VirusesViruses A virus is A virus is notnot a cell. It lives only within a cell. It lives only within

a living cell and has no attributes of a a living cell and has no attributes of a living organism. living organism.

It is an obligate intracellular parasite.It is an obligate intracellular parasite.

VirusesViruses A virus is A virus is notnot a cell. It lives only within a cell. It lives only within

a living cell and has no attributes of a a living cell and has no attributes of a living organism. living organism.

It is an obligate intracellular parasite.It is an obligate intracellular parasite.

Review!What does obligate mean?

Capable of functioning or surviving only in a particular condition What is a parasite?

Organism that lives and derives nourishment at the detriment of the hostWhat is an obligate parasite?

VirusesViruses It is made up of DNA or RNA inside It is made up of DNA or RNA inside

a protein coat called a capsid.a protein coat called a capsid.

RNA

VirusVirus Some take lipids from the cell it infects Some take lipids from the cell it infects

and make a covering over the capsid and make a covering over the capsid that has glycoprotein receptors.that has glycoprotein receptors.

Receptors are used to attach to the Receptors are used to attach to the host’s membrane.host’s membrane.

RNA

Virus StructureVirus Structure

VirusesViruses A virus is A virus is notnot a cell a cell It is made up of genetic material inside It is made up of genetic material inside

a protein coata protein coat Viruses Viruses

do not do not carry on carry on most most metabolic metabolic activitiesactivities

VirusesViruses

Viruses that attack Viruses that attack only bacteria are only bacteria are known as known as bacteriophages.bacteriophages.

Virus Reproduction – Lytic CycleVirus Reproduction – Lytic Cycle

AttachmentAttachment Phage attaches by tail fibers to Phage attaches by tail fibers to

host cellhost cell PenetrationPenetration Phage lysozyme opens cell Phage lysozyme opens cell

wall, wall, tail sheath contracts to force tail sheath contracts to force

tail tail core and DNA into cellcore and DNA into cell

BiosynthesisBiosynthesis Production of phage DNA Production of phage DNA and proteinsand proteins

MaturationMaturation Assembly of phage particlesAssembly of phage particles ReleaseRelease Phage lysozyme breaks cell Phage lysozyme breaks cell

wallwall

Multiplication of Multiplication of Bacteriophages (Lytic Cycle)Bacteriophages (Lytic Cycle)

Virus Reproduction – Lysogenic CycleVirus Reproduction – Lysogenic Cycle

Lytic or Lysogenic Cycle?Lytic or Lysogenic Cycle?

The animation on The animation on

the next slide the next slide demonstrates which demonstrates which

cycle?cycle?

Lytic vs LysogenicLytic vs Lysogenic

Lytic cycleLytic cycle– Phage causes lysis and death of Phage causes lysis and death of

host cellhost cell

Lysogenic cycleLysogenic cycle– Prophage DNA incorporated in Prophage DNA incorporated in

host DNAhost DNA

Virus Classification

Smallpox Although smallpox was

declared extinct in the wild in 1979 (last natural infection recorded in 1977) there is increasing concern about its potential use as a biological weapon. Although only two locations officially hold variola (one at the CDC in the USA and one in Russia) it is feared that secret stockpiles exist.

Smallpox

CLASSIFICATION OF THE SMALLPOX VIRUS

GENOME: Linear Double Stranded DNA

Family: Poxviridae Subfamily: Chordopoxvirinae Genus: Orthopoxvirus Species: Variola

Prions and Viroids

Bits and Pieces that cause Bits and Pieces that cause diseasedisease

1818

ViroidsViroidsSmall, circular Small, circular RNARNA molecules molecules without a protein without a protein coatcoatInfect Infect plantsplantsPotato faminePotato famine in in IrelandIrelandResemble intronsResemble introns cut out of cut out of eukaryoticeukaryotic

copyright cmassengalecopyright cmassengale

1919

PrionsPrionsPrions are Prions are “infectious “infectious proteins”proteins” They are normal body They are normal body proteins that get proteins that get converted into an converted into an alternate configurationalternate configuration by by contact with other prion contact with other prion proteinsproteins They have They have no DNA or no DNA or RNARNAThe main protein The main protein involved in human and involved in human and mammalian prion mammalian prion diseasesdiseases is called is called “PrP”“PrP”copyright cmassengalecopyright cmassengale

2020

Prion Prion DiseasesDiseases

Prions form Prions form insoluble insoluble deposits in the braindeposits in the brainCauses neurons to Causes neurons to rapidly degenerate.rapidly degenerate.Mad cow diseaseMad cow disease (bovine spongiform (bovine spongiform encephalitis: BSE) is an encephalitis: BSE) is an exampleexamplePeople in New Guinea People in New Guinea used to suffer from used to suffer from kurukuru, which they got , which they got from eating the brains from eating the brains of their enemiesof their enemiescopyright cmassengalecopyright cmassengale

Virus ReproductionVirus Reproduction

Negative Virus InfluencesNegative Virus Influences They cause infections in both They cause infections in both

plants and animalsplants and animals Some viruses cause tumors and wartsSome viruses cause tumors and warts They also destroy cells and are They also destroy cells and are

responsible for human diseases such asresponsible for human diseases such as– poliopolio– measlesmeasles– mumpsmumps– influenzainfluenza– hepatitishepatitis– coldscolds– AIDSAIDS

Human Papilloma Virus - Warts Influenza Virus - Flu

Human Immunodeficiency VirusAIDS

Rabies Virus

Positive Virus InfluencesPositive Virus Influences Certain viruses are Certain viruses are

used in the control used in the control of insect pestsof insect pests

Others are used in Others are used in genetic researchgenetic research

Scientists have been Scientists have been able to use viruses to able to use viruses to biologically control biologically control caterpillars of the European caterpillars of the European pine sawfly and the gypsy pine sawfly and the gypsy mothmoth