1. End Show Slide 1 of 34 Copyright Pearson Prentice Hall Biology

2. End Show Slide 2 of 34 Copyright Pearson Prentice Hall 19–2 Viruses

3. End Show 19–2 Viruses Slide 3 of 34 Copyright Pearson Prentice Hall What Is a Virus? Viruses are particles of nucleic acid, protein, and in some cases, lipids. Viruses can reproduce only by infecting living cells.

4. End Show 19–2 Viruses Slide 4 of 34 Copyright Pearson Prentice Hall What Is a Virus? Head Tail sheath DNA T4 Bacteriophage Tobacco Mosaic Virus Influenza Virus RNA Membrane envelope Tail fiber RNA Capsid proteins Capsid Surface proteins

5. End Show 19–2 Viruses Slide 5 of 34 Copyright Pearson Prentice Hall What Is a Virus? A typical virus is composed of a core of DNA or RNA surrounded by a protein coat. A capsid is the virus’s protein coat.

6. End Show 19–2 Viruses Slide 6 of 34 Copyright Pearson Prentice Hall Viral Infection Once the virus is inside the host cell, two different processes may occur. Some viruses replicate immediately, killing the host cell. Others replicate, but do not kill the host cell immediately.

7. End Show 19-2 Viruses Slide 7 of 34 Copyright Pearson Prentice Hall Viral Infection Bacteriophage injects DNA into bacterium Bacteriophage DNA forms a circle Lytic Infection Lysogenic Infection

8. End Show 19–2 Viruses Slide 8 of 34 Copyright Pearson Prentice Hall Viral Infection Lytic Infection In a lytic infection, a virus enters a cell, makes copies of itself, and causes the cell to burst.

9. End Show 19–2 Viruses Slide 9 of 34 Copyright Pearson Prentice Hall Viral Infection

10. End Show 19–2 Viruses Slide 10 of 34 Copyright Pearson Prentice Hall Viral Infection

11. End Show 19–2 Viruses Slide 11 of 34 Copyright Pearson Prentice Hall Viral Infection

12. End Show 19–2 Viruses Slide 12 of 34 Copyright Pearson Prentice Hall Viral Infection Lysogenic Infection Other viruses cause lysogenic infections in which a host cell makes copies of the virus indefinitely. In a lysogenic infection, a virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell's DNA.

13. End Show 19–2 Viruses Slide 13 of 34 Copyright Pearson Prentice Hall Viral Infection

14. End Show 19–2 Viruses Slide 14 of 34 Copyright Pearson Prentice Hall Viral Infection

15. End Show 19–2 Viruses Slide 15 of 34 Copyright Pearson Prentice Hall Viral Infection

16. End Show 19–2 Viruses Slide 16 of 34 Copyright Pearson Prentice Hall Viral Infection

17. End Show 19–2 Viruses Slide 17 of 34 Copyright Pearson Prentice Hall

18. End Show 19–2 Viruses Slide 18 of 34 Copyright Pearson Prentice Hall Retroviruses Retroviruses contain RNA as their genetic information. When retroviruses infect cells, they make a DNA copy of their RNA. This DNA is inserted into the DNA of the host cell.

19. End Show - or - Continue to: Click to Launch: Slide 19 of 34 Copyright Pearson Prentice Hall 19–2

20. End Show Slide 20 of 34 Copyright Pearson Prentice Hall 19–2 Viruses that contain RNA as their genetic information are known as a.prions. b.oncoviruses. c.retroviruses. d.bacteriophage.

21. End Show Slide 21 of 34 Copyright Pearson Prentice Hall 19–2 The first type of virus to be studied was the a.bacteriophage. b.tobacco mosaic virus. c.influenza virus. d.AIDS virus.

22. End Show Slide 22 of 34 Copyright Pearson Prentice Hall 19–2 Which of the following statements about viruses is true? a.Viruses appear similar to bacteria when studied with a light microscope. b.Viruses display the essential characteristics of living things. c.Viruses can reproduce independently if they contain DNA. d.Viruses cannot reproduce unless they infect a living cell.

23. End Show Slide 23 of 34 Copyright Pearson Prentice Hall 19–2 A virus integrates its DNA into the DNA of the host cell but remains inactive for a while in a.a lytic infection. b.a lysogenic infection. c.neither a lytic nor a lysogenic infection. d.retroviral infection.

24. End Show Slide 24 of 34 Copyright Pearson Prentice Hall 19–2 Retroviruses are considered unique because a.they have RNA in their capsid and not DNA. b.they have DNA in their capsid and not RNA. c.after infection of a host cell, their RNA makes DNA. d.after infection of a host cell, their DNA makes RNA.

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