Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ebola virus disease wikipedia , lookup
Marburg virus disease wikipedia , lookup
Bioterrorism wikipedia , lookup
Human cytomegalovirus wikipedia , lookup
Henipavirus wikipedia , lookup
Hepatitis B wikipedia , lookup
Orthohantavirus wikipedia , lookup
Influenza A virus wikipedia , lookup
Slide 1 ___________________________________ ___________________________________ ___________________________________ 6 ___________________________________ Viruses ___________________________________ At the Threshold of Life ___________________________________ ___________________________________ Slide 2 Looking Ahead ___________________________________ ___________________________________ • On completing this chapter, you should be able to: – Explain the events leading to the discovery of viruses and recognize some turning points in the development of virology; – Appreciate the distinctive structure of viruses, including their incredibly small size and relatively simple components; – describe the stages and details of the replication process exhibited by viruses; – Explain the significance of viral replication with respect to the disease process and the development of resistance to viral disease; ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 3 Looking Ahead • On completing this chapter, you should be able to: – Identify some methods for controlling viruses and for using viruses to benefit society; – Recognize the existence of certain types of subviral particles; – Summarize the development of cancer and understand the involvement of viruses in this dreaded disease. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 4 ___________________________________ What is life ___________________________________ • Is cellular • Growth ___________________________________ – Increase in numbers by reproducing – Increase in size ___________________________________ • Has metabolic processes – Uses energy – Excretes waste products ___________________________________ • Can respond to its environment ___________________________________ ___________________________________ Slide 5 ___________________________________ The Nature of Viruses ___________________________________ • Not really alive – Lack the capacity to perform any of the life processes on their own. • Not really completely inert – When in the presence of a target cell they will attach and incorporate their DNA or RNA into the cells function. • Existence somewhere between living objects and chemical compounds ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 6 The Discovery and Structure of Viruses • The development of virology ___________________________________ – 1892 Dmitri Iwanoski • Tobacco mosaic virus (TMV) • Bacteria-free filtrate still infectious ___________________________________ – Viruses were small enough to get past the filter. • 1898 Martinus Beijerinck supported these data ___________________________________ – 1930s Wendell Stanley ___________________________________ • Crystals of TMV – 1933 Ernst Ruska • Invention of electron microscope – Finally allowed visualization of viruses ___________________________________ © National Library of Medicine Dmitri Iwanowski ___________________________________ ___________________________________ Slide 7 The Discovery and Structure of Viruses • ___________________________________ The structure of viruses – Size • As small as 27 nm (0.027 mM); poliovirus • Some as large as 250 nm (0.25 mM); smallpox • At least 500 could fit inside single bacterium! ___________________________________ ___________________________________ ___________________________________ Figure 6.2: Size relationships among microbes ___________________________________ ___________________________________ ___________________________________ Slide 8 The Discovery and Structure of Viruses • The structure of viruses ___________________________________ ___________________________________ – Symmetry • Helix • Icosahedron • Complex ___________________________________ Courtesy of Dr. Sara Miller, Duke University Medical Center. ___________________________________ ___________________________________ ___________________________________ Fig. 6.5 ___________________________________ Slide 9 The Discovery and Structure of Viruses ___________________________________ • The components of viruses – Minimum of nucleic acid and protein coat – Nucleic acid • • • • • Genome RNA or DNA, not both Segmented or non-segmented Circular or linear Single-stranded or double-stranded ___________________________________ ___________________________________ Fig. 6.4a: naked Icosahedral virus ___________________________________ – Protein ___________________________________ • Capsid (a coat surrounding the Nucleic acid) – Made of Capsomeres – Nucelocapsid: a combination of the nucleic acide and the protein capsid. This is a complete virus. Fig. 6.4b: A naked helical virus ___________________________________ ___________________________________ Slide 10 The Discovery and Structure of Viruses • The components of viruses ___________________________________ ___________________________________ – Some viruses have an Envelope • Often made of Lipids taken from the host cell • Often contains surface spikes which allow adhesion ___________________________________ – No cytoplasm – No metabolism – No increase or decrease in size ___________________________________ ___________________________________ ___________________________________ Fig. 6.4 Icosahedral and helical viruses ___________________________________ Slide 11 ___________________________________ Viral Replication ___________________________________ • The stages of replication – Attachment • Binding to receptor site on target cell ___________________________________ – Penetration • Fusion and entry of target cell – Uncoating ___________________________________ • Release of genome into cell – Synthesis • Program of viral gene expression • Translation of viral proteins ___________________________________ – Assembly • Putting all newly synthesized parts together – Release • New viruses exit infected cell, leaving spent, dead cell behind ___________________________________ ___________________________________ Slide 12 ___________________________________ Viral Replication: Lytic Cycle ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 6.7: Replication of a DNA virus ___________________________________ ___________________________________ Slide 13 Viral Replication • When viruses don’t replicate – Lysogeny • Integration of viral genome into host’s genome • Viral genome become dormant • Integrated viral genome is known as provirus • Human equivalents are HIV, herpes, • Typical for many plant viruses Figure 6.9: The formation of a provirus ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 14 Viral Replication ___________________________________ ___________________________________ • Viral replication and disease – Destruction of healthy cells – Viral hepatitis • Destruction of liver cells by infection • Loss of liver function – AIDS • Destruction of immune cells • Loss of immune control over other infectious agents – Rabies • Destruction of nerves • Loss of control by nervous system ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 15 Viral Replication ___________________________________ ___________________________________ • Defense against viruses – Immune system • Antibodies (bind to and block the virus) • T cells (destroy cells infected with virus) – Antiviral drugs • Acyclovir • Amantadine • Azidothymidine (AZT) – Interferons • Released by infected cells this substance blocks the uptake of viruses in healthy cells. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 16 Viral Replication ___________________________________ ___________________________________ • Viral vaccines – Stimulation of immune response without risking pathogenic infection – Inactivated • Chemically destroyed virus • Example: Salk polio vaccine ___________________________________ – Attenuated • Live, but weakened virus • Example: Sabin polio vaccine – Genetically engineered • Production of viral proteins by recombinant organism • Example: Hepatitis B vaccine – Important part of combating bioterrorism • Example. Those immunized against smallpox would be immune if smallpox were used as a weapon. ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 17 Viral Replication • Viral cultivation – Difficult because viruses require a living organism to use its cellular processes. ___________________________________ ___________________________________ ___________________________________ • 1930s: Claud Johnson and Ernest Goodpasture – Growth of viruses in fertilized chicken eggs • 1940s cell culture (living human or other cells grown on a media) ___________________________________ – Derived from dispersed tissues • 1950s virus infection of cells in culture – Vaccine production • Diploid fibroblast cultures • Continuous cell line cultures ___________________________________ ___________________________________ ___________________________________ Slide 18 Viral Replication ___________________________________ ___________________________________ • Viruses as research tools – – – – Discovery of ribosome, mRNA functions Gene therapy delivery vehicles Vaccine agents Agricultural protection • Viruses and evolution – Presumed origin of viruses as normal cellular DNA or RNA – Viruses as agents that drive evolution • Incorporating viral DNA sometimes introduce a beneficial trait that can be passed on. ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 19 ___________________________________ Viral Replication ___________________________________ • Viroids and prions – Viroids ___________________________________ • Single-stranded RNA • No capsid • Infect plants – Prions Stanley Prusiner Proteinaceous infectious particles No nucleic acid Cause mad cow disease PrPc is normal cellular protein Change in conformation creates PrPsc Results in spongiform encephalopathy © Ulf Sirborn/AP Photos • • • • • • • Figure 6.11a: Stanley Prusiner, winner of 1997 Nobel in Physiology or Medicine for his work on prions as agents of infectious disease ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 20 ___________________________________ Viral Replication: Prions ___________________________________ ___________________________________ Courtesy of APHIS photo by Dr. Al Jenny/CDC Figure 6.11b: A photomicrograph of brain tissue showing vacuolar degeneration of gray matter characteristic of human and animal prion diseases ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 21 Viruses and Cancer ___________________________________ ___________________________________ • The development of cancer – Cancer • • • • Uncontrolled mitotic reproduction of cells Faster replication than normal cells Result is mass of cells called tumor Some known forms caused by viruses – Benign tumors (do not spread but that does not make them harmless) – Malignant tumors (those that spread) – Oncology (the study of cancer) – Dedifferentiation (cells lose their characteristics) – Loss of contact inhibition (continue to grow) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 22 Viruses and Cancer ___________________________________ ___________________________________ • The involvement of viruses – Carcinogens – Some viruses can induce tumors – Examples • Epstein-Barr virus (Burkitts Lymphoma) • Human T cell leukemia viruses (HTLVs) ___________________________________ ___________________________________ • How viruses transform cells – Michael Bishop and Harold Varmus • Oncogenes • Proto-oncogenes • How viruses may turn proto-oncogenes into oncogenes ___________________________________ ___________________________________ ___________________________________ Slide 23 Viruses and Cancer: How Viruses Transform Cells ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Figure 6.12: The oncogene theory ___________________________________ Slide 24 Summary •Know the definition of life and how a virus fits in. ___________________________________ ___________________________________ •Understand the structure of viruses •Understand the mechanism and types of viral replication •Understand the difficulties in culturing viruses ___________________________________ •Know the ways viruses disrupt cell function •How can viruses be used in research •What roles might viruses play in evolution •Describe a viroid and a prion •How can viruses function in cancers •Learn the related key terms in your text. ___________________________________ ___________________________________ ___________________________________ ___________________________________