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A.Viruses

A.Viruses. Are Viruses Living or Non-living?.  Viruses are NOT living  They have some properties of life but not others  For example, viruses can be killed, even crystallized like table salt  However, they can’t maintain a constant internal state (homeostasis). What are Viruses?.

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A.Viruses

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  1. A.Viruses

  2. Are Viruses Living or Non-living?  Viruses are NOT living  They have some properties of life but not others For example, viruses can be killed, even crystallized like table salt  However, they can’t maintain a constant internal state (homeostasis).

  3. What are Viruses?  A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.

  4. B.Viral History

  5. Discovery of Viruses  Beijerinck (1897) coined the Latin name “virus” meaning poison

  6. Tobacco Mosaic Virus  Wendell Stanley (1935) crystallized sap from sick tobacco plants  He discovered viruses were made of nucleic acid and protein

  7. Smallpox  Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses  Deadly viruses are said to be virulent  Smallpox has been eradicated in the world today

  8. Viewing Viruses  Viruses are smaller than the smallest cell  Measured in nanometers  Viruses couldn’t be seen until the electron microscope was invented in the 20th century

  9. Size of Viruses

  10. C.Viral Structure

  11. Characteristics Contain a protein coat called the capsid  Have a nucleic acid core containing DNA or RNA Capable of reproducingonly when inside a HOST cell

  12. Characteristics  Some viruses are enclosed in an protective envelope  Some viruses may have spikes to help attach to the host cell  Most viruses infect only SPECIFIC host cells CAPSID DNA ENVELOPE SPIKES

  13. Characteristics  Some viruses cause disease  Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola  Some viruses may cause some cancers like leukemia MEASLES

  14. Influenza Virus T4 Bacteriophage Tobacco Mosaic Virus RNA DNA Head RNA Capsid Tail sheath Tail fiber Membrane envelope Surface proteins Capsid proteins

  15. Herpes Virus SIMPLEX I and II

  16. Adenovirus COMMON COLD

  17. Influenza Virus

  18. D.Bacteriophages

  19. Phages  Viruses that attack bacteria are called bacteriophage  Capsid contains DNA  Head & tail fibers made of protein

  20. phages  They infect E. coli , an intestinal bacteria Six small spikes at the base of a contractile tail are used to attach to the host cell  Inject viral DNA into cell

  21. E. Viral Replication

  22. Viral Attack  Viruses are very specific as to which species they attack  HOST specific  Humans rarely share viral diseases with other animals  Eukaryotic viruses usually have protective envelopes made from the host cell membrane

  23. 5 Steps of Lytic Cycle 1. Attachment to the cell 2. Entry (injection) of viral DNA or RNA 3. Replication of new viral proteins and nucleic acids 4. Assemblyof the new viruses 5. Release/Lysis of the new viruses into the environment (cell lysis)

  24. Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Tail 1 Attachment:Phage attaches to host cell. Base plate Pin Cell wall Plasma membrane 2 Entry:Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells

  25. Tail DNA 4 Assembly/Maturation:Viral components are assembled into virions. Capsid 5 Release/Lysis:Host cell lyses and new virions are released. Tail fibers

  26. Viral Latency  Some viruses have the ability to become dormant inside the cell They may remain inactive for long periods of time (years) Later, they activate to produce new viruses in response to some external signal HIV and Herpes viruses are examples

  27. Lysogenic Cycle 1.Phage DNA injected into host cell 2.Viral DNA joins host DNA forming a prophage 3.When an activation signal occurs, the phage DNA starts replicating

  28. Lysogenic Cycle, cont’d 4.Viral DNA (part of prophage) may stay inactive in host cell for long periods of time 5.Replicated during each binary fission 6.Over time, many cells form containing the prophages

  29. Lysogenic Cycle, cont’d 7.Once a prophage cell is activated, host cell enters the lytic cell 8.New viruses form a & the cell lyses (bursts) ACTIVESTAGE INACTIVE STAGE

  30. The Lysogenic Cycle

  31. Lysogenic virus examples… Some eukaryotic viruses remain dormant for many years in the nervous system tissues Chickenpox (caused by the virus Varicella zoster) is a childhood infection It can reappear later in life as shingles, a painful itching rash limited to small areas of the body SHINGLES

  32. …Lysogenic virus examples Herpes viruses also become latent in the nervous system A herpes infection lasts for a person’s lifetime Genital herpes (Herpes Simplex 2) Cold sores or fever blisters (Herpes Simplex1) SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY

  33. F. Retroviruses

  34. Characteristics of Retroviruses Contain RNA, not DNA Contain enzyme called Reverse Transcriptase When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell

  35. ENZYME

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