Section 1 Viral Structure and Replication Chapter 24 Objectives • Summarizethe discovery of viruses. • Describewhy viruses are not considered living organisms. • Describethe basic structure of viruses. • Comparethe lytic and lysogenic cycles of virus replication. • Summarizethe origin of viruses.

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, Wendell Stanley demonstrated that viruses were not cells when he crystallized TMV, the virus that causes tobacco mosaic disease in tobacco and tomato plants.

Section 1 Viral Structure and Replication Chapter 24 Virus

Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses • Viruses do not have all of the characteristics of life and are therefore not considered to be living. • Viral Size and Structure • Viruses are nonliving particles containing DNA or RNA and are surrounded by a protein coat called a capsid. • Some viruses also have an envelope that is derived from a host cell’s nuclear membrane or cell membrane.

Section 1 Viral Structure and Replication Chapter 24 Parts of a Virus

Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses, continued • Classification of Viruses • Viruses can be classified based on whether they have • RNA or DNA, • whether the RNA or DNA is single or double stranded and circular or linear, • by capsid shape, • and whether or not they have an envelope.

Section 1 Viral Structure and Replication Chapter 24 Viral Replication • 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 transcribed to RNA along with the host’s DNA.

Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued • Replication in RNA Viruses • The RNA genome of some RNA viruses can be directly translated to make viral proteins. • Retroviruses use reverse transcriptase and RNA as a template to make DNA, which is then used to produce viral RNA and proteins.

Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued • Replication in Viruses That Infect Prokaryotes • Bacteriophagesare viruses that infect bacteria.

Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued • Lytic Cycle • Viruses can follow a lytic cycle, making new viral particles immediately.

Section 1 Viral Structure and Replication Chapter 24 Lytic Cycle

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.

Section 1 Viral Structure and Replication Chapter 24 Lysogenic Cycle

Section 1 Viral Structure and Replication Chapter 24 The Lytic and Lysogenic Cycles

Section 1 Viral Structure and Replication Chapter 24 Viral Replication, continued • Viruses: Tools for Biotechnology • Viruses are important tools for biotechnology.

Section 1 Viral Structure and Replication Chapter 24 The Origin of Viruses • Most scientists think viruses originated from fragments of host-cell nucleic-acid material.

Section 2 Viral Diseases Chapter 24 Objectives • Nameseveral vectors of viral diseases. • Identifyfour viral diseases that result in serious human illnesses. • Discuss the relationship between viruses and cancer. • Namethree examples of emerging viral diseases. • Comparethe effectiveness of vaccination, vector control, and drug therapy in fighting viruses. • Contrastviroids, prions, and viruses.

Section 2 Viral Diseases Chapter 24 Vectors of Viral Diseases • Vectors, or hosts, of viral diseases include humans, animals, and insects.

Section 2 Viral Diseases Chapter 24 Human Viral Diseases • Viruses cause many human diseases, including: • the common cold, • flu, • hepatitis, • rabies, • chickenpox, • certain types of cancer, • and AIDS.

Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued • Chickenpox and Shingles • Chickenpox and shingles are caused by the same varicella-zoster herpesvirus.

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 fecally contaminated food and water. • Hepatitis B, C, and D are spread by sexual contact, by contact with infected blood and serum,and by the use of contaminated needles.

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 macrophages and thus damages the body’s immune system. The disease called acquired immune deficiency syndrome (AIDS) results.

Section 2 Viral Diseases Chapter 24 AIDS (Acquired Immunodeficiency Syndrome)

Section 2 Viral Diseases Chapter 24 Human Viral Diseases, continued • Viruses and Cancer • Some viruses contain oncogenes that can cause cancer, while other viruses convertproto-oncogenes, which usually control cell growth,tooncogenes.

Section 2 Viral Diseases Chapter 24 Emerging Viral Diseases • Emerging viruses usually infect animals isolated in nature but can jump to humans when contact occurs in the environment.

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 an immune response when introduced to the body. • Vaccines have helped to greatly reduce certain viral diseases.

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.

Section 2 Viral Diseases Chapter 24 Prevention and Treatment, continued • Drug Therapy • Antibiotics are ineffective against viral diseases. • Viral drugs, such as acyclovir, block specific steps in viral replication.

Section 2 Viral Diseases Chapter 24 Virods and Prions • Viroids are short, circular, single strands of RNA lacking a capsid that infect plant cells. • Prionsare infectious particles containing protein but no nucleic acids. • Prions cause mad cow disease and similar degenerative brain diseases.

Section 2 Viral Diseases Chapter 24 Important Viral Diseases

Chapter 24 Standardized Test Prep Multiple Choice 1. What are viruses made of? A. enzymes and fats B. carbohydrates and ATP C. protein and nucleic acids D. mitochondria and lysosomes

Chapter 24 Standardized Test Prep Multiple Choice, continued 1. What are viruses made of? A. enzymes and fats B. carbohydrates and ATP C. protein and nucleic acids D. mitochondria and lysosomes

Chapter 24 Standardized Test Prep Multiple Choice, continued 2. How do viroids differ from viruses? F. Viroids are larger in size. G. Viroids do not have a capsid. H. Viroids do not have nucleic acids. J. Viroids can cause disease in plants.

Chapter 24 Standardized Test Prep Multiple Choice, continued 3. During which of the following processes does a phage kill its host? A. conjugation B. transcription C. the lytic cycle D. the lysogenic cycle

Chapter 24 Standardized Test Prep Multiple Choice, continued 4. Which of the following is one reason why viruses are not considered living organisms? F. Viruses are able to grow. G. Viruses do not metabolize. H. Viruses can reproduce by splitting. J. Viruses are too small to be easily observed.

Use the figure below to answer questions 5 - 6. 5. Which of the following does the diagram represent? A. a virus B. a prion C. a viroid D. a bacterium Chapter 24 Standardized Test Prep Multiple Choice,continued

5. Which of the following does the diagram represent? A. a virus B. a prion C. a viroid D. a bacterium Use the figure below to answer questions 5 - 6. Chapter 24 Standardized Test Prep Multiple Choice,continued

6. To which of the following is label X pointing? F. envelope G. nucleic acid H. protein coat J. cell membrane Use the figure below to answer questions 5 - 6. Chapter 24 Standardized Test Prep Multiple Choice,continued

Chapter 24 Standardized Test Prep Multiple Choice, continued Complete the following analogy: 7. skin : person :: capsid : A. virus B. insect C. fungus D. bacterium

Use the figure below to answer question 8. The figure below represents the human immunodeficiency virus. 8. The structure labeled Y represents which of the following? F. capsid G. envelope H. RNA genome J. reverse transcriptase Chapter 24 Standardized Test Prep Multiple Choice,continued

8. The structure labeled Y represents which of the following? F. capsid G. envelope H. RNA genome J. reverse transcriptase Use the figure below to answer question 8. The figure below represents the human immunodeficiency virus. Chapter 24 Standardized Test Prep Multiple Choice,continued

Chapter 24 Standardized Test Prep Short Response Reverse transcriptase is an enzyme that catalyzes the synthesis of DNA from RNA. Explain why RNA viruses must have reverse transcriptase to replicate.

Chapter 24 Standardized Test Prep Short Response, continued Reverse transcriptase is an enzyme that catalyzes the synthesis of DNA from RNA. Explain why RNA viruses must have reverse transcriptase to replicate. Answer: Retroviruses need reverse transcriptase to make DNA that can be inserted into the host cell’s genome for replication.

Chapter 24 Standardized Test Prep Extended Response Base your answers to parts A & B on the information below. Viruses share several characteristics of living organisms. However, viruses are not considered to be living. Part A Compare the characteristics viruses share with living organisms to the characteristics they do not share with living organisms. Part B Would you anticipate more or fewer emerging viral diseases to appear in the future? Explain.

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