2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Viruses Chapter 24 Table of Contents Section 1 Viral Structure and Replication Section 2 Viral Diseases

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Objectives Summarize the discovery of viruses. Describe why viruses are not considered living organisms. Describe the basic structure of viruses. Compare the lytic and lysogenic cycles of virus replication. Summarize the origin of viruses.

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Discovery of Viruses Researchers in the late 1800s discovered that something smaller than bacteria could cause disease. In 1935, ________________ ______________ demonstrated that viruses were not cells when he crystallized _______, the virus that causes tobacco mosaic disease in tobacco and tomato plants.

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses Viruses do not have all of the characteristics of life and are therefore

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses, continued Viral Size and Structure –Viruses are nonliving particles containing DNA or RNA and are surrounded by a protein coat called a ______________________. –Some viruses also have an _______________ that is derived from a host cell’s nuclear membrane or cell membrane.

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses, continued Classification of Viruses –Viruses can be classified based on whether they have __________ or _________, whether the RNA or DNA is _____________ or ____________ stranded and ______________ or ____________, by ____________ ______________, and whether or not they have an ___________________.

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Replication in DNA Viruses –DNA viruses can enter host cells and directly produce RNA, or they can insert into a host’s chromosome, where they are

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Replication in RNA Viruses –The RNA genome of some RNA viruses can be –____________________ use ____________ ___________________ and RNA as a template to make DNA, which is then used to produce viral RNA and proteins.

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Replication in Viruses That Infect Prokaryotes –Bacteriophages are

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Lytic Cycle –Viruses can follow a lytic cycle, making new viral particles immediately.

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Lysogenic Cycle –Viruses can follow a lysogenic cycle, becoming part of the host genome and making new particles later.

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 24 The Lytic and Lysogenic Cycles Section 1 Viral Structure and Replication

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued Viruses: Tools for Biotechnology –Viruses are important tools for biotechnology.

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Viral Structure and Replication Chapter 24 The Origin of Viruses Most scientists think viruses originated from

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Objectives Name several vectors of viral diseases. Identify four viral diseases that result in serious human illnesses. Discuss the relationship between viruses and cancer. Name three examples of emerging viral diseases. Compare the effectiveness of vaccination, vector control, and drug therapy in fighting viruses. Contrast viroids, prions, and viruses.

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Vectors of Viral Diseases Vectors, or hosts, of viral diseases include

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Human Viral Diseases Viruses cause many human diseases, including the

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued Chickenpox and Shingles –Chickenpox and shingles are caused by the same varicella-zoster herpesvirus.

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued Viral Hepatitis –Hepatitis, or inflammation of the liver, can be caused by at least five viruses. –Hepatitis A and hepatitis E can be spread by –Hepatitis B, C, and D are spread by

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued Acquired Immune Deficiency Syndrome (AIDS) –The human immunodeficiency virus (HIV) is an RNA virus spread by sexual contact, by contact with infected body fluids, and from mother to fetus. –HIV targets _____________________ and thus damages the body’s immune system. The disease called acquired immune deficiency syndrome (AIDS) results.

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 24 AIDS (Acquired Immunodeficiency Syndrome) Section 2 Viral Diseases

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued Viruses and Cancer –Some viruses contain _________________ that can cause cancer, while other viruses convert ___________________________, which usually control cell growth, to oncogenes.

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Emerging Viral Diseases Emerging viruses usually infect animals isolated in nature but can jump to humans when

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Prevention and Treatment Vaccinations –A vaccine contains a harmless version of a virus, bacterium, or a toxin that causes –Vaccines have helped to greatly reduce certain viral diseases.

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Prevention and Treatment, continued Vector Control –Control efforts, including killing mosquitoes and other vectors and quarantining ill patients, have helped reduce the spread of certain viral diseases.

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Prevention and Treatment, continued Drug Therapy –_____________________ are ineffective against viral diseases. –Viral drugs, such as acyclovir, block

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 Viral Diseases Chapter 24 Virods and Prions ____________________ are short, circular, single strands of RNA lacking a capsid that infect plant cells. _____________________ are infectious particles containing protein but no nucleic acids. –Prions cause mad cow disease and similar degenerative brain diseases.

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 24 Important Viral Diseases Section 2 Viral Diseases