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VIRUSES

VIRUSES. Viruses are NOT Living…why?. Viruses do not have a cellular structure like: cytoplasm organelles cell membranes the ability to carry out life functions such as respiration, growth and development

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VIRUSES

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  1. VIRUSES

  2. Viruses are NOT Living…why? Viruses do not have a cellular structure like: • cytoplasm • organelles • cell membranes • the ability to carry out life functions such as respiration, growth and development • Thus, viruses are not living organisms and they are not classified in any “kingdom” of living things!

  3. Viruses are small - 10-300 nm (not mm)!

  4. Structure of a Virus All viruses consist of: • strands of DNA or RNA • surrounded by a protective protein coat – CAPSID • protects the virus from attack by the host cell enzymes • helps the virus attach itself to specific receptors on the host cell • The capsid shape is one way viruses are classified

  5. Viruses are classified by… • GENETIC MATERIAL: • DNA viruses (25%) contain DNA as their genetic material. • RNA (75%) viruses contain RNA as their genetic material. • What they are able to infect – animals, plants, fungi, tissues, species, etc. • What diseases they cause – e.g. adenoviruses infect adenoid tissue • The shape of and type of protein…

  6. Classifying Viruses (continued) • Shape is determined by the type and geometric arrangement of proteins in the capsid. • Polyhedral – i.e., polio virus • Spherical– i.e., HIV • Cylindrical – i.e., tobacco mosaic virus • Polyhedral head attached to protein tail and several tail fibres – i.e., T4 bacteriophage

  7. Bacteriophage Also known as a “phage” A virus that infects and destroys bacteria (cannot infect humans) Commonly used as the example to illustrate the lifecycles of viruses

  8. Viral Reproduction • Viruses depend on the metabolism of a eukaryotic and prokaryotic cell to replicate its DNA or RNA and the make protein coats for each newly formed virus. • Viruses can live in cells in 2 different ways: • Once attached to the host cell, the virus can inject its nucleic acid, build new viruses, then kill the host cell as the new viruses escape. Called the Lytic Cycle. • Or, the virus can enter the host cell but remain dormant for a period of time, without killing the host cell. This is the Lysogenic cycle.

  9. Virus Lifecycles Overview A) 5) E) B) 4) 3) C) & D)

  10. How does a Virus attach to a Host Cell? For a virus to replicate in either cycle, it must attach to a host cell When a virus’ proteins interlock with the receptor site, the virus is attached to its host cell The attachment process is like two pieces of a jigsaw puzzle fitting together Therefore viruses are very specific and can only infect one type of cell

  11. Lytic Cycle: A Viral Replication Process Attachment: The Bacteriophage Virus attaches to the host cell Entry:The virus injects its nucleic acid into the bacterial cell. *At this point the viral DNA/RNA an be incorporated into the host cell’s genome and enter the lysogenic cycle, OR…

  12. Lytic Cycle: A Viral Replication Process Replication :The host’s machinery replicates the virus’ nucleic acid and proteins Assembly: New virus parts are assembled using host cell machinery Lysis and Release: (8)The host cell breaks open and new viruses are released and the host cell = is killed (lysis/lytic)

  13. In 30 mINutes 200 new viruses can be produced, ready to spread to neighbouring cells

  14. The Lysogenic Cycle: Begins the same way as the Lytic Cycle; the virus attachment to the host cell and its nucleic acid is injected and has entry into the cell. Then the viral DNA is integrated into the host cell's chromosomes, forming aProvirus The virus remains dormantand when the host cell divides through the process of mitosis, it replicates the viral DNA provirus along with its own DNA. This continues for many generations with the viral DNA undetected. Every descendant of the host cell will carry a copy of the provirus in its chromosomes. This cycle does not kill its host cell. Good examples: cold sores (herpes) and chickenpox (shingles) – see article

  15. This LYSOGENIC CYCLE can continue for years, with no harm to the host. • However, at any time the provirus can separate from the host chromosomes and complete the more damaging LYTIC CYCLE • UV rays, chemicals, stress etc. can induce the virus to return to the lytic cycle.

  16. The Lysogenic Cycle Overview

  17. RNA Viruses: • Many Viruses, including HIV, are RNA viruses • This means their only nucleic acid is RNA • They must convert their RNA to DNA • The RNA virus with the most complex replication cycle is the Retrovirus • The Retrovirus - uses reverse transcriptase to make DNA from viral RNA • the retroviral DNA is then integrate its DNA into into the host cell's chromosome • It then follows the lysogenic cycle, undetected.

  18. Reverse Transcriptase: • Is an enzyme carried in the capsid of a retrovirus that helps produce viral DNA from viral RNA • If this enzyme is found in a person, it is evidence for infection by a retrovirus

  19. Retrovirus Cycle:

  20. Examples of DNA/RNA Viruses

  21. How Can Viral Diseases Be Prevented and Treated? • Good hygiene • Avoid contact with contaminated food, water, fecal material or body fluids. • Wash hands frequently. • Vaccines • Stimulate natural defenses with in the body. • Contain a component of or a weakened or killed virus particles. • Are developed for many once common illnesses such as smallpox, polio, mumps, chicken pox. • Not available for all viruses. • Anti-viral drugs (but not antibiotics) • Available for only a few viruses. • Inhibit some virus development and/or relieve symptoms. • *Some viruses have been linked to cancer

  22. Discuss – what do you know about these viral diseases? • Common cold • Influenza (the Flu) • Avian Flu (H5N1) • Swine Flu (H1N1) • West Nile • Ebola • Smallpox • Cowpox • SARS • Norwalk • HIV

  23. Historical Influenza Pandemics Recent Influenza Pandemics • What is the longest time period between pandemics? • When should the next one occur? Was this “the one”? If so, we got “lucky”

  24. Human Immunodeficiency Virus(HIV) • HIV infects white blood cells in humans • The infected cells still function normally • Because the viral genetic material is a provirus that only produces a small number of new viruses at a time • An infected person will not appear sick • Can infect others with the virus through body fluids • Most people with HIV will get AIDS • Over time, more white blood cells are infected and killed • White Blood cells are essential to our immune system • Their destruction reduces the body’s ability to protect itself from other viruses

  25. SARS (severe acute respiratory syndrome) • The incubation period ranges from 2 to 10 days (or even 14 days). • The initial indication of infection is a fever of 38 °C or more, chills, headache, muscle soreness, and a general feeling of discomfort are also common. • A dry, unproductive cough develops after 3 to 7 days. • Eventually this results in hypoxemia (a condition characterized by a reduced concentration of oxygen in the blood). • Approximately 10 to 20% of infected patients require some type of assistance in breathing either through intubation or mechanical ventilation.

  26. EbolaElectron micrograph of Zaire Ebola virus, first photo ever taken, on 10/13/1976 by Dr. F.A. Murphy (160,000 x magnification). • The incubation period ranges from 2 to 21 days. • Ebola virus is transmitted by contact with blood, feces or body fluids from an infected person or by direct contact with the virus, as in a laboratory. • The initial symptoms are usually high fever, headache, muscle aches, stomach pain, and diarrhea (there may also be sore throat, hiccups, and red and itchy eyes). • The symptoms that tend to follow include: • within a week, a raised rash • bleeding from the mucous membranes like the mouth, nose (epistaxis), eyes (conjunctival hemorrhages) and rectum • spitting up blood from the lungs (hemoptysis) • vomiting it up from the stomach (hematemesis) • finally chest pain, shock, and death.

  27. Virus’ link to Cancer: • Some viruses have been linked to certain cancers in humans and animals • Viruses can disrupt the normal growth and division of cells in a host • This causes abnormal growth and creates tumors

  28. Plant Viruses: There are more than 400 plant viruses Plant viruses can cause stunted growth and yield losses in their host plants. The first virus to be identified as a plant virus was the Tobacco Mosaic Virus in 1892 Plant viruses do not undergo lytic or lysogenic phases Plant viruses are named according to their host plant. Not all viral plant diseases are fatal or even harmful.

  29. Viruses and Biotechnology Biotechnology refers to technology used to manipulate DNA. The procedures are often referred to as genetic engineering. DNA is the genetic material of all living organisms and all organisms use the same genetic code. Genes from one kind of organism can be put into another kind of organism.  A virus’s DNA can be removed, another piece of DNA is spliced onto the viral DNA, this is then put back into the virus. This virus is then sent into a host cell. The virus then makes multiple copies and each new virus has the new gene the researchers want copied.

  30. Homework Fun • Chapter 1 quiz tomorrow • Do the ch.1 practice test and SA on myclass • Finish Ch. 1 review in textbook pg 45

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