Virus

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Virus

  1. 1. CHARACTERISTICS OF VIRUSES
  2. 2. <ul><li>Many common illnesses are caused by viruses. </li></ul><ul><li>Viruses are easily killed by drugs such as antibiotics. </li></ul><ul><li>Once you have contracted a specific virus, you will not get sick from this virus again because of the antibodies produced in your body. </li></ul><ul><li>Many diseases caused by viruses can be avoided through vaccination. </li></ul><ul><li>Viruses are very fragile and cannot live on surfaces outside fo the human body. </li></ul><ul><li>Viruses have the ability to change themselves, or mutate, over time. </li></ul>Pre-Quiz (True or False)
  3. 3. Pre-Quiz Continued <ul><li>7. Viral illnesses cannot be transferred from animals to people. </li></ul><ul><li>8. The only way to transmit viruses is through close physical contact with an infected person. </li></ul><ul><li>9. Viruses can become resistant to drugs used to treat them. </li></ul><ul><li>10. One of the best ways to prevent the spread of viral diseases is frequent, thorough hand washing. </li></ul>
  4. 4. Are Viruses Living or Non-living? <ul><li>Biologists consider viruses to be non-living because: </li></ul><ul><ul><li>Are not cells </li></ul></ul><ul><ul><li>Do not use energy to grow or respond to their surroundings </li></ul></ul><ul><ul><li>Cannot make food, take in food, or produce wastes </li></ul></ul><ul><ul><li>Viruses do not respond to stimuli in the environment such as light, temperature, chemicals, sound, gravity, heat, water and pressure. </li></ul></ul><ul><li>They can only multiply like other organisms but only inside a living cell </li></ul>
  5. 5. What are Viruses? Definition- <ul><li>Viruses are noncellular particles made up of genetic material and protein that can invade living cells. </li></ul><ul><li>Small, non-living, invades and reproduces inside a living cell </li></ul><ul><li>1 virus- can produce thousands of new viruses </li></ul>
  6. 6. Discovery of Viruses <ul><li>Beijerinck (1897) coined the Latin name “ virus ” meaning poison </li></ul><ul><li>He studied filtered plant juices & found they caused healthy plants to become sick </li></ul>
  7. 7. Tobacco Mosaic Virus <ul><li>Wendell Stanley (1935) crystallized sap from sick tobacco plants </li></ul><ul><li>He discovered viruses were made of nucleic acid and protein </li></ul>
  8. 8. Smallpox <ul><li>Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses </li></ul><ul><li>Deadly viruses are said to be virulent </li></ul><ul><li>Smallpox has been eradicated in the world today </li></ul>
  9. 9. How Big is a Virus? <ul><li>Viruses are very small – smaller than the smallest cell . </li></ul><ul><ul><li>They may vary in size from 20-400 nm. </li></ul></ul><ul><ul><ul><li>Measured in nanometers (nm = one billionth of a meter) </li></ul></ul></ul><ul><ul><ul><li>one millionth of an inch </li></ul></ul></ul><ul><ul><ul><li>1000x smaller than bacteria </li></ul></ul></ul><ul><ul><ul><li>Bacteria = much smaller than a human cell </li></ul></ul></ul>
  10. 10. Characteristics <ul><li>Non living structures </li></ul><ul><li>Non-cellular </li></ul><ul><li>Contain a protein coat called the capsid </li></ul><ul><li>Have a nucleic acid core containing DNA or RNA (one or the other - not both) </li></ul><ul><li>Capable of reproducing only when inside a HOST cell </li></ul>
  11. 11. Characteristics <ul><li>Some viruses are enclosed in an protective envelope </li></ul><ul><li>Some viruses may have spikes to help attach to the host cell </li></ul><ul><li>Most viruses infect only SPECIFIC host cells </li></ul>CAPSID ENVELOPE DNA SPIKES
  12. 12. Characteristics <ul><li>Outside of host cells, viruses are inactive </li></ul><ul><li>Lack ribosomes and enzymes needed for metabolism </li></ul><ul><li>Use the raw materials and enzymes of the host cell to be able to reproduce </li></ul>EBOLA VIRUS HIV VIRUS
  13. 13. Characteristics <ul><li>Viruses cause many common illnesses diseases </li></ul><ul><li>Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola, the “flu,” chicken pox, measles, polio, </li></ul><ul><li>and hepatitis </li></ul><ul><li>Some viruses may cause some cancers like leukemia </li></ul><ul><li>Virus-free cells are rare </li></ul>MEASLES
  14. 14. What do Viruses look like? <ul><li>Viruses are unusual and different from other things in nature. </li></ul><ul><li>Viruses come in a variety of shapes </li></ul><ul><ul><li>Some are rod-shaped, round-shaped, tadpole-shaped, many-sided, helical, cube-like and so on. </li></ul></ul><ul><li>Some may be helical shape like the Ebola virus </li></ul><ul><li>Some may be polyhedral shapes like the influenza virus </li></ul><ul><li>Others have more complex shapes like bacteriophages </li></ul><ul><ul><li>THEY JUST DON’T LOOK LIKE OTHER THINGS! </li></ul></ul>
  15. 15. Types of Viruses: Helical Viruses
  16. 16. Polyhedral Viruses
  17. 17. Complex Viruses
  18. 18. Viral Taxonomy <ul><li>Family names end in - viridae </li></ul><ul><li>Genus names end in - virus </li></ul><ul><li>Viral species: A group of viruses sharing the same genetic information and ecological niche (host). </li></ul><ul><li>Common names are used for species </li></ul><ul><li>Subspecies are designated by a number </li></ul>
  19. 19. Viral Taxonomy Examples <ul><li>Herpesviridae </li></ul><ul><li>Herpesvirus </li></ul><ul><li>Human herpes virus 1, HHV 2, HHV 3 </li></ul><ul><li>Retroviridae </li></ul><ul><li>Lentivirus </li></ul><ul><li>Human Immunodeficiency Virus 1, HIV 2 </li></ul>
  20. 20. <ul><li>RNA or DNA Virus </li></ul><ul><li>Do or do NOT have an envelope </li></ul><ul><li>Capsid shape </li></ul><ul><li>HOST they infect </li></ul>Used for Virus Identification
  21. 21. Herpes Virus SIMPLEX I and II
  22. 22. Adenovirus COMMON COLD
  23. 23. Influenza Virus
  24. 24. Chickenpox Virus
  25. 25. Papillomavirus – Warts!
  26. 26. Bacteriophages
  27. 27. Phages <ul><li>Viruses that attack bacteria are called bacteriophage or just phage </li></ul><ul><li>T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails </li></ul>
  28. 28. T-phages <ul><li>The most commonly studied T-phages are T4 and T7 </li></ul><ul><li>They infect E. coli , an intestinal bacteria </li></ul><ul><li>Six small spikes at the base of a contractile tail are used to attach to the host cell </li></ul><ul><li>Inject viral DNA into cell </li></ul>
  29. 29. Retroviruses
  30. 30. Characteristics of Retroviruses <ul><li>Contain RNA, not DNA </li></ul><ul><li>Family Retroviridae </li></ul><ul><li>Contain enzyme called Reverse Transcriptase </li></ul><ul><li>When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell </li></ul><ul><li>Examples: HIV, the AIDS virus, Feline </li></ul><ul><li>Leukemia Virus </li></ul>
  31. 31. Viroids <ul><li>Small, circular RNA molecules without a protein coat </li></ul><ul><li>Infects plants </li></ul><ul><li>Potato famine in Ireland </li></ul>
  32. 32. Prion Diseases <ul><li>Prions have no DNA or RNA </li></ul><ul><li>Prions form insoluble deposits in the brain </li></ul><ul><li>Causes neurons to rapidly degeneration. </li></ul><ul><li>Mad cow disease (bovine spongiform encephalitis: BSE) is an example </li></ul><ul><li>People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies </li></ul>
  33. 33. Viral Attack <ul><li>Viruses are very specific as to which species they attack </li></ul><ul><li>HOST specific </li></ul><ul><li>A vector is a host that transfers viruses to another organism </li></ul><ul><li>Example – West Nile Virus is spread through mosquitoes </li></ul><ul><li>Humans rarely share viral diseases with other animals </li></ul><ul><li>Eukaryotic viruses usually have protective envelopes made from the host cell membrane </li></ul>
  34. 34. 5 Steps of Lytic Cycle <ul><li>1. Attachment to the cell </li></ul><ul><li>2. Penetration (injection) of viral DNA or RNA </li></ul><ul><li>3. Replication (Biosynthesis) of new viral proteins and nucleic acids </li></ul><ul><li>4. Assembly (Maturation) of the new viruses </li></ul><ul><li>5. Release of the new viruses into the environment (cell lyses) </li></ul>
  35. 35. Bacteriophage Replication <ul><li>Bacteriophage inject their nucleic acid </li></ul><ul><li>They lyse (break open) the bacterial cell when replication is finished </li></ul>
  36. 36. INFECTION
  37. 37. Viral Latency <ul><li>Some viruses have the ability to become </li></ul><ul><li>dormant inside the cell </li></ul><ul><li>Called latent viruses </li></ul><ul><li>They may remain inactive for long periods </li></ul><ul><li>of time (years) </li></ul><ul><li>Later, they activate to produce new </li></ul><ul><li>viruses in response to some external </li></ul><ul><li>signal </li></ul><ul><li>HIV and Herpes viruses are examples </li></ul>
  38. 38. Lysogenic Cycle <ul><li>Phage DNA injected into host cell </li></ul><ul><li>Viral DNA joins host DNA forming a prophage </li></ul><ul><li>When an activation signal occurs, the phage DNA starts replicating </li></ul><ul><li>Viral DNA (part of prophage) may stay inactive in host cell for long periods of time </li></ul>
  39. 39. Latency in Eukaryotes <ul><li>Some eukaryotic viruses remain dormant for many years in the nervous system tissues </li></ul><ul><li>Chickenpox (caused by the virus Varicella zoster ) is a childhood infection </li></ul><ul><li>It can reappear later in life as shingles, a painful itching rash limited to small areas of the body </li></ul>SHINGLES
  40. 40. Latency in Eukaryotes <ul><li>Herpes viruses also become latent in the nervous system </li></ul><ul><li>A herpes infection lasts for a person’s lifetime </li></ul><ul><li>Genital herpes (Herpes Simplex 2) </li></ul><ul><li>Cold sores or fever blisters (Herpes Simplex1) </li></ul>SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY
  41. 41. HOST SPECIFICITY <ul><li>All kingdoms can be infected by viruses </li></ul><ul><li>Viruses that infect organisms of one kingdom are not able to infect organisms of another kingdom </li></ul><ul><li>Viruses can infect species of organisms that are closely related or not closely related (some viral diseases can be passed from different species) </li></ul><ul><li>Viruses can even be species specific (only passed within the same species) </li></ul><ul><li>Spread is specific to the type of virus </li></ul><ul><li>-Carrier organisms, the air, direct transfer of body fluids </li></ul><ul><li>-Surfaces on which body fluids have dried </li></ul>
  42. 42. PARASITISM <ul><li>Viruses are parasites. </li></ul><ul><ul><li>A parasite is an organism that depends upon another living organism for its existence in such a way that it harms that organism. </li></ul></ul><ul><ul><li>Viruses must infect living cells in order to carry out their functions of growth and reproduction. </li></ul></ul><ul><ul><li>Viruses depend upon their hosts for respiration, nutrition and all the other functions that occur in living things. </li></ul></ul>
  43. 43. Vaccines <ul><li>An attenuated virus is a weakened, less vigorous virus </li></ul><ul><li>“ Attenuate&quot; refers to procedures that weaken an agent of disease (heating) </li></ul><ul><li>A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus </li></ul><ul><li>Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness </li></ul>
  44. 44. Viral illness <ul><li>Treatment of viral disease include vaccination, vector control, and drug therapy </li></ul><ul><li>Drug therapy does NOT work very well </li></ul><ul><li>Vaccination and vector control are the most successful way to beat viruses </li></ul><ul><li>Vaccination works because once you are exposed to and overcome a virus your immune system creates antibodies that will immediately attack the virus if it shows up again </li></ul><ul><li>Hand-washing is effective against bacterial diseases and viral diseases </li></ul>
  45. 45. Other Viral Treatments <ul><li>Interferon are naturally occurring proteins made by cells to fight viruses </li></ul><ul><li>Genetic altering of viruses (attenuated viruses) </li></ul><ul><li>Antiviral drugs (AZT) </li></ul><ul><li>Protease inhibitors – prevent capsid formation </li></ul>copyright cmassengale
  46. 46. Reducing the Risk <ul><li>Cover mouth/nose when you sneeze of cough </li></ul><ul><li>Wash hands frequently </li></ul><ul><li>Avoid contact with the body fluids </li></ul><ul><li>Not foolproof but reduces the risks </li></ul>

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