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Viruses

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  1. Viruses

  2. Are viruses living? • No! They are non-living but they depend on the living.

  3. Can you think of any viruses? • H1N1 • West Nile • Seasonal Influenza (the flu) • HIV • Chicken Pox • Rabies • Ebola

  4. Size comparison Viruses and Bacteria Viruses are very small particles and measured in nanometres (1000nm = 1μm) size demonstration

  5. *VIRUS* • Microscopic particles capable of reproducing only within living cells.

  6. *2 main components* Capsid • 1. Capsid • Protein outer coat • Covers the nucleic acid and protects it • 2. Nucleic Acid Core • Genetic material consisting of either DNA or RNA Genetic material

  7. There are specific viruses which infect animal, plant or bacterial cells. • Those that infect bacteria are called bacteriophages.

  8. *Bacteriophages Replicate in 2 ways…* • Virulent phages replicate actively and cause lysis. • Temperate phages lie dormant for varying periods of time, and can pass through generations attached to a chromosome. They cause lysogeneis.

  9. Basic structure of a virus Bacteriophages helical Some form of nucleic acid (DNA or RNA) Enclosed in a protein coat. (capsid)

  10. Viruses are specific to… • organism - ex. Hanta virus - carried in mice (have no effect) but fatal to humans b) cell type - ex. human cold virus only attacks cells lining the respiratory tract. ans

  11. Viruses are able to reproduce ONLY inside living host cells. • They use the cell's genetic machinery (ribosomes, enzymes) to reproduce viral parts. • They are then assembled into many new viruses which may rupture the cell (destroying it), releasing these viruses to infect more cells. • Viruses can be considered to be intracellular parasites.

  12. *Viruses may enter animal cells in 3 possible ways:* • Attachment and Injection • Endocytosis • Membrane fusion

  13. 1) Attachement and Injection • Capsid remains on outside of host cell Eg. Bacteriophage Virus attaches to the bacterial cell and injects its genetic material into the cell through a tiny syringe.

  14. 2) Endocytosis • The cell swallows up the virus through phagocytosis. • After entering the cell, the virus sheds its capsid (decapsidation), and the viral genetic material takes over the cell.

  15. 3) Membrane Fusion • Some viruses have a membrane (from a previous cell) that they fuse to the cell membrane and get inside the cell. • Once inside, decapsidation occurs and the virus takes over.

  16. Viral Replication (2 possible cycles): Lytic and Lysogenic

  17. 1) Lytic Cycle • the replication process occurs in the cytoplasmof the host cell • 1. the virus’s genetic material enters the host cell • 2. the cell replicates the viral DNA or RNA • 3. the host cell makes new capsids and assembles new viral particles • 4. the host cell lyses (breaks open) and the new viruses leave the cell

  18. 2) Lysogenic Cycle • Virus’s genetic material enters the host cell nucleus and becomes part of the host cell’s chromosome(provirus) • In most cases the genes are not activated until later • Activation results in a continuation of the lytic cycle

  19. Chapter 2: Diversity: From Simple to Complex Section 2.1 Reproduction in Viruses UNIT 1

  20. Some Applications

  21. Video Clip – Flu Attack! How a virus invades your body (3:39) • http://www.youtube.com/watch?v=Rpj0emEGShQ

  22. Viral Replication http://www.mcgrawhill.ca/school/schoolGraphics/biology2_1.mpg

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