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Viruses

This chapter explains the relationship between bacteria, protists, and viruses, focusing on the structure and classification of viruses. It also covers viral diseases, including common ones like the cold and flu, and discusses viral infection processes such as lytic and lysogenic infections. The chapter concludes with information on emerging diseases and viroids and prions.

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Viruses

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  1. Viruses Chapter 24

  2. Standards • Standard 1: Cells • CLE 3216.1.6 • Describe the relationship between bacteria, protists, and viruses and their host cells • Prokaryotes

  3. Viruses • NOT living (don’t meet all requirements) • Ex: Don’t grow and develop • Needs a host to survive • Cannot carry out cellular functions • Core of DNA or RNA surrounded by protein coat • Reproduce only by infecting living cells

  4. Viral Diseases • Viruses that cause disease attack and destroy cells • Cannot be treated with antibiotics (maybe over the counter medicines) • Vaccines work if used before virus is contracted

  5. Common Viral Diseases • Common cold • Flu • AIDS • Chicken Pox/Shingles • Hepatitis B • West Nile Virus

  6. Virus Structure • Core filled with genetic material inside • Capsid =protein coat • Proteins attach to cell “tricking” it into letting the virus in • Viral genes are copied • Host cell dies • Bacterophage = virus that only infects bacteria

  7. Classification of Viruses • Have RNA vs DNA as their genome • Double stranded vs Single stranded • Linear vs Circular

  8. Viral Infection • 2 viral infection processes: • Lytic infection - host cell bursts • Lysogenic infection - virus remains inactive inside of host for periods of time

  9. Lytic Infection • Virus DNA is injected into host cell • Cell begins to copy virus DNA, then make virus proteins • Virus proteins break down host cell and uses it to copy more viruses • Cell finally bursts (lyses)

  10. Lysogenic Infection • Virus DNA is injected into host cell’s DNA • DNA is replicated with included viral DNA • Cell does not lyse - virus remains inactive for period of time • Then enters lytic cycle when inactivation is over

  11. Retrovirus • Virus with RNA as genetic material • Retro = backwards • Copies RNA into DNA instead of DNA to RNA • Ex: AIDS

  12. Emerging Disease • Illness caused by new or reappearing agents that typically exist in animal populations • Ex: Ebolo virus

  13. Viroids and Prions • Viroids: smallest known particles known to replicate - Infect plants • Prions: Infectious protein particles - causes degenerative brain diseases Ex: Mad cow disease

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