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Virus Notes

Virus Notes. Basic Definition. parasitic. acellular. Submicroscopic. Viruses : Submicroscopic, parasitic, acellular entity composed of a nucleic acid core surrounded by a protein coat. Below the resolution of a microscope Relies on a host Does not have the properties of cellular life

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Virus Notes

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  1. Virus Notes

  2. Basic Definition parasitic acellular Submicroscopic • Viruses: Submicroscopic, parasitic, acellular entity composed of a nucleic acid core surrounded by a protein coat. • Below the resolution of a microscope • Relies on a host • Does not have the properties of cellular life • Viruses are measured in nanometers • 0.000000001m or 10-9

  3. Virus Bacterium Animalcell Animal cell nucleus 0.25 m Comparing the size of a virus, a bacterium, and an animal cell

  4. Capsomereof capsid Membranousenvelope RNA Capsomere DNA Head Capsid Tail sheath DNA RNA Tail fiber Glycoprotein Glycoprotein 80  225 nm 18  250 mm 80–200 nm (diameter) 70–90 nm (diameter) 50 nm 20 nm 50 nm 50 nm (d) Bacteriophage T4 (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses Viral Shapes and structure • Although viruses can have several shapes, all have at least two parts: • An outer capsid made of proteins. • Genetic material (DNA or RNA – never both)

  5. What is a bacteriophage? T4 bacteriophages infecting an E. coli cell Protein coat • A virus that invades bacteria. It consists of a DNA core and a protein coat DNA

  6. Why aren’t viruses considered alive? • Viruses are acellular (not cells) • Viruses have no organelles to take in nutrients or use energy. • Viruses cannot make proteins. • Viruses cannot move. • Viruses cannot replicate on their own.

  7. Virus Reproduction Viruses reproduce by infecting other cells. Two types of viral infections: 1. Lytic Infection 2. Lysogenic Infection

  8. What are the steps of a lytic infection? Step 5: New viruses “lyse” the host cell and are released for further infection Step 3: Replication of viral DNA and Synthesis of Protein Capsule using cellular “machinery” – cellular enzymes, ribosomes, etc. Step 1: Attachment of virus to host cell Step 4: Assembly of new viruses inside host cell Step 2: Injection of viral DNA into cell

  9. Characteristics of Lytic Infections • Fast acting • Symptoms emerge within 24 – 48 hours • Examples – influenza, west-nile

  10. The Lysogenic Infection Step 1: Virus attaches and inserts its DNA inside host Step 2: Viral DNA attaches to the host DNA (prophage DNA) Step 3: The viral DNA lies “dormant” and the viral DNA replicates each time the cell divides Step 4: Stress or other “factors” causes the infection to progress to the “lytic” phase

  11. Characteristics of Lysogenic Infections • Slow Acting - Viral DNA can lie “dormant” for many years, hidden within prophage DNA • The host are “symptom-free” during dormancy • Infection is fast acting when the infection progresses to the lytic phase 4. Example: HIV

  12. What is a retrovirus? • A retrovirus is a virus with RNA rather than DNA for its genetic material. • These viruses carry an enzyme to create DNA from their RNA. • The viral DNA then integrates into a chromosome. (Just kidding… here’s a real retrovirus!)

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