1. © 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Chapter 13 Characterizing and Classifying Viruses and Prions

2. Characteristics of Viruses Virus –Minuscule, acellular infectious agent having either DNA or RNA –Causes many infections of humans, animals, plants, and bacteria –Causes most of the diseases that plague the industrialized world © 2012 Pearson Education Inc.

3. Characteristics of Viruses Cannot carry out any metabolic pathway Neither grow nor respond to the environment Cannot reproduce independently Recruit the cell’s metabolic pathways to increase their numbers No cytoplasmic membrane, cytosol, organelles, but some have a membrane-like envelope. Have extracellular and intracellular state © 2012 Pearson Education Inc.

4. Characteristics of Viruses Extracellular State –Called virion –Protein coat (capsid) surrounding nucleic acid –Some have phospholipid envelope –Outermost layer provides protection and recognition sites for host cells Intracellular State –Capsid removed –Virus exists as nucleic acid © 2012 Pearson Education Inc.

5. Figure 13.1 Virions-overview

6. Characteristics of Viruses Genetic Material of Viruses –Show more variety in nature of their genomes than do cells –Primary way scientists categorize and classify viruses –May be DNA or RNA, but never both –Much smaller than genomes of cells © 2012 Pearson Education Inc.

7. Figure 13.2 The relative sizes of genomes Partial genome of E. coli Viral genome

8. Characteristics of Viruses Hosts of Viruses –Most viruses infect only particular host’s cells –Affinity of viral surface proteins for proteins on host cell –May be so specific they infect only particular kind of cell in a particular host –Bacteriophages are viruses that infect bacteria. © 2012 Pearson Education Inc.

9. Figure 13.3 Hosts of viral infections-overview

10. Figure 13.4 Sizes of selected virions Red blood cell (10,000 nm in diameter) E. coli (bacterium) (1000 nm  3000 nm) Poliovirus (30 nm) Bacteriophage MS2 (24 nm) Bacteriophage T4 (50 nm  225 nm) Smallpox virus (200 nm  300 nm) Tobacco mosaic virus (15 nm  300 nm) Bacterial ribosomes (25 nm)

11. Characteristics of Viruses Capsid Morphology –Capsids –Provide protection for viral nucleic acid –Means of attachment to host’s cells © 2012 Pearson Education Inc.

12. Figure 13.5 The shapes of virions-overview

13. Figure 13.6 Bacteriophage T4-overview

14. Characteristics of Viruses The Viral Envelope –Acquired from host cell during viral replication or release –Envelope is portion of membrane system of host –Composed of phospholipid bilayer and proteins –Envelope’s proteins often play role in host recognition © 2012 Pearson Education Inc.

15. Figure 13.7 Enveloped virion-overview

16. Viral Replication Dependent on hosts’ organelles and enzymes to produce new virions Lytic replication –Replication cycle usually results in death and lysis of host cell Stages of lytic replication cycle –Attachment –Entry –Synthesis –Assembly –Release © 2012 Pearson Education Inc.

17. Figure 13.8 The lytic replication cycle in bacteriophages-overview Attachment Tail sheath Bacteriophage genome Outer membrane Peptidoglycan Cytoplasmic membrane Bacterial chromosome Attachment Entry Lytic replication cycle of bacteriophage Release Assembly Phage proteins Entry Phage DNA Bacterial chromosome degraded Synthesis Assembly Base Tail Sheath DNA Capsid Mature head Tail fibers Mature virion

18. Viral Replication Lysogeny –Modified replication cycle –Infected host cells grow and reproduce normally for generations before they lyse –Virus gets inserted into host cell DNA. © 2012 Pearson Education Inc.

19. Figure 13.11 The lysogenic replication cycle in bacteriophages: phage lambda and E. coli Attachment Lambda phage Entry Lytic cycle Release Assembly Induction Synthesis Prophage in chromosome Further replications and cell divisions Lysogeny Replication of chromosome and virus; cell division

20. Viral Replication Replication of Animal Viruses –Synthesis of animal viruses –Requires different strategy depending on its nucleic acid –DNA viruses often enter the nucleus –RNA viruses often replicate in the cytoplasm © 2012 Pearson Education Inc.

21. Figure 13.14 The process of budding in enveloped viruses Enveloped virion Budding of enveloped virus Viral capsid Viral glycoproteins Cytoplasmic membrane of host

22. Viral Replication Replication of Animal Viruses –Latency of animal viruses –When animal viruses remain dormant in host cells –May be prolonged for years with no viral activity –Some latent viruses do not become incorporated into host chromosome –Herpesvirus –Incorporation of provirus into host DNA is permanent © 2012 Pearson Education Inc.

23. Figure 13.17 Viral plaques in a lawn of bacterial growth on the surface of an agar plate Bacterial lawn Viral plaques

24. Are Viruses Alive? Some consider them complex pathogenic chemicals Others consider them the least complex living entities –Use sophisticated methods to invade cells –Have the ability to take control of their host cell –Are able to replicate themselves © 2012 Pearson Education Inc.

25. Other Parasitic Particles: Viroids and Prions Characteristics of Prions –Proteinaceous infectious agents. –Prion diseases –Fatal neurological degeneration and loss of brain matter –Large vacuoles form in brain –Characteristic spongy appearance –Spongiform encephalopathies (mad cow disease) –Prions are extremely difficult to kill. Must be incinerated. © 2012 Pearson Education Inc.

26. Figure 13.23 The brain of a sheep with the prion disease called scrapie Vacuole

27. © 2012 Pearson Education Inc. Lecture prepared by Mindy Miller-Kittrell North Carolina State University Chapter 12 Characterizing and Classifying Eukaryotes

28. General Characteristics of Eukaryotic Organisms We will look at a few major groups –Fungi –Protists—protozoa or animal-like protists –Animals—helminths (worms) and arthopod vectors Include both human pathogens and organisms vital for human life © 2012 Pearson Education Inc.

29. General Characteristics of Eukaryotic Organisms Reproduction in Eukaryotes –More complicated than reproduction in prokaryotes –Eukaryotic DNA packaged as chromosomes in the nucleus –Have variety of methods of asexual reproduction –Many reproduce sexually by forming gametes and zygotes –Algae, fungi, and some protozoa reproduce both sexually and asexually © 2012 Pearson Education Inc.

30. Protozoa Diverse group defined by three characteristics –Eukaryotic –Unicellular –Lack a cell wall Motile by means of cilia, flagella, and/or pseudopodia –Except subgroup, apicomplexans © 2012 Pearson Education Inc.

31. Protozoa Distribution of Protozoa –Require moist environments –Most live in ponds, streams, lakes, and oceans –Critical members of plankton –Others live in moist soil, beach sand, and decaying organic matter –Very few are pathogens –All produce trophozoites (vegetative form); some produce cysts © 2012 Pearson Education Inc.

32. Figure 12.5 Contractile vacuole-overview Closed vacuole Open vacuole

33. Protozoa Nutrition of Protozoa –Most are chemoheterotrophic –Obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of host © 2012 Pearson Education Inc.

34. Figure 12.8b Trypanosoma Kinetoplast Nucleus

35. Fungi Chemoheterotrophic Have cell walls typically composed of chitin Do not perform photosynthesis –Lack chlorophyll © 2012 Pearson Education Inc.

36. Fungi The Significance of Fungi –Decompose dead organisms and recycle their nutrients –Help plants absorb water and minerals –Used for food and in manufacture of foods and beverages –Produce antibiotics –Serve as important research tools –30% cause diseases of plants, animals, and humans –Can spoil fruit, pickles, jams, and jellies © 2012 Pearson Education Inc.

37. Did you know? The largest organism on Earth is a fungus. Wow.

38. Fungi as Infectious Agents Molds (multicellular) and yeasts (unicellular) are widely distributed in air, dust, fomites and normal flora. Humans are relatively resistant. Fungi are relatively nonpathogenic. Of the 100,000 fungal species, only 300 have been linked to disease in animals. Fungi are the most common plant pathogens. Human mycoses are caused by true fungal pathogens and opportunistic pathogens. 38

39. Killing Fungi Fungi have given us antibiotics that can treat bacterial infections. There are fewer drugs to treat fungal infections. Why? Fungi are more biologically similar to us.

40. Other Eukaryotes of Microbiological Interest: Parasitic Helminths and Vectors Parasitic worms have microscopic infective and diagnostic stages Arthropod vectors are animals that carry pathogens –Mechanical vectors –Biological vectors Disease vectors belong to two classes of arthropod –Arachnida –Insecta © 2012 Pearson Education Inc.

41. Other Eukaryotes of Microbiological Interest: Parasitic Helminths and Vectors Arachnids –Adult arachnids have four pairs of legs –Ticks are the most important arachnid vectors –Hard ticks are most prominent tick vectors –A few mite species transmit rickettsial diseases © 2012 Pearson Education Inc.

42. Other Eukaryotes of Microbiological Interest: Parasitic Helminths and Vectors Insects –Adult insects have three pairs of legs and three body regions –Include –Fleas –Lice –Flies –Mosquitoes –Kissing bugs © 2012 Pearson Education Inc.

43. Figure 12.33 Representative arthropod vectors-overview