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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