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Intro to Viruses

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  1. Intro to Viruses

  2. Learning Objectives - Viruses • Be able to • Describe the basic structure of a virus • Explain why viruses are classified as non-living

  3. What are Viruses? • Particles of nucleic acid, protein and in some cases, lipids • Reproduce by infecting living cells • Differ widely in terms of size and structure • Enter cells and use the machinery of the infected cell to produce more viruses

  4. Are Viruses Living? • According to the online Merriam-Webster Dictionary life is • “an organismic state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.” • Viruses are NOT living things • Complicated assemblies of molecules (including proteins, nucleic acids) • Cannot do anything on their own – they MUST enter a living cell • Without cells, viruses would not be able to multiply

  5. Virus Structure • Typical virus is made of • Core DNA or RNA • Surrounded by protein coat • (sometimes) contain layer of fat • Simplest viruses contain a few genes • Most complex can have > 100 genes

  6. Protein coat of a virus is called it’s capsid • Includes proteins that enable a virus to enter host cell

  7. Capsid proteins of viruses bind to receptors on cell’s surface • They “trick” the cell into allowing it inside • Once inside, the viral genes are expressed • Cell transcribes and translates the viral genetic information into viral capsid proteins

  8. Retrovirus

  9. What is it? • Contain RNA as their genetic material • Genetic information is copied backwards • From RNA to DNA (instead of DNA to RNA) • Retro = backward • Responsible for some types of cancers in animals, humans • Causes AIDS

  10. Infect cells • Produce a DNA copy of their RNA • Insert this DNA into host cell • Dormant before active • Production of new virus results in death of host cell