VIRUSESVIRUSES

What is a Virus?What is a Virus?

Made up of Made up of DNA or RNADNA or RNA surrounded by a surrounded by a protein coatprotein coat

Cause disease and infectionCause disease and infectionNot living (no growth, development or Not living (no growth, development or

respiration)respiration)Need a host cell to Need a host cell to replicatereplicate (make (make

copies), copies),

Virus StructureVirus Structure

Different shapes and sizes but all have:Different shapes and sizes but all have:1. 1. RNA or DNARNA or DNA in core in core2. protein coat around nucleic acid called 2. protein coat around nucleic acid called

capsidcapsid3. Some have 3. Some have envelopeenvelope – acts like a disguise – acts like a disguise

in host.in host.

Many viruses are host specific! Many viruses are host specific! Ex. Small pox infects only humansEx. Small pox infects only humans

Other viruses infect many species.Other viruses infect many species.Ex. Flu infects humans and other animals Ex. Flu infects humans and other animals

(pigs, birds)(pigs, birds)

How do viruses replicate?How do viruses replicate?

Lytic vs Lysogenic CyclesLytic vs Lysogenic Cycles

Lytic CycleLytic Cycle1.1. Attachment Attachment - virus attaches to host cell - virus attaches to host cell2. 2. EntryEntry - virus injects its DNA or RNA into - virus injects its DNA or RNA into

host cellhost cell3. 3. ReplicationReplication – viral parts are made using – viral parts are made using

genetic code of virus and raw materials of genetic code of virus and raw materials of hosthost

4. 4. AssemblyAssembly – virus particles are – virus particles are assembledassembled

5. 5. Lysis and releaseLysis and release – host cell bursts – host cell bursts releasing new virus particlesreleasing new virus particlesEx. Bacteriophage virus infecting bacteria host cellEx. Bacteriophage virus infecting bacteria host cell

Lytic CycleLytic Cycle

Lytic Virus Characteristics Lytic Virus Characteristics and Examplesand Examples

Infect host cell and start replicating Infect host cell and start replicating immediately (cycle takes ~30 immediately (cycle takes ~30 minutes and creates 200 new minutes and creates 200 new viruses!)viruses!)

cause disease symptoms within cause disease symptoms within daysdays

Small Pox, Measles, Polio, Cold Small Pox, Measles, Polio, Cold virus, Seasonal Influenzavirus, Seasonal Influenza

Small poxSmall pox

MeaslesMeasles

PolioPolio

Lysogenic CycleLysogenic Cycle

1. 1. AttachementAttachement2. 2. EntryEntry3. 3. Provirus formationProvirus formation – virus DNA is – virus DNA is

incorporated into host DNAincorporated into host DNA4. 4. Host Cell divisionHost Cell division – host cell copies all – host cell copies all

DNA including viral DNA, then dividesDNA including viral DNA, then divides5. 5. Provirus activationProvirus activation – provirus removes – provirus removes

itself from host DNA itself from host DNA 6. Lytic cycle begins6. Lytic cycle begins

Lysogenic CycleLysogenic Cycle

Lysogenic Virus Characteristics Lysogenic Virus Characteristics and Examplesand Examples

Provirus enters host cell and remains Provirus enters host cell and remains

inactive usually months to yearsinactive usually months to years Examples: Examples:

HepatitisHepatitisHerpesHerpes

Picture of hep b virus w/ large Picture of hep b virus w/ large viral protein filiments secreted viral protein filiments secreted by infected cellby infected cell

Herpes symplex 1 virusHerpes symplex 1 virus

Plant virusesPlant virusesTobacco mosaic virusTobacco mosaic virus

RNA virusRNA virusFirst virus identifiedFirst virus identified

Tomato Plant Virus Tomato Plant Virus RNA virusRNA virus

Retro VirusesRetro Viruses

viruses with viruses with RNARNAWhen injected into host cell, they must When injected into host cell, they must

inject enzyme called inject enzyme called reverse reverse transcriptasetranscriptase to make DNA to make DNA

Ex. HIVEx. HIV

Other Virus factsOther Virus facts

Some viruses are Some viruses are linked to cancerlinked to cancerEx. Hepatitis B – liver cancerEx. Hepatitis B – liver cancerEx. Human Papillomavirus (HPV) – cervical Ex. Human Papillomavirus (HPV) – cervical

cancercancer

PrionsPrions – similar to virus, but only – similar to virus, but only have protein (no nucleic acids)have protein (no nucleic acids)Ex. Mad Cow Disease caused by prionEx. Mad Cow Disease caused by prion

ViroidsViroids – similar to virus, but only – similar to virus, but only have RNAhave RNACause many plant infections Cause many plant infections

Mad Cow Disease in HumansMad Cow Disease in Humans

Emerging viruses Emerging viruses viruses that viruses that maymay have opportunity to have opportunity to reach epidemic proportions due to reach epidemic proportions due to

human encroachmenthuman encroachmenteBola (left) – causes hemorrhagic eBola (left) – causes hemorrhagic

feverfeverHanta virus (right) –causes Hanta virus (right) –causes

respiratory failurerespiratory failureDeer mouse (bottom) – carrier of Deer mouse (bottom) – carrier of

hanta virushanta virus

EbolaEbola

Which came first?Which came first?Viruses or cellsViruses or cells

Which came first?Which came first?Viruses or cellsViruses or cells

Scientists believe the Scientists believe the host cellshost cells evolved evolved firstfirst..

Viruses Viruses needneed host cells to replicate host cells to replicate