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Viruses

Explore the world of viruses, their characteristics, and how they depend on living cells for reproduction. Learn about different viruses like H1N1, HIV, Ebola, and their size comparison to bacteria. Discover the basic structure of viruses and the ways they enter host cells. Understand viral replication cycles, lytic and lysogenic, and their impact on the infected organisms.

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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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