1. Albia Dugger Miami Dade College Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 19 Viruses, Bacteria, and Archaeans (Sections 19.1 - 19.5)

2. 19.1 Evolution of a Disease Scientists use knowledge of evolution to investigate how a new disease such as AIDS can arise and spread in the human population By sequencing the HIV-1 genome and comparing it to genomes of primate viruses, researchers found that the human virus evolved from simian immunodeficiency virus (SIV), which infects wild chimpanzees

3. HIV Infection New HIV particle budding from an infected white blood cell

4. 19.2 Viral Structure and Function A virus is a noncellular infectious agent that consists of a protein coat around a core of DNA or RNA In some viruses, the coat is enveloped in a bit of plasma membrane derived from a previous host virus Noncellular, infectious particle of protein and nucleic acid; replicates only in a host cell

5. Viral Traits and Diversity A virus is far smaller than any cell and has no ribosomes or other metabolic machinery Each type of virus has structural adaptations that allow it to infect and replicate in hosts of a particular type A bacteriophage is a virus that infects bacteria

6. Examples of Viral Structure T4 bacteriophage has a complex coat DNA is encased in a protein “head” Fibers on rodlike “tail” attach virus to host

7. Fig. 19.2a, p. 298 A T4 bacteriophage DNA inside protein coat tail fiber sheath Examples of Viral Structure

8. Tobacco mosaic virus has a helical structure, with coat proteins arranged around RNA to form a rod

9. Fig. 19.2b, p. 298 B Tobacco mosaic virus protein subunits of coat RNA Examples of Viral Structure

10. Many animal viruses have a 20-sided protein coat Adenoviruses are “naked,” but the coat has a protein spike at each corner

11. Fig. 19.2c, p. 298 C Adenovirus 20-sided protein coat that encloses DNA Examples of Viral Structure

12. Most animal viruses are enveloped; membrane from a prior host encloses the virus Herpesviruses are enveloped DNA viruses HIV is an enveloped RNA virus

13. Fig. 19.2d, p. 298 D Herpesvirus lipid envelope with protein components 20-sided protein coat beneath the envelope viral DNA and enzymes Examples of Viral Structure

14. Viral Replication Because a virus lacks ribosomes and other metabolic machinery, it must replicate inside a host cell Viruses attach to a host cell, then enter it or insert viral genetic material into it Viral genes and enzymes direct the host to replicate viral genetic material and make viral proteins New viral particles self-assemble and are released

15. Bacteriophage Replication Bacteriophages have two types of replication pathways: In a lytic pathway, multiplication is rapid, and new viral particles are released by lysis In a lysogenic pathway, the virus enters a latent state that extends the cycle

16. Key Terms lysogenic pathway Bacteriophage replication path in which viral DNA becomes integrated into the host’s chromosome and is passed to the host’s descendants lytic pathway Bacteriophage replication pathway in which a virus immediately replicates in its host and kills it

17. Bacteriophage Replication Pathways

18. Fig. 19.3, p. 299 A4 Viral enzyme excises viral DNA from chromosome. C Viral proteins self- assemble into a coat around viral DNA. D Accessory parts are attached to viral coat. B Host replicates viral genetic material, builds viral proteins. A3 Cell divides; recombinant DNA in each descendant cell. A2 Chromosome and integrated viral DNA are replicated. Lysogenic Pathway Lytic Pathway A1 Viral DNA is inserted into host chromosome by viral enzyme action. A Viral particle binds, injects genetic material. E Lysis of host cell lets new viral particles escape. Bacteriophage Replication Pathways

19. A2 Chromosome and integrated viral DNA are replicated. E Lysis of host cell lets new virus particles escape. A Virus particle binds, injects genetic material. Lytic Pathway A1 Viral DNA is inserted into host chromosome by viral enzyme action. Lysogenic Pathway D Accessory parts are attached to viral coat. B Host replicates viral genetic material, builds viral proteins. A3 Cell divides; recombinant DNA in each descendant cell. C Viral proteins self- assemble into a coat around viral DNA. A4 Viral enzyme excises viral DNA from chromosome. Fig. 19.3, p. 299 Stepped Art Bacteriophage Replication Pathways

20. ANIMATION: Bacteriophage multiplication cycles To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

21. HIV Replication HIV is an enveloped RNA virus that replicates in human white blood cells Viral RNA in the cell must be reverse transcribed to DNA to begin replication The virus acquires its envelope as it buds from the cell membrane

22. 9 Steps in HIV Replication 1. Virus binds to a host cell 2. Viral RNA and enzymes enter cell 3. Viral reverse transcriptase uses viral RNA to make double- stranded viral DNA 4. Viral DNA integrates into host genome 5. Transcription produces viral RNA 6. Some viral RNA is translated to produce viral proteins 7. Other viral RNA forms the new viral genome 8. Viral proteins and RNA self-assemble at the host membrane 9. New virus buds with an envelope of host membrane

23. Replication Cycle of HIV

24. Fig. 19.4, p. 299 New virus buds from the host cell, with an envelope of host plasma membrane. HIV HIV RNA Virus binds to a host cell. Viral RNA and enzymes enter cell. Viral reverse transcriptase uses viral RNA to make double-stranded viral DNA. Viral DNA integrates into host genome. Transcription produces viral RNA. Some viral RNA is translated to produce viral proteins. Other viral RNA forms the new viral genome. Viral proteins and viral RNA self- assemble at the host membrane. translation reverse transcription transcription HIV DNA 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 9 Replication Cycle of HIV

25. Fig. 19.4, p. 299 HIV 1 Stepped Art HIV RNA 2 reverse transcription HIV DNA 3 4 transcription 5 translation 6 7 8 9 Replication Cycle of HIV

26. ANIMATION: HIV replication cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

27. ANIMATION: Body plans of viruses To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

28. ANIMATION: Lytic Pathway To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

29. ANIMATION: Lysogenic Pathway To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

30. 19.3 Viral Effects on Human Health Some viruses have a positive effect on human health, as when bacteriophages kill bacteria that could cause food poisoning – however, other viruses are pathogens pathogen Disease-causing agent

31. Common Viral Diseases Nonenveloped viruses: Adenoviruses (colds) Viral gastroenteritis (stomach flu) Human papillomavirus (genital warts, cervical cancer) Enveloped viruses: Herpesviruses (cold sores, genital herpes, infectious mononucleosis, chicken pox) Influenza (flu) Mumps, measles, and German measles

32. Emerging Viral Diseases Changes to viral genomes as a result of mutation or gene exchanges can alter the properties of a viral disease emerging disease A disease that was previously unknown, is new to humans, or has recently begun spreading to a new region

33. West Nile Fever West Nile virus is an enveloped RNA virus that replicates in birds; mosquitoes carry the virus from host to host (the vector for this virus) In about 1 percent of cases, West Nile fever attacks the nervous system and can be fatal West Nile fever is an endemic disease throughout the continental United States (present, but at a low level)

34. Key Terms vector Animal that carries a pathogen from one host to the next endemic disease Disease that persists at a low level in a region or population

35. SARS Sudden acute respiratory syndrome (SARS) first appeared in late 2002 in China – it quickly became an epidemic, then a pandemic, killing 774 people in 37 countries in 9 months epidemic Disease outbreak limited to one region pandemic Outbreak of disease that affects many separate regions and poses a serious threat to human health

36. SARS Coronavirus A previously unknown type of coronavirus (right) causes SARS A similar virus in Chinese horseshoe bats probably evolved in other animals before infecting humans

37. The SARS Epidemic A health care worker puts on protective gear during the SARS epidemic

38. Influenza H5N1 and H1N1 Influenzaviruses commonly cause seasonal flu outbreaks Avian influenza H5N1 (bird flu) occasionally infects people who are in contact with birds, and has a high mortality rate Influenza H1N1 (swine flu) first appeared in 2009, can cause severe respiratory symptoms, and is easily transmitted

39. 19.4 Viroids: Tiny Plant Pathogens A new type of pathogen, a small RNA without a protein coat, was discovered in 1971 Viroids do not encode proteins, but are ribozymes (RNAs with enzymatic activity) All known viroids are circular, single-stranded RNAs Remarkably small, viroids have fewer than 400 nucleotides viroid Small noncoding RNA that can infect plants

40. Key Concepts Viruses and Viroids Viruses are noncellular, with a protein coat and a genome of nucleic acid, but no metabolic machinery Viruses must infect cells to replicate Some infect humans and cause disease Viroids are RNA bits that do not encode proteins Even so, they can infect plant cells and replicate inside them

41. 19.5 Bacterial Structure and Function Bacteria are small, structurally simple cells Biologists describe bacteria by their shapes Coccus (spherical) Bacillus (rod-shaped) Spirillum (spiral)

42. Fig. 19.6a, p. 302 spirillum coccus bacillus A 19.5 Bacterial Structure and Function

43. Cell Size, Structure, and Motility Bacteria do not have a nucleus or cytoplasmic organelles typical of eukaryotes A single bacterial chromosome, a circle of double-stranded DNA, resides in a cytoplasmic region called the nucleoid Surface structures include a cell wall, a protective capsule or slime layer, one or more flagella, and hairlike extensions (pili)

44. Key Terms bacterial chromosome Circle of double-stranded DNA that resides in the bacterial cytoplasm nucleoid Cytoplasmic region where prokaryotic chromosome lies pilus Hairlike extension from the cell wall of some bacteria

45. Bacterial Body Plan

46. Fig. 19.6b, p. 302 plasma membrane cytoplasm, with ribosomes cell wall DNA, in nucleoid bacterial flagellum pilus outer capsule B Bacterial Body Plan

47. ANIMATION: Prokaryotic fission To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

48. Abundance and Metabolic Diversity 5 million trillion trillion bacterial cells live on Earth As a group, bacteria are metabolically diverse, including all four known modes of nutrition: Photoautotrophs Chemoautotrophs Photoheterotrophs Chemoheterotrophs

49. 4 Nutritional Modes Mode of Nutrition Energy Source Carbon Source Photoautotrophic Sunlight Carbon dioxide Chemoautotrophic Inorganic substances Carbon dioxide Photoheterotrophic Sunlight Organic compounds Chemoheterotrophic Organic compounds Organic compounds

50. Key Concepts Structure and Function of Bacteria Bacteria are small cells with DNA and ribosomes, but no nucleus or typical eukaryotic organelles They are the most abundant and metabolically diverse organisms, with autotrophs (self-feeders) and heterotrophs (feeders on others) among them