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Viral Structure

Viral Structure. www.onacd.ca. Virus Derived from the Latin word meaning toxin or poison. Is it a molecule or a microbe ?

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Viral Structure

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  1. Viral Structure www.onacd.ca

  2. VirusDerived from the Latin word meaning toxin or poison Is it a molecule or a microbe? Outside of the living cell, a virus is a lifeless chemical, and seems to carry out no life function of its own. However, once it invades a living cell, the virus displays an important trait that it shares will all living things…. It reproduces! Viruses occupy a position betweennon-living and living matter

  3. Types of Viruses Viruses are grouped into 3 types according to the cell type that they attack. Individual viruses will only attack a certain type of cell. This is called host specificity. Type #1 – Animal Viruses Type #2 – Plant Viruses Type #3 – Bacterial Viruses

  4. Animal Viruses Animal Viruses attack only animal cells The chicken pox virus (varicella zoster) is a highly contagious animal virus that is characterized by the spots it causes all over the body. varicella zoster virus

  5. Plant Viruses Plant Viruses attack only plant cells Tobacco Mosaic Virus (TMV) was the first virus to be discovered. It is an RNA virus that affects tobacco plants and other plants in the same family. It causes mottling and discoloration on the leaves. Tobacco Mosaic Virus

  6. Bacterial Viruses T4 Bacteriophage Bacterial Viruses attack only bacterial cells T4 Bacteriophage infects only E.Coli bacteria and is one of the largest bacterial viruses. T4 bacteriophage has a very distinct shape with a head,tail and tail fibres that help to anchor it onto a bacterial cell.

  7. General Structures of Viruses Helical (rod) DNA/RNA is found coiled within the hollow tube of the rod Can be short and rigid to long and flexible Complex Attack only bacterial cells. DNA/RNA is found within the head Unusual morphology that possess many structures Spherical / Icosohedral DNA/RNA is found coiled within the center icosahedron

  8. General Structure of a Bacteriophage Bacteriophage Capsid protein Collar Sheath Base Plate Spike Tail Fibres All viruses contain both a PROTEIN COAT (CAPSID PROTEIN) and either DNA or RNA

  9. Defining Characteristics of All Viruses • Non-cellular • Do not respire (breathe) • Do not respond to stimuli • Do not grow • Only reproduce once they are inside other living organisms or cells (parasitic) • Contain DNA or RNA or both • Contain a protein coat around the DNA or RNA • Can be stored inert (with reproducing) for long periods of time

  10. How are Viruses spread? Viruses can be spread in many different methods: • Via water droplets (tears, mucus) (ex. Cold, flu) • Via insects ( ex. Polio, hepatitis, TMV) • Via direct blood contact, other to child or person to person (ex. HIV, Herpes)

  11. Cool Virus Facts • Viruses range in size from about 20 to 400 nanometers in diameter. In perspective, a medium sized virus next to a flea is roughly the same as a human next to a mountain twice the size of Mount Everest • The study of viruses is known as virology and the scientists who study viruses are known as virologists Above: T4 Bacteriophages attacking a bacterial cell

  12. A few well known Viruses that can affect Humans…. Above: The influenza virus responsible for the Spanish flu that killed over 40 million people in 1918. Below: Human Pappiloma Virus (HPV) Above: The Ebola Virus Below: The Noravirus responsible for causing Norwalk epidemics in hospitals and cruise ships

  13. Viral Replication www.onacd.ca

  14. A closer look at the Bacteriophage life cycle… Bacteriophage (phage) with genetic material inside head • Step 1: Attachment • The tail fibres and base plate of the phage attach to specific surface receptors on the bacteria. • Note: Each type of phage is attracted to a certain type of surface receptor (ex. T4 bacteriophage is only attracted to receptors on E.coli cells.) Bacteria with a single ring of genetic material (in dark blue)

  15. Phage genetic material (viral DNA or RNA) Step 2 Step 1 • Step 2: Penetration / Entrance • The phage genetic material is injected into the bacterial cell. (Genetic material travels out of the head of the virus and through the tail into the bacterial cell.) The phage then disintegrates.

  16. A mix of the host bacterial DNA as well as the viral genetic material (DNA or RNA) Step 2 Step 1 Step 3 Step 3: Replication At this stage the viral genetic material will either integrate itself into the host DNA and enter the lysogenic pathway before it begins to replicate or it will begin to replicate within the bacterial cell.

  17. Lysogenic Pathway Step 2 Step 1 The Lysogenic Pathway This is a stage in which the viral DNA is basically lying dormant in the genetic material of the bacterial cell and replicating normally through binary fission along with the bacterium. This stage can last from minutes to years depending on the virus type.

  18. Lysogenic Pathway Step 2 Step 1 Step 4: Assembly The individual units of the phage are synthesized from the viral genetic material and brought together to form new phage particles. Step 4 Step 3

  19. Lysogenic Pathway Step 2 Step 1 Step 4 Step 3 Step 5 Step 5: Release of newly formed virusesThe bacterial cell lyses (dies and the cell wall/membrane breaks open) and the new virus particles are released to go out and infect other bacterial cells.

  20. Steps 1 through 5 are termed the Lytic Pathway Lysogenic Pathway Step 2 Step 1 Lytic Pathway Step 4 Step 3 Step 5

  21. A Electron Micrograph of bacteriophages attached to a bacterial cell wall.

  22. Human Leukemia cells infected by the Epstein Barr Virus

  23. Viruses and Disease Many human diseases are caused by viruses including the common cold, the flu, chickenpox and cold sores. Viruses are also the cause of more serious diseases such as Ebola, AIDS and SARS as well as some types of cancer. Some types of viruses like HIV and herpes simplex can lay dormant for years whereas others begin to cause cell death immediately until the point where the organism will start to suffer. (you get sick!)

  24. The human body’s basic lines of defense against viruses include… Primary lines of defense • Skin • Mucous Membranes • Cilia • Stomach acids • Tears (contain lysosomes that can destroy virus particles) How would each of the above help to protect the body from viral infections?

  25. Secondary Lines of Defense Phagocytic white blood cells Phagocytes leave the blood vessels, search out the viruses and engulf them. White Blood Cells can also make antibodies against viruses

  26. Antibodies attacking a virus

  27. Treatment and prevention • Anti-viral drugs are available to treat the symptoms of some viral diseases. They are not able to rid the body of the virus, only treat the symptoms and possible slow the replication of the virus. • The best treatment is prevention in the form of vaccines.

  28. How vaccines work • To produce a vaccine the virus must first be isolated • The virus is matured and allowed to reproduce under very carefully controlled conditions • The virus is chemically weakened so that it is no longer able to cause infection but the actual structure of the virus is still completely intact. • The weakened virus is injected into the organism to build up antibodies to the specific virus.

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