VirusesViruses

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STRUCTURESTRUCTURE NonlivingNonliving Composed of a nucleic acid and a protein coatComposed of a nucleic acid and a protein coat Cause many diseasesCause many diseases Virology – Virology – Study of VirusesStudy of Viruses Comparison of Viruses and Cells belowComparison of Viruses and Cells below

Char. Of Char. Of LifeLife

VirusVirus CellCell

GrowthGrowth NoNo YesYes

HomeostasisHomeostasis NoNo YesYes

MetabolismMetabolism NoNo YesYes

MutationMutation YesYes YesYes

Nucleic acidNucleic acid DNA or RNADNA or RNA DNADNA

ReproductionReproduction Only within host cellOnly within host cell Independently Independently by cell divisionby cell division

StructureStructure Nucleic acid core, Nucleic acid core, protein covering, some protein covering, some have envelopehave envelope

Cytoplasm, cell Cytoplasm, cell membrane, etc..membrane, etc..

Nucleic acid (DNA or RNA)

Protein Coat ( capsid)

Structure of a Virus

Characteristics of VirusesCharacteristics of Viruses

2 essential features2 essential features 1. Nucleic Acid1. Nucleic Acid

May be DNA or RNAMay be DNA or RNA Helical, closed loop, or long strandHelical, closed loop, or long strand

2. Protein Coat – called CAPSID2. Protein Coat – called CAPSID Some have ENVELOPESome have ENVELOPE

Ex. Influenza, chickepox, herpes simplex, Ex. Influenza, chickepox, herpes simplex, HIVHIV

VIRAL SHAPEVIRAL SHAPE Icosahedron – 20 triangular facesIcosahedron – 20 triangular faces

Ex.) herpes, chickenpox, polioEx.) herpes, chickenpox, polio Helix – Coiled springHelix – Coiled spring

EX.)Rabies, measles, tobacco mosaicEX.)Rabies, measles, tobacco mosaic

Grouping VirusesGrouping Viruses Grouped according to:Grouped according to:

Presence of capsid and envelope – Presence of capsid and envelope – shapeshape RNA or DNA, single or double stranded – RNA or DNA, single or double stranded – structurestructure

Viral GroupViral Group Nucleic Nucleic AcidAcid

Shape and StructureShape and Structure ExampleExample

PapovavirusPapovaviruseses

DNADNA Icosahedral, non-env.Icosahedral, non-env. Warts, cancerWarts, cancer

AdenoviruseAdenovirusess

DNADNA Icosahedral, non-env.Icosahedral, non-env. Resp. & Resp. & intestinal intestinal infectionsinfections

HerpesvirusHerpesviruseses

DNADNA Icosahedral, Icosahedral, envelopedenveloped

Herpes Herpes simplex, simplex, chicken pox, chicken pox, mono, shinglesmono, shingles

PoxvirusesPoxviruses DNADNA Complex brick, Complex brick, envelopedenveloped

Small pox, cow Small pox, cow poxpox

PicornavirusPicornaviruseses

RNARNA Icosahedral, non-env.Icosahedral, non-env. Polio, hepatitis, Polio, hepatitis, cancercancer

MyxovirusesMyxoviruses RNARNA Helical, envelopedHelical, enveloped Influenza A, B, Influenza A, B, CC

RhabdovirusRhabdoviruseses

RNARNA Helical, envelopedHelical, enveloped RabiesRabies

RetrovirusesRetroviruses RNARNA Icosahedral, Icosahedral, envelopedenveloped

AIDS, cancerAIDS, cancer

Other Grouping of VirusesOther Grouping of Viruses

Viroids- The smallest known particle Viroids- The smallest known particle that can replicate.that can replicate. Disrupt plant cell metabolismDisrupt plant cell metabolism Can destroy entire cropsCan destroy entire crops

Prions – Abnormal forms of proteins that Prions – Abnormal forms of proteins that clump together inside cells.clump together inside cells. Clumping eventually kills the cellClumping eventually kills the cell ExamplesExamples

Scrapie – in sheepScrapie – in sheep Mad Cow DiseaseMad Cow Disease

Viral ReplicationViral Replication

Can replicate only by invading host cell Can replicate only by invading host cell and using its enzyme and organelles.and using its enzyme and organelles.

Bacteriophage – viruses that infect Bacteriophage – viruses that infect bacteriabacteria Used to study virusesUsed to study viruses

Lytic Cycle of Virus Lytic Cycle of Virus ReplicationReplication

Lytic CycleLytic Cycle Viral genome is released Viral genome is released

into the host cellinto the host cell Replication follows Replication follows

immediatelyimmediately Cellular components used Cellular components used

to make new virusesto make new viruses Viral enzyme kills cell.Viral enzyme kills cell. Play animationPlay animation

Lysogenic Cycle of Virus Lysogenic Cycle of Virus ReplicationReplication

Nucleic acid of virus becomes part of the Nucleic acid of virus becomes part of the host cell’s chromosomehost cell’s chromosome

Nucleic acid remains in the cell in this form Nucleic acid remains in the cell in this form for many generationsfor many generations

HIV follows this patternHIV follows this pattern HIV infects WBC and remains as provirusesHIV infects WBC and remains as proviruses As immune system fails, opportunistic As immune system fails, opportunistic

infections occur = AIDSinfections occur = AIDS Play animationPlay animation Play animationPlay animation

Viruses and Human DiseaseViruses and Human Disease Control and Prevention of spread.Control and Prevention of spread.

Vaccination & Antiviral drugsVaccination & Antiviral drugs Ex.) chickenpox vaccine, AZT, Acyclovir, protease Ex.) chickenpox vaccine, AZT, Acyclovir, protease

inhibitors.inhibitors.

Emerging Viruses – exist in isolated habitatsEmerging Viruses – exist in isolated habitats Do not usually infect humans unless Do not usually infect humans unless

environmental conditions favor contact.environmental conditions favor contact. Several viruses are now linked to cancers Several viruses are now linked to cancers

such as leukemia, liver cancer, Burkitt’s such as leukemia, liver cancer, Burkitt’s lymphoma, cervical cancer.lymphoma, cervical cancer.

PAPOVAVIRUSESPAPOVAVIRUSES

ADENOVIRUSESADENOVIRUSES

HERPESVIRUSESHERPESVIRUSES

POXVIRUSESPOXVIRUSES

PICORNAVIRUSPICORNAVIRUSESES

After polio infections, the killer T-cell have destroyed the motor

neurons that are producing the virus. The result is a loss of

muscle control including the

diaphragm. The iron lung changes the pressure to pump air

in and out of the lungs.

MYXOVIRUSMYXOVIRUSESES

RHABDOVIRUSESRHABDOVIRUSES

RETROVIRUSESRETROVIRUSES

Research the following Research the following virusesviruses

Viral GroupViral Group

PapovavirusePapovavirusessAdenovirusesAdenoviruses

HerpesviruseHerpesvirusess

PoxvirusesPoxviruses

PicornavirusePicornavirusessMyxovirusesMyxoviruses

RhabdoviruseRhabdovirusess

RetrovirusesRetroviruses

Look at how the virus infectsLook at how the virus infects

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