1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Viruses Chapter 19

2. Overview: A Borrowed Life Viruses called __________________can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli Viruses lead “a kind of _______________” between life-forms and chemicals The origins of _______________ biology lie in early studies of viruses that infect bacteria © 2011 Pearson Education, Inc.

3. Concept 19.1: A virus consists of a nucleic acid surrounded by a protein coat Viruses were detected ______________ long before they were actually seen © 2011 Pearson Education, Inc.

4. The Discovery of Viruses: Scientific Inquiry ___________________ disease stunts growth of tobacco plants and gives their leaves a mosaic coloration In the late 1800s, researchers hypothesized that a particle ______________ than bacteria caused the disease In 1935, Wendell Stanley confirmed this hypothesis by crystallizing the infectious particle, now known as _______________________(TMV) © 2011 Pearson Education, Inc.

5. Figure 19.2 Extracted sap from tobacco plant with tobacco mosaic disease RESULTS Passed sap through a porcelain filter known to trap bacteria Healthy plants became infected Rubbed filtered sap on healthy tobacco plants 1234

6. Structure of Viruses Viruses __________ cells A ____________ is a very small infectious particle consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope © 2011 Pearson Education, Inc.

7. Viral Genomes Viral genomes may consist of either –Double- or single-stranded ________, or –Double- or single-stranded ________ Depending on its type of nucleic acid, a virus is called a _________ virus or an __________ virus © 2011 Pearson Education, Inc.

8. Capsids and Envelopes A __________ is the protein shell that encloses the viral genome Capsids are built from protein subunits called __________________ A capsid can have various structures © 2011 Pearson Education, Inc.

9. Figure 19.3 Capsomere of capsid RNA Capsomere DNA Glycoprotein Glycoproteins Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber 18  250 nm 80  225 nm 70–90 nm (diameter) 80–200 nm (diameter) 20 nm 50 nm (a) Tobacco mosaic virus (b) Adenoviruses (c) Influenza viruses(d) Bacteriophage T4

10. Some viruses have _____________________ that help them infect hosts These _________________surround the capsids of ______________ viruses and many other viruses found in animals Viral envelopes, which are derived from the host cell’s membrane, contain a combination of _____ and ____________________ © 2011 Pearson Education, Inc.

11. ______________, also called __________, are viruses that infect bacteria They have the most ___________________ found among viruses Phages have an ___________________ that encloses their DNA A _______________ piece attaches the phage to the host and injects the phage DNA inside © 2011 Pearson Education, Inc.

12. Concept 19.2: Viruses replicate only in host cells Viruses are ________________________, which means they can replicate only within a host cell Each virus has a ________________, a limited number of host cells that it can infect © 2011 Pearson Education, Inc.

13. General Features of Viral Replicative Cycles Once a viral genome has entered a cell, the cell begins to manufacture ________________ The virus makes use of host ________________ ___________________________, and other molecules Viral nucleic acid molecules and capsomeres spontaneously ________________ into new viruses © 2011 Pearson Education, Inc.

14. VIRUS 2134 Entry and uncoating Replication Transcription and manufacture of capsid proteins Self-assembly of new virus particles and their exit from the cell DNA Capsid HOST CELL Viral DNA mRNA Capsid proteins Figure 19.4

15. Replicative Cycles of Phages __________ are the best understood of all viruses Phages have two reproductive mechanisms: the _______ cycle and the _________________cycle © 2011 Pearson Education, Inc.

16. The Lytic Cycle The _______________ is a phage replicative cycle that culminates in the death of the host cell The lytic cycle produces new phages and ______ (breaks open) the host’s cell wall, releasing the progeny viruses A phage that reproduces only by the lytic cycle is called a _____________________ Bacteria have defenses against phages, including ______________________ that recognize and cut up certain phage DNA © 2011 Pearson Education, Inc.

17. Figure 19.5-5 Attachment 21543 Entry of phage DNA and degradation of host DNA Release Synthesis of viral genomes and proteins Assembly Phage assembly Head TailTail fibers

18. The Lysogenic Cycle The ____________________ replicates the phage genome without destroying the host The viral DNA molecule is _______________ into the ____________________________ This integrated viral DNA is known as a ________ Every time the host divides, it ________________ _________ and passes the copies to daughter cells © 2011 Pearson Education, Inc.

19. An ____________________can trigger the virus genome to exit the bacterial chromosome and switch to the lytic mode Phages that use both the lytic and lysogenic cycles are called _______________________ © 2011 Pearson Education, Inc.

20. Figure 19.6 New phage DNA and proteins are synthesized and assembled into phages. The cell lyses, releasing phages. Phage Phage DNA The phage injects its DNA. Bacterial chromosome Lytic cycle lytic cycle is induced or Phage DNA circularizes. Certain factors determine whether lysogenic cycle is entered Lysogenic cycle Prophage Daughter cell with prophage Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Cell divisions produce a population of bacteria infected with the prophage. The bacterium reproduces, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage.

21. New phage DNA and proteins are synthesized and assembled into phages. The cell lyses, releasing phages. Phage Phage DNA The phage injects its DNA. Bacterial chromosome Lytic cycle lytic cycle is induced or Phage DNA circularizes. Certain factors determine whether lysogenic cycle is entered Figure 19.6a

22. lytic cycle is induced or Phage DNA circularizes. Certain factors determine whether lysogenic cycle is entered Lysogenic cycle Prophage Daughter cell with prophage Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Cell divisions produce a population of bacteria infected with the prophage. The bacterium reproduces, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. Figure 19.6b

23. Replicative Cycles of Animal Viruses There are two key variables used to classify viruses that infect animals –___________? –_______________________________________? © 2011 Pearson Education, Inc.

24. Table 19.1a

25. Table 19.1b

26. Viral Envelopes Many viruses that infect animals have a _________________________ _________________________ on the envelope bind to specific receptor molecules on the surface of a host cell Some viral envelopes are formed from the host cell’s plasma membrane as the _______________ © 2011 Pearson Education, Inc.

27. Other viral membranes form from the ________ ______________________ and are then replaced by an envelope made from Golgi apparatus membrane © 2011 Pearson Education, Inc.

28. Figure 19.7 Capsid RNA Envelope (with glycoproteins) Capsid and viral genome enter the cell HOST CELL Viral genome (RNA) Template mRNA ER Capsid proteins Copy of genome (RNA) New virus Glyco- proteins

29. RNA as Viral Genetic Material The broadest variety of RNA genomes is found in viruses that infect _____________ _______________ use __________________ to copy their RNA genome into DNA _______________________________ is the retrovirus that causes __________ (acquired immunodeficiency syndrome) © 2011 Pearson Education, Inc.

30. Glycoprotein Reverse transcriptase HIV Viral envelope Capsid RNA (two identical strands) HOST CELL Viral RNA Reverse transcriptase RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation mRNA New virus HIV Membrane of white blood cell 0.25  m HIV entering a cell New HIV leaving a cell Figure 19.8

31. The viral DNA that is integrated into the host genome is called a ________________ Unlike a prophage, a provirus remains a _________________________of the host cell The ______________________ transcribes the proviral DNA into ___________________ The RNA molecules function both as mRNA for synthesis of __________________ and as _______________________ released from the cell © 2011 Pearson Education, Inc.

32. Evolution of Viruses Viruses ____________our definition of living organisms Since viruses can replicate only within cells, they probably evolved as ______________________ Candidates for the source of viral genomes are ______________, circular DNA in bacteria and yeasts, and ________________, small mobile DNA segments Plasmids, transposons, and viruses are all _____ _______________________________ © 2011 Pearson Education, Inc.

33. ______________, a double-stranded DNA virus, the largest virus yet discovered, is the size of a small bacterium There is controversy about whether this virus evolved before or after cells © 2011 Pearson Education, Inc.

34. 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 __________ and ___________ also cause disease in plants and animals, respectively © 2011 Pearson Education, Inc.

35. Viral Diseases in Animals Viruses may damage or kill cells by causing the release of ___________________ from lysosomes Some viruses cause infected cells to produce __________ that lead to disease symptoms Others have molecular components such as ______________________ that are toxic © 2011 Pearson Education, Inc.

36. _______________ are harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen Vaccines can prevent certain _________ illnesses Viral infections cannot be treated by __________ ___________________ can help to treat, though not cure, viral infections © 2011 Pearson Education, Inc.

37. Emerging Viruses ____________________ are those that suddenly become apparent Recently, a general outbreak (___________) of a flu-like illness appeared in Mexico and the United States, caused by an influenza virus named _____ ____________________ are caused by new strains of influenza virus to which people have little immunity © 2011 Pearson Education, Inc.

38. These strains can cause _____________, global epidemics The 2009 flu pandemic was likely passed to humans from ______; for this reason it was originally called the “______________” © 2011 Pearson Education, Inc.

39. Viral diseases in a small isolated population can emerge and become ___________ New viral diseases can emerge when viruses spread from ____________________ Viral strains that _____________ can exchange genetic information with other viruses to which humans have no immunity © 2011 Pearson Education, Inc.

40. Figure 19.9 (c) 1918 flu pandemic 2009 pandemic screening (b) 2009 pandemic H1N1 influenza A virus (a) 1  m

41. Viral Diseases in Plants More than 2,000 types of viral diseases of ______ are known and cause spots on leaves and fruits, stunted growth, and damaged flowers or roots Most plant viruses have an ___________ genome © 2011 Pearson Education, Inc.

42. Figure 19.10

43. Plant viruses spread disease in two major modes –____________________, entering through damaged cell walls –____________________, inheriting the virus from a parent © 2011 Pearson Education, Inc.

44. Viroids and Prions: The Simplest Infectious Agents __________ are small circular RNA molecules that infect plants and disrupt their growth __________are slow-acting, virtually indestructible infectious proteins that cause brain diseases in mammals Prions propagate by _____________________ into the prion version Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions © 2011 Pearson Education, Inc.

45. Figure 19.11 Prion Normal protein Original prion New prion Aggregates of prions