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TORTORA • FUNKE • CASE Microbiology Differentiate between a virus and a bacterium. AN INTRODUCTION EIGHTH EDITION B.E Pruitt & Jane J. Stein Viruses may be regarded as exceptionally complex aggregations of nonliving chemicals OR exceptionally simple living microbes. Chapter 13 Viruses, Viroids, and Prions PowerPoint® Lecture Slide Presentation prepared by Christine L. Case Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viruses (range from 20 to 1000 nm) Viruses nm = 10-9 m • Viruses contain DNA or RNA • And a protein coat • Some are enclosed by an envelope (lipids, proteins, and carbohydrates) • Some viruses have spikes • Most viruses infect only specific types of cells in one host • Host range is determined by specific host attachment sites and cellular factors • Obligatory intracellular parasites, causing synthesis of specialized elements that transfer viral nucleic acid to other cells. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Nonenveloped Polyhedral Viruses Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.1 Enveloped Helical Virus Describe the chemical composition and physical structure of an enveloped and a nonenveloped virus. Virion = complete, fully developed viral particle of nucleic acid surrounded by a coat Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.2a, b Viruses contain either DNA or RNA, but never both. Nucleic acid may be single or double stranded, linear or circular, or divided into several separate Copyright © 2004 molecules. Pearson Education, Inc., publishing as Benjamin Cummings 1 Helical Viruses Complex Viruses • Capsid – protein coat surrounding nucleic acid • Composed of capsomeres, single or multiple proteins Helical viruses look like long or coiled threads. Their capsids are hollow cylinders surrounding the DNA/RNA. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.4a, b Viral Taxonomy Define viral species. • Classification based on type of nucleic acid, replication, and morphology. • Family names end in -viridae • Genus names end in -virus • Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species Figure 13.5a Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Viral Taxonomy Give an example of a family, genus, and common name for a virus. • Herpesviridae • Retroviridae • Herpesvirus • Lentivirus • Human herpes virus 1, HHV 2, HHV 3 • Human Immunodeficiency Virus 1, HIV 2 • Subspecies are designated by a number Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 2 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Growing Viruses Growing Viruses Describe how animal viruses are cultured. Describe how bacteriophages are cultured. • Viruses must be grown in living host cells. • Viruses must be grown in living cells. • Animal viruses may be grown in living animals or in embryonated eggs. • Bacteriophages form plaques (clearings) on a lawn of bacteria. • Easiest to grow Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.6 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.7 Cytopathic effect of viruses Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. • Cytopathic effects due to viral growth Uninfected mouse cells form monolayer (left). Infected cells 24 hours later pile up and round up (right). Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.8 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.9 3 Virus Identification Multiplication of Bacteriophages (Lytic Cycle) List three techniques that are used to identify viruses. • Serological tests • Detect antibodies against viruses in a patient • Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot • Nucleic acids • Attachment Phage attaches by tail fibers to host cell • Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell • Biosynthesis Production of phage DNA and proteins • Maturation Assembly of phage particles • Release Phage lysozyme breaks cell wall • RFLPs – restriction fragment length polymorphisms • PCR – polymerase chain reaction (used to identify West Nile virus in U.S. in 1999) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Lytic cycle of T-even bacteriophage Bacterial cell wall Bacterial chromosome Capsid Lytic cycle of T-even bacteriophage Burst time is generally about 20 – 40 minutes after phage absorption. Burst size ranges from 50 to 200 new phage cells. DNA Capsid Tail DNA Sheath Tail fiber 1 Attachment: Base plate Pin Cell wall Phage attaches to host cell. Tail Plasma membrane 4 Maturation: Viral components are assembled into virions. Capsid 2 Penetration: Phage penetrates host cell and injects its DNA. Sheath contracted 5 Release: Host cell lyses and new virions are released. Tail core Tail fibers 3 Merozoites released into bloodstream from liver may infect new red blood cells Describe the lytic cycle of T-even bacteriophages. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10.1 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10.2 One-step Growth Curve for bacteriophage • Lytic cycle Phage causes lysis and death of host cell • Lysogenic cycle Prophage DNA incorporated in host DNA During biosynthesis and maturation, separate components of DNA and protein may be detected in the host cell. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.11 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 4 The Lysogenic Cycle – bacteriophage lambda in E.coli Describe the lysogenic cycle of bacteriophage lambda. Specialized Transduction Prophage gal gene Bacterial DNA 1 Prophage exists in galactose-using host (containing the gal gene). Galactose-positive donor cell gal gene 2 Phage genome excises, carrying with it the adjacent gal gene from the host. 3 Phage matures and cell lyses, releasing phage carrying gal gene. gal gene 4 Phage infects a cell that cannot utilize galactose (lacking gal gene). Galactose-negative recipient cell 5 Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 6 Lysogenic cell can now metabolize galactose. Galactose-positive recombinant cell Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.12 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.13 Multiplication of Animal viruses Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • Attachment Viruses attaches to cell membrane • Penetration By endocytosis or fusion • Uncoating By viral or host enzymes • Biosynthesis Production of nucleic acid and proteins • Maturation Nucleic acid and capsid proteins assemble • Release By budding (enveloped viruses) or rupture Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Attachment, Penetration, and Uncoating Compare and contrast the multiplication cycle of DNA- and RNA-containing animal viruses. Entry of herpes simplex virus into an animal cell. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.14 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 5 Multiplication of Papovarius, a DNA-containing Virus Papovavirus 1 Virion attaches to host cell 7 Virions are released Host cell DNA Capsid 2 Virion penetrates DNA cell and its DNA is uncoated Cytoplasm 6 Virions mature Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 4 Late transcription; DNA is replicated Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 3 Early transcription and translation; enzymes are synthesized DNA-containing animal viruses: individual capsomeres visible Figure 13.15 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Pathways of Multiplication for RNA-Containing Viruses DNA-containing animal viruses: envelop around this herpes simplex virus broken (fried egg appearance) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.17 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Multiplication & Inheritance in a Retrovirus Capsid Reverse transcriptase DNA Virus Two identical + stands of RNA 1 Retrovirus penetrates host cell. Host cell DNA of one of the host cell’s chromosomes 5 Mature retrovirus leaves host cell, acquiring an envelope as it buds out. Identical strands of RNA Viral proteins RNA RNA-containing animal viruses: rubella (left), mouse mammary tumor virus (right). Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Reverse transcriptase Viral RNA 4 Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins. Provirus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 2 Virion penetrates cell and its DNA is uncoated 3 The new viral DNA is transported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA. Figure 13.19 6 Release of an enveloped virus by budding Most enveloped viruses take part of host’s plasma membrane for their envelope. Cancer Define oncogene and transformed cell. • Activated oncogenes transform normal cells into cancerous cells. (malignant transformation) • Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens, chromosome abnormalities, can produce tumors when injected into susceptible animals. • Several DNA viruses and retroviruses are oncogenic. • The genetic material of oncogenic viruses becomes integrated into the host cell's DNA. Figure 13.20 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Oncogenic Viruses Discuss the relationship of DNA- and RNA-containing viruses to cancer. Provide an example of a latent viral infection. • Latent Viral Infections • Oncogenic DNA Viruses • Adenoviridae • Oncogenic RNA viruses • Retroviridae • Papovaviridae • Viral RNA is transcribed to DNA which can integrate into host DNA • Hepadnaviridae • HTLV 1 • Heresviridae • Poxviridae • HTLV 2 •Retroviruses carry reverse transcriptase which allows RNA to DNA, permitting oncogenic properties Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • Virus remains in asymptomatic host cell for long periods • Cold sores, shingles • Persistent Viral Infections • Disease processes occurs over a long period, generally fatal • Subacute sclerosing panencephalitis (measles virus) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Prions Differentiate between persistant viral infections and latent viral infections. Discuss how a protein can be infectious. • Infectious proteins first discovered in 1980’s • Inherited and transmissible by ingestion, transplant, & surgical instruments • Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-SträusslerScheinker syndrome, fatal familial insomnia, mad cow disease • PrPC, normal cellular prion protein, on cell surface •Persistent viral infections are caused by conventional viruses, occur over a long period, generally fatal. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • PrPSc, scrapie protein, accumulate in brain cells forming plaques Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 7 Prions Some Plant Viruses How a protein can be infectious: if an abnormal prion protein enters cell, it changes a normal prion to PrPSc, which changes another normal PrP (accumulation of abnormal PrPSc) Name a virus that causes a plant disease. PrPSc PrPc 2 1 3 4 Lysosome Endosome 5 6 7 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 8 Figure 13.21 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Table 13.6 Linear and circular potato spindle tuber viroid Differentiate between virus, viroid, and prion. • Plant Viruses Virus Families • Plant viruses enter through wounds or via insects • Single-stranded DNA, nonenveloped viruses • Viroids • Parvoviridae • Viroids are infectious RNA; potato spindle tuber disease • Human parvovirus • Fifth disease • Anemia in immunocompromised patients • Prion = infectious protein Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.22 Double-stranded DNA, nonenveloped viruses • Mastadenovirus • Respiratory infections in humans • Tumors in animals Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Double-stranded DNA, nonenveloped viruses • Papillomavirus (human wart virus) • Polyomavirus • Cause tumors, some cause cancer Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 8 Double-stranded DNA, nonenveloped viruses Double-stranded DNA, nonenveloped viruses • Simplexvirus (HHV1 and HHV 2) • Orthopoxvirus (vaccinia and smallpox viruses) • Molluscipoxvirus • Smallpox, molluscum contagiosum, cowpox Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Double-stranded DNA, nonenveloped viruses • Hepadnavirus (Hepatitis B virus) • Use reverse transcriptase to produce DNA from mRNA Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, + strand, nonenveloped • Varicellavirus (HHV 3) • Lymphocryptovirus (HHV 4) • Cytomegalovirus (HHV 5) • Roseolovirus (HHV 6) • HHV 7 • Kaposi's sarcoma (HHV 8) • Some herpesviruses can remain latent in host cells Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, + strand, nonenveloped • Enterovirus • Enteroviruses include poliovirus and coxsackievirus • Rhinovirus • Hepatitis A virus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, + strand, nonenveloped • Alphavirus • Hepatitis E virus • Norovirus (Norwalk agent) causes gastroenteritis Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • Alphaviruses are transmitted by arthropods; include EEE, WEE • Rubivirus (rubella virus) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 9 Single-stranded RNA, + strand, nonenveloped • Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses • Hepatitis C virus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, – strand, one RNA strand • Vesiculovirus • Lyssavirus (rabies virus) • Cause numerous animal diseases Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, – strand, one RNA strand Single-stranded RNA, + strand, nonenveloped • Coronavirus • Upper respiratory infections Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, – strand, one RNA strand • Filovirus • Enveloped, helical viruses • Ebola and Marburg viruses Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, – strand, one RNA strand • Paramyxovirus • Morbillivirus • Paramyxovirus causes parainfluenza, mumps and Newcastle disease Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings • Hepatitis D virus • Depends on coinfection with Hepadnavirus Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 10 Single-stranded RNA, – strand, multiple RNA strands Single-stranded RNA, – strand, multiple RNA strands • Influenzavirus (Influenza viruses A and B) • Bunyavirus (CE virus) • Influenza C virus • Hantavirus • Envelope spikes can agglutinate RBCs Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, – strand, multiple RNA strands • Arenavirus • Helical capsids contain RNAcontaining granules • Lymphocytic choriomeningitis • VEE and Lassa Fever Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Single-stranded RNA, two RNA strands, produce DNA • Lentivirus (HIV) • Oncogenic viruses • Use reverse transcriptase to produce DNA from viral genome • Includes all RNA tumor viruses Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Double-stranded RNA, nonenveloped • Reovirus (Respiratory Enteric Orphan) • Rotavirus • Mild respiratory infections and gastroenteritis • Colorado tick fever Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings 11