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.

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Nonenveloped Polyhedral Viruses

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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

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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

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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

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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

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Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

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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

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Figure 13.6

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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

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Figure 13.9

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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)

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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.

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Figure 13.10.1

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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

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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

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Figure 13.13

Multiplication of Animal viruses

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• 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

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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.

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Figure 13.14

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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

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3 Early transcription and

translation; enzymes are synthesized

DNA-containing animal viruses: individual capsomeres visible Figure 13.15

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Pathways of Multiplication for RNA-Containing Viruses

DNA-containing animal viruses: envelop around this herpes simplex virus broken (fried egg appearance)

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Figure 13.17

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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

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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

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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

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• 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)

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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

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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

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Figure 13.21

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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

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Double-stranded DNA, nonenveloped viruses

• Papillomavirus (human wart virus) • Polyomavirus • Cause tumors, some cause cancer

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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

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Double-stranded DNA, nonenveloped viruses

• Hepadnavirus (Hepatitis B virus) • Use reverse transcriptase to produce DNA from mRNA

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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

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Single-stranded RNA, + strand, nonenveloped

• Alphavirus • Hepatitis E virus • Norovirus (Norwalk agent) causes gastroenteritis

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• Alphaviruses are transmitted by arthropods; include EEE, WEE • Rubivirus (rubella virus)

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Single-stranded RNA, + strand, nonenveloped

• Arboviruses can replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses • Hepatitis C virus

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Single-stranded RNA, – strand, one RNA strand

• Vesiculovirus • Lyssavirus (rabies virus) • Cause numerous animal diseases

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Single-stranded RNA, – strand, one RNA strand

Single-stranded RNA, + strand, nonenveloped

• Coronavirus • Upper respiratory infections

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Single-stranded RNA, – strand, one RNA strand

• Filovirus • Enveloped, helical viruses • Ebola and Marburg viruses

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Single-stranded RNA, – strand, one RNA strand

• Paramyxovirus • Morbillivirus • Paramyxovirus causes parainfluenza, mumps and Newcastle disease

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• Hepatitis D virus • Depends on coinfection with Hepadnavirus

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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

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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

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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

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Double-stranded RNA, nonenveloped

• Reovirus (Respiratory Enteric Orphan) • Rotavirus • Mild respiratory infections and gastroenteritis • Colorado tick fever

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