The Impact of Viruses and Bacteria: Understanding Their Role in Disease and Health

1. Viruses and Bacteria

2. Not So HarmlessIn The News

3. Viruses • Infectious agents • No cell structure • Contain DNA or RNA • Non-living • Obligate parasites

4. Properties of Viruses • Can infect all forms of life • Many infect only one species

5. Virus Size • Extremely small • Comparison • Human red blood cell = 10,000 nm • Plasma membrane width 30 nm

6. Virus Structure • Nucleic acid core • DNA (double or single stranded) • RNA

7. Virus Structure • Capsid = protein covering • Some have envelope over capsid

8. Tobacco Mosaic Virus

9. Herpes Virus

10. Replication of Viruses • Cannot multiply outside cells • Uses cell organelles to multiply • Process is called lytic cycle • Lysogenic cycle • Long term relationship of cell & virus • Viral nucleic acid replicates as cell multiplies

12. Ways Viruses Cause Disease • Can initiate cancer • Can take over cell function

13. Cancer & Viruses • Some viruses initiate cancer • Virus causes cell changes • Virus does not “carry” cancer

15. Viruses as Pathogens • Disrupt cell functions • Use cells to make more virus

16. Acute infection Rapid onset Run a course Subside Examples Common cold Influenza Measles Mumps Latent Infection Infective agent present Not manifesting disease Causes latent infections Examples Herpes HIV Viral Infections

17. Genital Herpes • Common STD • More than 1 in 5 age 12 & over in U.S. • Caused by herpes simplex virus • Develops a few days after sexual contact • Spreads when virus is active • Lesions develop • Latent infections

19. Prions & Viroids • Infectious agents • Simpler than viruses

20. Prions • Proteins that cause disease • Only infectious agent with no nucleic acid • Examples: • Bovine spongiform encephalopathy • mad cow disease • Creutzfeldt-Jacob disease

21. Healthy Brain Tissue Prion-infected Brain Tissue

22. Viroids • Small strands of RNA • No protein coats • Replicated in host cells • Known to cause plant diseases

23. Bacteria • Prokaryotic cells • Some harmful, some helpful • Present virtually everywhere

25. Characters of Bacteria • No membrane-bound nucleus • No membrane-bound organelles

27. Modes of Nutrition in Bacteria • Photoautotrophic • Chemoautotrophic • Hetrotrophic

28. Photoautotrophs • Produce food via photosynthesis • Green & purple bacteria, cyanobacteria • Cyanobacteria probably oxygenated Earth’s atmosphere

29. Chemautotrophs • Energy from inorganic molecules • Manufacture growth factors • Carbohydrates • Fats • Proteins • Nucleic acids • Important in nitrogen cycling

30. Heterotrophs • Feed on other organisms • Play key role in carbon cycling • Many bacteria are decomposers • Release CO2 used by photosynthesizers

31. Archaea • Prokaryotic cells • Not bacteria • None cause disease • Often in harsh habitats

33. Reproduction in Bacteria • Asexual binary fission

34. Bacterial Disease • Attach to cells • Cause tissue damage • Some plant diseases • Many human diseases

36. Syphilis • Caused by spiral bacterium • Sexually transmitted • Curable with penicillin • Can cause death if untreated

37. Stages of Syphilis • Primary • Hard chancre sore • Becomes painful • Secondary • 6 weeks – months • Dispersed thru body • Lesions at other sites

38. Stages of Syphilis • Latent stage • No symptoms • May last a lifetime • Tertiary stage • New lesions – tumor-like • Paralysis and death

39. Gonorrhea • Sexually transmitted • May exhibit few symptoms • Can cause sterility

40. Clamydia • Most prevalent STI • Can lead to sterility • Grow only within other cells • Bacteria is “energy parasite”