Viruses Viruses Discovery of VirusesDiscovery of Viruses

• Berijerinck Berijerinck (1897) (1897) coined the Latin name "virus"  meaning poison for  the coined the Latin name "virus"  meaning poison for  the

substance infecting tobacco plantssubstance infecting tobacco plants • Wendell StanleyWendell Stanley

(1935) crystallized sap from tobacco leaves infected (1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV) with Tobacco Mosaic Virus (TMV)

first person to see virusfirst person to see virus found virus was made of nucleic acid & proteinfound virus was made of nucleic acid & protein

• Edward Jenner Edward Jenner (1796) developed smallpox vaccine(1796) developed smallpox vaccine used pus from cowpoxused pus from cowpox

Viruses Viruses

Discovery of Viruses - ContinuedDiscovery of Viruses - Continued• Louis PasteurLouis Pasteur

Developed second vaccine against anthraxDeveloped second vaccine against anthrax Developed third vaccine against rabiesDeveloped third vaccine against rabies

• Used dried spinal cord of a rabbitUsed dried spinal cord of a rabbit

• SabinSabin Developed vaccine against polio that contained live Developed vaccine against polio that contained live

virusvirus Given orallyGiven orally

• SalkSalk Developed vaccine against polio using killed virusDeveloped vaccine against polio using killed virus Given as shotGiven as shot

Viruses Viruses

• Virology - study of virusesVirology - study of viruses • Deadly viruses are said to be virulentDeadly viruses are said to be virulent • Viruses couldn't be seen until electron Viruses couldn't be seen until electron

microscope inventedmicroscope invented • Viruses cause disease byViruses cause disease by

Killing cellsKilling cells Changing the rate of mitosis (warts, tumors, and Changing the rate of mitosis (warts, tumors, and

cancer)cancer)

Wendell Stanley and Leaf with TMVWendell Stanley and Leaf with TMV

Viral CharacteristicsViral Characteristics

Not living organismsNot living organisms NoncellularNoncellular Consist of Consist of

• a nucleic acid core (DNA or RNA) a nucleic acid core (DNA or RNA) • a protein coat called the capsida protein coat called the capsid• Some have a plasma membraneSome have a plasma membrane

Capsid made of protein subunits called Capsid made of protein subunits called capsomerescapsomeres

Cannot grow or replicate on their own Cannot grow or replicate on their own (inactive particles)(inactive particles)

Viral CharacteristicsViral Characteristics

Can only reproduce inside of a living host Can only reproduce inside of a living host cell using its raw materials & enzymescell using its raw materials & enzymes

Lack ribosomes & enzymes needed for Lack ribosomes & enzymes needed for protein synthesis or metabolismprotein synthesis or metabolism

Are extremely small particles ranging from Are extremely small particles ranging from 10 - 1400 nanometers on average10 - 1400 nanometers on average

Some can cause disease (smallpox, measles, Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, mononucleosis, influenza, colds, AIDS, Ebola)Ebola)

Viral CharacteristicsViral Characteristics

Some may also cause cancers such as Some may also cause cancers such as leukemiasleukemias

Virus free cells are rareVirus free cells are rare Highly host specific (only infect certain cells)Highly host specific (only infect certain cells) Referred to as phagesReferred to as phages Viruses are classified into 2 main groups by Viruses are classified into 2 main groups by

their nucleic acid --- DNA or RNA Virusestheir nucleic acid --- DNA or RNA Viruses   DNA & RNA viruses are subdivided by DNA & RNA viruses are subdivided by

capsid shape & whether they do or don't capsid shape & whether they do or don't have an envelopehave an envelope

Viral StructureViral Structure

DNA or RNA core surrounded by protein DNA or RNA core surrounded by protein sheath called capsidsheath called capsid

Nucleocapsid  includes the viral nucleic acid Nucleocapsid  includes the viral nucleic acid & its capsid& its capsid

Some form lipid rich covering around capsid Some form lipid rich covering around capsid called the envelopecalled the envelope

Envelope usually formed from host cell Envelope usually formed from host cell membranemembrane

Envelope may have spikes to help chemically Envelope may have spikes to help chemically recognize & attach to the host cellrecognize & attach to the host cell

Viral StructureViral Structure

TMV is helicalTMV is helical Adenovirus & polio Adenovirus & polio viruses are viruses are icosohedral (20 icosohedral (20 sided)sided)

Viral StructureViral Structure

T-phages have a head and a tailT-phages have a head and a tail

Bacteriophage or T-phageBacteriophage or T-phage

Among the most complex virusesAmong the most complex viruses Attack bacterial cellsAttack bacterial cells Composed of a icosohedral head, tail, Composed of a icosohedral head, tail,

base plate, & tail fibersbase plate, & tail fibers Long DNA molecule is inside the head Long DNA molecule is inside the head  Tail helps inject the viral DNA into host Tail helps inject the viral DNA into host

cellcell Tail fibers used to attach to hostTail fibers used to attach to host

RetrovirusRetrovirus

Contain RNAContain RNA Have an enzyme called Have an enzyme called

reverse transcriptase reverse transcriptase which helps use the which helps use the RNA to make DNARNA to make DNA

Use the host cell's Use the host cell's ribosomes & raw ribosomes & raw materials to make viral materials to make viral proteinsproteins

Cause some cancers & Cause some cancers & AIDSAIDS

HIV VirusHIV Virus

Lytic CycleLytic Cycle Phases of the Lytic Cycle of aPhases of the Lytic Cycle of a VirulentVirulent Virus:Virus:    Absorption:Absorption: Virus attaches itself to the cell. Virus attaches itself to the cell. Entry:Entry: Enzymes weaken the cell wall and nucleic acid is Enzymes weaken the cell wall and nucleic acid is

injected into the cell, leaving the empty caspid outside injected into the cell, leaving the empty caspid outside the cell. Many viruses actually enter the host cell intact.the cell. Many viruses actually enter the host cell intact.

Replication:Replication: Viral DNA takes control of cell activity. Viral DNA takes control of cell activity. Assembly:Assembly: All metabolic activity of the cell is directed to All metabolic activity of the cell is directed to

assemble new viruses.assemble new viruses. Release:Release: Enzymes disintegrate the cell in a process Enzymes disintegrate the cell in a process

called called lysislysis, releasing the new viral particles, releasing the new viral particles

Lytic CycleLytic Cycle

Source: http://science.howstuffworks.com/virus-human.htm

Lysogenic CycleLysogenic Cycle The Lysogenic Cycle of aThe Lysogenic Cycle of a TemperateTemperate Virus:Virus: The virus attaches itself and injects its DNA into the cell. The virus attaches itself and injects its DNA into the cell. The viral DNA attaches itself to the host DNA, becoming The viral DNA attaches itself to the host DNA, becoming

a new set of cell genes called a a new set of cell genes called a prophageprophage. . When the host cell divides, this new gene is replicated When the host cell divides, this new gene is replicated

and passed to new cells. This causes no harm to the and passed to new cells. This causes no harm to the cell, but may alter its traits. cell, but may alter its traits.

Now there are two possibilities: Now there are two possibilities: • The prophage survives as a permanent part of the DNA of the The prophage survives as a permanent part of the DNA of the

host organism. host organism. • Some external stimuli can cause the prophage to become active, Some external stimuli can cause the prophage to become active,

using the cell to produce new viruses. using the cell to produce new viruses.   

Lysogenic CycleLysogenic Cycle

Source: http://science.howstuffworks.com/virus-human.htm

Viral ControlViral Control Interferon are proteins made by cells to fight virusesInterferon are proteins made by cells to fight viruses Two types of viral vaccines exist --- inactivated & Two types of viral vaccines exist --- inactivated &

attenuatedattenuated Inactivated virus vaccines don't replicate in the Inactivated virus vaccines don't replicate in the

host's systemhost's system Attenuated viral vaccines have been genetically Attenuated viral vaccines have been genetically

altered so they can't cause diseasealtered so they can't cause disease Antiviral drugs (AZT, acyclovir, & azidothymidine) Antiviral drugs (AZT, acyclovir, & azidothymidine)

interfere with viral DNA synthesisinterfere with viral DNA synthesis Protease Inhibitors interfere with viral capsid Protease Inhibitors interfere with viral capsid

productionproduction New viruses emerge as rain forests are cleared New viruses emerge as rain forests are cleared

(Ebola virus)(Ebola virus)

Adenovirus

Common cold

Influenza Virus Note-plasma membrane

HIV

Coronavirus SARS

ClassificationClassification By Nucleic acidsBy Nucleic acids By StructureBy Structure By Speed of InfectionBy Speed of Infection By SpecificityBy Specificity

Classify By Nucleic Acid in CoreClassify By Nucleic Acid in CoreDNA VirusesDNA Viruses

DNA inserted into host cell is incorporated DNA inserted into host cell is incorporated into the host genome.into the host genome.

Host cell does not differentiate Host cell does not differentiate Viral DNA commandeers control and Viral DNA commandeers control and

signals host to replicate viral DNA and to signals host to replicate viral DNA and to produce viral protein.produce viral protein.

Host uses itself up to produce theseHost uses itself up to produce these Result is a hollow sack of viral particles.Result is a hollow sack of viral particles.

Classify By Nucleic Acid in CoreClassify By Nucleic Acid in CoreRNA VirusesRNA Viruses

RNA is inserted into the cell RNA is inserted into the cell Host cell is signaled to make viral Host cell is signaled to make viral

RNA and viral proteinRNA and viral protein Result is the same for host cellResult is the same for host cell

DEATHDEATH

Polio virus is a RNA virus

Classify By Nucleic Acid in CoreClassify By Nucleic Acid in CoreRetrovirus VirusesRetrovirus Viruses

Nucleic acid is RNA but with the Nucleic acid is RNA but with the addition of enzyme-Reverse addition of enzyme-Reverse TranscriptaseTranscriptase

Enzyme allows production of DNA from Enzyme allows production of DNA from viral RNAviral RNA

RNA->DNA->RNA->ProteinRNA->DNA->RNA->Protein Does this disprove the Does this disprove the Central DogmaCentral Dogma?? Lab use of reverse transcriptaseLab use of reverse transcriptase

HIV is a retrovirus

RNA

Reverse transcriptase

Classify By SpecificityClassify By Specificity

Viruses are extremely specific as to Viruses are extremely specific as to which kinds of cells they parasitizewhich kinds of cells they parasitize

Identify protein receptors on the Identify protein receptors on the outside of host cellsoutside of host cells

Tobacco mosaic virus does not infect Tobacco mosaic virus does not infect animals or bacteria.animals or bacteria.

The viral protein determines the The viral protein determines the specificityspecificity

Classify By SpeedClassify By Speed

Lytic viruses attack the host cell Lytic viruses attack the host cell quicklyquickly

Lysogenic or latent viruses insert the Lysogenic or latent viruses insert the nucleic acid and lie dormant.nucleic acid and lie dormant.

Unknown chemical signals activate Unknown chemical signals activate themthem

They may never be activatedThey may never be activated If host cell divides the viral genome is If host cell divides the viral genome is

replicated along with other DNAreplicated along with other DNA

MutationMutation Viral nucleic acids can mutateViral nucleic acids can mutate Sometimes pick up parts of host DNASometimes pick up parts of host DNA Sometimes pick up host membraneSometimes pick up host membrane Three types of pathogens that have Three types of pathogens that have

no vaccinesno vaccinesRetrovirusesRetrovirusesThose with multiple antigensThose with multiple antigensThose that mutate rapidlyThose that mutate rapidly

HIV is a retrovirus with many HIV is a retrovirus with many antigens that mutates rapidlyantigens that mutates rapidly..

Origin of VirusesOrigin of Viruses

Hypothesis 1. Viruses predate first Hypothesis 1. Viruses predate first cellscells

Hypothesis 2. Viruses are cellular Hypothesis 2. Viruses are cellular fragmentsfragments

Evidence for 2 is that some viruses Evidence for 2 is that some viruses wrap their DNA around histones to wrap their DNA around histones to form nucleosomes as eukaryotic cellsform nucleosomes as eukaryotic cells

Viruses have followed own Viruses have followed own evolutionary path.evolutionary path.

Viroids and Prions: The Ultimate in Simplicity

Plant Viroid

Prion

ViroidsViroids

Naked RNA found in plant cellsNaked RNA found in plant cells Infectious agentsInfectious agents Process of infection a mysteryProcess of infection a mystery As is replicationAs is replication May interfere with gene regulationMay interfere with gene regulation

PrionsPrions

Naked protein not associated with a Naked protein not associated with a nucleic acidnucleic acid

Infectious agentInfectious agent Action unknownAction unknown Identified as cause of Identified as cause of

scrapie--sheepscrapie--sheepmad cow--bovinemad cow--bovineC-J—humansC-J—humans

BacteriaBacteriaUnicellularUnicellular

ProkaryotesProkaryotesPoint of a straight pinwith thousands of

bacterial cells

HistoryHistory

LeeuwenhoekLeeuwenhoek• Probably first person to see bacteriaProbably first person to see bacteria

Louis PasteurLouis Pasteur• Father of bacteriologyFather of bacteriology• First person to study bacteria First person to study bacteria

extensivelyextensively Robert PetriRobert Petri

• Developed the petri dishDeveloped the petri dish Used to culture bacteriaUsed to culture bacteria

Koch’s PostulatesKoch’s Postulates

A formalized group of criteria for A formalized group of criteria for establishing the cause of an establishing the cause of an infectious diseaseinfectious disease

The microorganism must be present The microorganism must be present in every case of a disease.in every case of a disease.

The organism must be grown in pure The organism must be grown in pure culture from diseased hosts.culture from diseased hosts.

Koch’s Postulates continuedKoch’s Postulates continued

The same disease must be produced The same disease must be produced when a pure culture of the organism when a pure culture of the organism is introduced into susceptible hosts.is introduced into susceptible hosts.

The organism must be recovered The organism must be recovered from the experimentally infected from the experimentally infected host.host.

Koch’s bacterial discoveryKoch’s bacterial discovery

18761876 Convincing proof of “germ theory” of Convincing proof of “germ theory” of

diseasedisease Showed that Showed that Bacillus anthracisBacillus anthracis is is

cause of cause of anthraxanthrax• Often fatal disease in humans, sheep Often fatal disease in humans, sheep

and other animalsand other animals

Koch’s procedureKoch’s procedure

Under microscope, observed Under microscope, observed B. anthracisB. anthracis cells in blood and spleen of dead sheepcells in blood and spleen of dead sheep

Inoculated mice with the infected sheep Inoculated mice with the infected sheep bloodblood

Recovered Recovered B. anthracisB. anthracis from blood of mice from blood of mice Grew bacteria in pure culture and showed Grew bacteria in pure culture and showed

that they caused anthrax when injected that they caused anthrax when injected into healthy mice.into healthy mice.

From this and later work with From this and later work with Mycobacterium tuberculosisMycobacterium tuberculosis, Koch’s , Koch’s Postulates formalizedPostulates formalized

Types of ImmunityTypes of Immunity Naturally acquired passiveNaturally acquired passive

• From mother at birthFrom mother at birth• TemporaryTemporary

Naturally acquired passiveNaturally acquired passive• Recover from diseaseRecover from disease• Make antibodiesMake antibodies• Permanent in most casesPermanent in most cases

Artificially acquired passiveArtificially acquired passive• From a serumFrom a serum• Some other animal makes the antibodiesSome other animal makes the antibodies• Requires booster shotRequires booster shot• Example tetanusExample tetanus

Artificially acquired activeArtificially acquired active• From vaccineFrom vaccine• You make the antibodiesYou make the antibodies• Contains dead or weakened pathogensContains dead or weakened pathogens

ReferencesReferences

http://spa.k12.ar.us/massengale/viruhttp://spa.k12.ar.us/massengale/virus_notes_b1.htms_notes_b1.htm