Presentation on theme: "Table of Contents Section 1 Viral Structure and Replication"— Presentation transcript:
1Table of Contents Section 1 Viral Structure and Replication VirusesChapter 24Table of ContentsSection 1 Viral Structure and ReplicationSection 2 Viral Diseases
2Objectives Chapter 24 Summarize the discovery of viruses. Section 1 Viral Structure and ReplicationChapter 24ObjectivesSummarize 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.
3What 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.
4Section 1 Viral Structure and Replication Chapter 24Discovery of VirusesResearchers 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
5Characteristics of Viruses Section 1 Viral Structure and ReplicationChapter 24Characteristics of VirusesWhat 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.
6Characteristics of Viruses, continued Section 1 Viral Structure and ReplicationChapter 24Characteristics of Viruses, continuedViral Size and StructureViruses 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
8Characteristics of Viruses, continued Section 1 Viral Structure and ReplicationChapter 24Characteristics of Viruses, continuedClassification of VirusesViruses 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.
9Review What have we learned about the size and structure of viruses? Very smallVarious sizes and shapes (helical, polyhedral, enveloped)How are viruses classified?RNA or DNASingle or double strandedLinear or circularCapsid characteristicsPresence or absence of envelope
10Viral Replication, continued Section 1 Viral Structure and ReplicationChapter 24Viral Replication, continuedReplication in DNA VirusesDNA 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.
11Viral Replication, continued Section 1 Viral Structure and ReplicationChapter 24Viral Replication, continuedReplication in RNA VirusesThe 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.
12Reverse Transcriptase Why is the enzyme contained in retroviruses called reverse transcriptase?Catalyzes the transcription of DNA from RNA
13Viral Replication Replication in Viruses That Infect Prokaryotes Section 1 Viral Structure and ReplicationChapter 24Viral ReplicationReplication in Viruses That Infect ProkaryotesBacteriophages are viruses that infect bacteria.
14Viral Replication, continued Section 1 Viral Structure and ReplicationChapter 24Viral Replication, continuedLytic CycleViruses can follow a lytic cycle, making new viral particles immediately.Occurs when virus is active
15Viral Replication, continued Section 1 Viral Structure and ReplicationChapter 24Viral Replication, continuedLysogenic CycleViruses can follow a lysogenic cycle, becoming part of the host genome and making new particles later.Not active
16The Lytic and Lysogenic Cycles Section 1 Viral Structure and ReplicationChapter 24The Lytic and Lysogenic Cycles
17Viral Replication, continued Section 1 Viral Structure and ReplicationChapter 24Viral Replication, continuedViruses: Tools for BiotechnologyViruses are important tools for biotechnology.
18Review How do viruses reproduce? Directly produce RNA Insert into host DNALytic or lysogenic cycles
19Section 1 Viral Structure and Replication Chapter 24The Origin of VirusesMost scientists think viruses originated from fragments of host-cell nucleic-acid material.
20Objectives 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.
21Vectors of Viral Diseases Section 2 Viral DiseasesChapter 24Vectors of Viral DiseasesVectors, or hosts, of viral diseases include humans, animals, and insects.
22Section 2 Viral Diseases Chapter 24Human Viral DiseasesViruses cause many human diseases, including the common cold, flu, hepatitis, rabies, chickenpox, certain types of cancer, and AIDS.
23Human Viral Diseases, continued Section 2 Viral DiseasesChapter 24Human Viral Diseases, continuedChickenpox and ShinglesChickenpox and shingles are caused by the same varicella-zoster herpesvirus.
24Human Viral Diseases, continued Section 2 Viral DiseasesChapter 24Human Viral Diseases, continuedViral HepatitisHepatitis, 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.
25Human Viral Diseases, continued Section 2 Viral DiseasesChapter 24Human Viral Diseases, continuedAcquired 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.
28Human Viral Diseases, continued Section 2 Viral DiseasesChapter 24Human Viral Diseases, continuedViruses and CancerSome viruses contain oncogenes that can cause cancer, while other viruses convert proto-oncogenes, which usually control cell growth, to oncogenes.
29Emerging Viral Diseases Section 2 Viral DiseasesChapter 24Emerging Viral DiseasesEmerging viruses usually infect animals isolated in nature but can jump to humans when contact occurs in the environment.
30Prevention and Treatment Section 2 Viral DiseasesChapter 24Prevention and TreatmentVaccinationsA 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.
31Prevention and Treatment, continued Section 2 Viral DiseasesChapter 24Prevention and Treatment, continuedVector ControlControl efforts, including killing mosquitoes and other vectors and quarantining ill patients, have helped reduce the spread of certain viral diseases.
32Prevention and Treatment, continued Section 2 Viral DiseasesChapter 24Prevention and Treatment, continuedDrug TherapyAntibiotics are ineffective against viral diseases.Viral drugs, such as acyclovir, block specific steps in viral replication.
33Section 2 Viral Diseases Chapter 24Virods and PrionsViroids 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.