain inactive, but once activated it will begin to destroy all body systems used to fight infection

  15. Viruses and Cells • All viruses are parasites. • Viruses are NOT living because they don’t grow and develop, use energy or respond to the environment. • BUT viruses do have structure, reproduce using a host cell, have nucleic acids and change over time.

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