TORTORA • FUNKE • CASE Microbiology - Bethel College · PDF file ·...

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

PowerPoint® Lecture Slide Presentation prepared by Christine L. Case

MicrobiologyB.E Pruitt & Jane J. Stein

AN INTRODUCTIONEIGHTH EDITION

TORTORA • FUNKE • CASE

Chapter 13Viruses, Viroids, and Prions


Differentiate between a virus and a bacterium.

Viruses may be regarded as exceptionally complex aggregations of nonliving chemicals OR exceptionally simple living microbes.


Viruses• 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.


Viruses (range from 20 to 1000 nm)

Figure 13.1

nm = 10-9 m


Nonenveloped Polyhedral Viruses

Figure 13.2a, b

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


Enveloped Helical Virus

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 molecules.

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Helical Viruses

Figure 13.4a, b

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

Complex Viruses

Figure 13.5a

• Capsid – protein coat surrounding nucleic acid

• Composed of capsomeres, single or multiple proteins


Viral Taxonomy

• 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

• Subspecies are designated by a number

Define viral species.


Viral Taxonomy

• Herpesviridae• Herpesvirus• Human herpes

virus 1, HHV 2, HHV 3

• Retroviridae• Lentivirus• Human

Immunodeficiency Virus 1, HIV 2

Give an example of a family, genus, and common name for a virus.

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

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Growing Viruses

• Viruses must be grown in living cells.• Bacteriophages

form plaques (clearings) on a lawn of bacteria.

• Easiest to grow

Figure 13.6

Describe how bacteriophages are cultured.


Growing Viruses

• Viruses must be grown in living host cells.

• Animal viruses may be grown in living animals or in embryonated eggs.

Figure 13.7

Describe how animal viruses are cultured.


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

Figure 13.8 Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Cytopathic effect of viruses

Figure 13.9

Uninfected mouse cells form monolayer (left). Infected cells 24 hours later pile up and round up (right).

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• Serological tests• Detect antibodies against viruses in a patient• Use antibodies to identify viruses in neutralization

tests, viral hemagglutination, and Western blot• Nucleic acids

• RFLPs – restriction fragment length polymorphisms• PCR – polymerase chain reaction (used to identify

West Nile virus in U.S. in 1999)

Virus Identification

List three techniques that are used to identify viruses.


• 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

Multiplication of Bacteriophages (Lytic Cycle)

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10.1

Attachment:Phage attaches to host cell.

Penetration:Phage penetrates host cell and injects its DNA.

Merozoites released into bloodstream from liver may infect new red blood cells

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2

3

Bacterial cell wall

Bacterial chromosome

Capsid DNA

Capsid

SheathTail fiberBase platePinCell wall

Tail

Plasma membrane

Sheath contracted

Tail core

Lytic cycle of T-even bacteriophage

Describe the lytic cycle of T-even bacteriophages.Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10.2

4 Maturation:Viral components are assembled into virions.

Tail

5 Release:Host cell lyses and new virions are released.

DNA

Capsid

Tail fibers

Lytic cycle of T-even bacteriophageBurst time is generally about 20 – 40 minutes after phage absorption. Burst size ranges from 50 to 200 new phage cells.


One-step Growth Curve for bacteriophage

Figure 13.11

During biosynthesis and maturation, separate components of DNA and protein may be detected in the host cell.


• Lytic cycle Phage causes lysis and death of host cell

• Lysogenic cycle Prophage DNA incorporated in host DNA

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The Lysogenic Cycle – bacteriophage lambda in E.coli

Figure 13.12

Describe the lysogenic cycle of bacteriophage lambda.


Specialized Transduction

Figure 13.13

Prophage exists in galactose-using host (containing the gal gene).

Phage genome excises, carrying with it the adjacent gal gene from the host.

Phage matures and cell lyses, releasing phage carrying gal gene.

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2

3

Prophage

gal gene

gal gene Bacterial DNA

Galactose-positive donor cell gal gene

Phage infects a cell that cannot utilize galactose (lacking gal gene).

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Galactose-negative recipient cell

Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA.

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Lysogenic cell can now metabolize galactose.

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Galactose-positive recombinant cell


• 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

Multiplication of Animal viruses


Attachment, Penetration, and Uncoating

Figure 13.14

Entry of herpes simplex virus into an animal cell.


Compare and contrast the multiplication cycle of DNA- and RNA-containing animal viruses.

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Multiplication of Papovarius, a DNA-containing Virus

Figure 13.15

Virion attaches to host cell

Virion penetrates cell and its DNA is uncoated

Early transcription and translation; enzymes are synthesized

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2

3

DNA

Late transcription; DNA is replicated

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Late translation; capsid proteins are synthesized

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Virions mature6

Capsid

Papovavirus

Host cell

DNACytoplasm

Virions are released7

Capsid proteins

mRNA


DNA-containing animal viruses: individual capsomeres visible


DNA-containing animal viruses: envelop around this herpes simplex virus broken (fried egg appearance) Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Pathways of Multiplication for RNA-Containing Viruses

Figure 13.17


RNA-containing animal viruses: rubella (left), mouse mammary tumor virus (right).


Multiplication & Inheritance in a Retrovirus

Figure 13.19

Retrovirus penetrates host cell.

Virion penetrates cell and its DNA is uncoated

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.

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2

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DNA

Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins.

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Mature retrovirus leaves host cell, acquiring an envelope as it buds out.

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CapsidReverse transcriptase

Virus Two identical + stands of RNA

DNA of one of the host cell’s chromosomes

Provirus

Host cell

Reverse transcriptase

Viral RNA

RNA

Viral proteins

Identical strands of RNA

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Release of an enveloped virus by budding

Figure 13.20

Most enveloped viruses take part of host’s plasma membrane for their envelope.


• 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.

Cancer

Define oncogene and transformed cell.


• Oncogenic DNA Viruses• Adenoviridae• Heresviridae• Poxviridae• Papovaviridae• Hepadnaviridae

Oncogenic Viruses

• Oncogenic RNA viruses• Retroviridae

• Viral RNA is transcribed to DNA which can integrate into host DNA

• HTLV 1• HTLV 2

Discuss the relationship of DNA- and RNA-containing viruses to cancer.

•Retroviruses carry reverse transcriptase which allows RNA to DNA, permitting oncogenic properties


• Latent Viral Infections• 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)

Provide an example of a latent viral infection.


Differentiate between persistant viral infections and latent viral infections.

•Persistent viral infections are caused by conventional viruses, occur over a long period, generally fatal.


• Infectious proteins first discovered in 1980’s• Inherited and transmissible by ingestion, transplant, &

surgical instruments• Spongiform encephalopathies: Sheep scrapie,

Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease

• PrPC, normal cellular prion protein, on cell surface• PrPSc, scrapie protein, accumulate in brain cells

forming plaques

Prions

Discuss how a protein can be infectious.

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Prions

Figure 13.21

PrPc

PrPSc

1 2 3 4

5 6 7 8

Endosome

Lysosome

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)


Some Plant Viruses

Table 13.6

Name a virus that causes a plant disease.

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.22

• Plant Viruses• Plant viruses

enter through wounds or via insects

• Viroids• Viroids are

infectious RNA; potato spindle tuber disease

• Prion = infectious protein

Linear and circular potato spindle tuber viroid

Differentiate between virus, viroid, and prion.


Virus Families

• Single-stranded DNA, nonenveloped viruses• Parvoviridae

• Human parvovirus• Fifth disease

• Anemia inimmunocompromisedpatients


Double-stranded DNA, nonenveloped viruses

• Mastadenovirus• Respiratory

infections in humans

• Tumors in animals



• Papillomavirus(human wart virus)

• Polyomavirus• Cause tumors,

some cause cancer

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• Orthopoxvirus(vaccinia and smallpox viruses)

• Molluscipoxvirus• Smallpox,

molluscum contagiosum, cowpox


• Simplexvirus (HHV1 and HHV 2)

• 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




• Hepadnavirus(Hepatitis B virus)• Use reverse

transcriptase to produce DNA frommRNA


Single-stranded RNA, + strand, nonenveloped

• Enterovirus• Enteroviruses

include poliovirus and coxsackievirus

• Rhinovirus• Hepatitis A virus



• Hepatitis E virus

• Norovirus (Norwalk agent) causes gastroenteritis



• Alphavirus• Alphaviruses are

transmitted by arthropods; include EEE, WEE

• Rubivirus (rubella virus)

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

• Hepatitis C virus



• Coronavirus• Upper respiratory

infections


Single-stranded RNA, – strand, one RNA strand

• Vesiculovirus • Lyssavirus (rabies

virus)• Cause numerous

animal diseases



• Filovirus• Enveloped,

helical viruses• Ebola and

Marburg viruses



• Paramyxovirus• Morbillivirus

• Paramyxoviruscausesparainfluenza, mumps and Newcastle disease



• Hepatitis D virus• Depends on

coinfection withHepadnavirus

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• Influenzavirus(Influenza viruses A and B)

• Influenza C virus• Envelope spikes

can agglutinateRBCs

Single-stranded RNA, –strand, multiple RNA strands


• Bunyavirus (CE virus)• Hantavirus



• Arenavirus• Helical capsids

contain RNA-containing granules

• Lymphocytic choriomeningitis

• VEE and LassaFever



• Lentivirus (HIV)• Oncogenic viruses

• Use reverse transcriptase to produce DNA from viral genome

• Includes all RNA tumor viruses

Single-stranded RNA, two RNA strands, produce DNA


Double-stranded RNA, nonenveloped

• Reovirus (Respiratory Enteric Orphan)

• Rotavirus• Mild respiratory

infections and gastroenteritis

• Colorado tick fever

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