1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 19 Viruses

2. Fig. 19-2 RESULTS 12 3 Extracted sap from tobacco plant with tobacco mosaic disease Passed sap through a porcelain filter known to trap bacteria Rubbed filtered sap on healthy tobacco plants 4 Healthy plants became infected

3. Fig. 19-3 RNA Capsomere of capsid DNA Glycoprotein 18  250 nm 70–90 nm (diameter) Glycoproteins 80–200 nm (diameter) 80  225 nm Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber 50 nm 20 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4

4. Fig. 19-3a (a) Tobacco mosaic virus 20 nm 18  250 nm Capsomere of capsid RNA

5. Fig. 19-3b DNA Capsomere Glycoprotein 70–90 nm (diameter) 50 nm (b) Adenoviruses

6. Fig. 19-3c Membranous envelope RNA Capsid Glycoproteins 80–200 nm (diameter) 50 nm (c) Influenza viruses

7. Fig. 19-3d Head DNA Tail sheath Tail fiber 80  225 nm 50 nm (d) Bacteriophage T4

8. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings General Features of Viral Reproductive Cycles Once a viral genome has entered a cell, the cell begins to manufacture viral proteins The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses Animation: Simplified Viral Reproductive Cycle Animation: Simplified Viral Reproductive Cycle

9. Transcription and manufacture of capsid proteins Self-assembly of new virus particles and their exit from the cell Entry and uncoating Fig. 19-4 VIRUS 1 2 3 DNA Capsid 4 Replication HOST CELL Viral DNA mRNA Capsid proteins Viral DNA

10. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Lytic Cycle The lytic cycle is a phage reproductive cycle that culminates in the death of the host cell The lytic cycle produces new phages and digests the host’s cell wall, releasing the progeny viruses A phage that reproduces only by the lytic cycle is called a virulent phage Bacteria have defenses against phages, including restriction enzymes that recognize and cut up certain phage DNA Animation: Phage T4 Lytic Cycle Animation: Phage T4 Lytic Cycle

11. Fig. 19-5-5 Phage assembly HeadTailTail fibers Assembly Release Synthesis of viral genomes and proteins Entry of phage DNA and degradation of host DNA Attachment 1 2 4 5 3

12. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The Lysogenic Cycle The lysogenic cycle replicates the phage genome without destroying the host The viral DNA molecule is incorporated into the host cell’s chromosome This integrated viral DNA is known as a prophage Every time the host divides, it copies the phage DNA and passes the copies to daughter cells Animation: Phage Lambda Lysogenic and Lytic Cycles Animation: Phage Lambda Lysogenic and Lytic Cycles

13. Fig. 19-6 Phage DNA Phage The phage injects its DNA. Bacterial chromosome Phage DNA circularizes. Daughter cell with prophage Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Cell divisions produce population of bacteria infected with the prophage. The cell lyses, releasing phages. Lytic cycle is induced or Lysogenic cycle is entered Lysogenic cycle Prophage The bacterium reproduces, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages.

14. Table 19-1

15. Fig. 19-7 Capsid RNA Envelope (with glycoproteins) Capsid and viral genome enter the cell HOST CELL Viral genome (RNA) Template mRNA ER Glyco- proteins Capsid proteins Copy of genome (RNA) New virus

16. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings RNA as Viral Genetic Material The broadest variety of RNA genomes is found in viruses that infect animals Retroviruses use reverse transcriptase to copy their RNA genome into DNA HIV (human immunodeficiency virus) is the retrovirus that causes AIDS (acquired immunodeficiency syndrome)

17. Fig. 19-8 Glycoprotein Viral envelope Capsid RNA (two identical strands) Reverse transcriptase HIV Membrane of white blood cell HIV entering a cell 0.25 µm Viral RNA RNA-DNA hybrid HOST CELL Reverse transcriptase DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus New HIV leaving a cell

18. Fig. 19-8a Glycoprotein Reverse transcriptase HIV RNA (two identical strands) Capsid Viral envelope HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus

19. Fig. 19-8b HIV Membrane of white blood cell HIV entering a cell 0.25 µm New HIV leaving a cell

20. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings The viral DNA that is integrated into the host genome is called a provirus Unlike a prophage, a provirus remains a permanent resident of the host cell The host’s RNA polymerase transcribes the proviral DNA into RNA molecules The RNA molecules function both as mRNA for synthesis of viral proteins and as genomes for new virus particles released from the cell Animation: HIV Reproductive Cycle Animation: HIV Reproductive Cycle

21. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mimivirus, a double-stranded DNA virus, is the largest virus yet discovered There is controversy about whether this virus evolved before or after cells

22. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 19.3: Viruses, viroids, and prions are formidable pathogens in animals and plants Diseases caused by viral infections affect humans, agricultural crops, and livestock worldwide Smaller, less complex entities called viroids and prions also cause disease in plants and animals, respectively

23. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Vaccines are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen Vaccines can prevent certain viral illnesses Viral infections cannot be treated by antibiotics Antiviral drugs can help to treat, though not cure, viral infections

24. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Emerging Viruses Emerging viruses are those that appear suddenly or suddenly come to the attention of scientists Severe acute respiratory syndrome (SARS) recently appeared in China Outbreaks of “new” viral diseases in humans are usually caused by existing viruses that expand their host territory

25. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Flu epidemics are caused by new strains of influenza virus to which people have little immunity Viral diseases in a small isolated population can emerge and become global New viral diseases can emerge when viruses spread from animals to humans Viral strains that jump species can exchange genetic information with other viruses to which humans have no immunity

26. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings These strains can cause pandemics, global epidemics The “avian flu” is a virus that recently appeared in humans and originated in wild birds

27. Fig. 19-9 (a) The 1918 flu pandemic (b) Influenza A H5N1 virus (c) Vaccinating ducks 0.5 µm

28. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Viral Diseases in Plants More than 2,000 types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flowers or roots Most plant viruses have an RNA genome

29. Fig. 19-10

30. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Plant viruses spread disease in two major modes: – Horizontal transmission, entering through damaged cell walls – Vertical transmission, inheriting the virus from a parent

31. Fig. 19-11 Prion Normal protein Original prion New prion Aggregates of prions

32. Fig. 19-UN2 Time A B Number of bacteria Number of viruses

33. Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings You should now be able to: 1.Explain how capsids and envelopes are formed 2.Distinguish between the lytic and lysogenic reproductive cycles 3.Explain why viruses are obligate intracellular parasites 4.Describe the reproductive cycle of an HIV retrovirus 5.Describe three processes that lead to the emergence of new diseases 6.Describe viroids and prions