Table of Contents Section 1 Viral Structure and Replication Viruses Chapter 24 Table of Contents Section 1 Viral Structure and Replication Section 2 Viral Diseases

Objectives Chapter 24 Summarize the discovery of viruses. 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.

What is happening in the photograph? Newly assembled HIV viruses are leaving the T cell. How did the viruses, pictured leaving the cell, enter the cell? The genetic material from a single HIV particle entered the cell and was responsible for the production of all the viruses pictured.

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. Virus

Characteristics of Viruses Section 1 Viral Structure and Replication Chapter 24 Characteristics of Viruses What are the characteristics of living organisms? Cellular organization, reproduction, metabolism, homeostasis, heredity, responsiveness, and growth and development. Viruses do not have all of the characteristics of life and are therefore not considered to be living.

Characteristics of Viruses, continued 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 capsid. Some viruses also have an envelope that is derived from a host cell’s nuclear membrane or cell membrane. Parts of a Virus

Characteristics of Viruses, continued 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.

Review What have we learned about the size and structure of viruses? Very small Various sizes and shapes (helical, polyhedral, enveloped) How are viruses classified? RNA or DNA Single or double stranded Linear or circular Capsid characteristics Presence or absence of envelope

Viral Replication, continued 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 transcribed to RNA along with the host’s DNA.

Viral Replication, continued 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. HIV, murine leukemia virus, feline immunodeficiency virus.

Reverse Transcriptase Why is the enzyme contained in retroviruses called reverse transcriptase? Catalyzes the transcription of DNA from RNA

Viral Replication Replication in Viruses That Infect Prokaryotes Section 1 Viral Structure and Replication Chapter 24 Viral Replication Replication in Viruses That Infect Prokaryotes Bacteriophages are viruses that infect bacteria.

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

Viral Replication, continued 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. Not active

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

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

Review How do viruses reproduce? Directly produce RNA Insert into host DNA Lytic or lysogenic cycles

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.

Objectives Chapter 24 Section 2 Viral Diseases 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.

Vectors of Viral Diseases 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.

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

Human Viral Diseases, continued 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.

Human Viral Diseases, continued 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.

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

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

Emerging Viral Diseases 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.

Prevention and Treatment 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.

Prevention and Treatment, continued 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.

Prevention and Treatment, continued 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. Prions are infectious particles containing protein but no nucleic acids. Prions cause mad cow disease and similar degenerative brain diseases.

Important Viral Diseases Section 2 Viral Diseases Chapter 24 Important Viral Diseases