Viruses: Living or Not

Viruses:Viruses:Living or NotLiving or Not

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VirusesViruses Virus – Latin for “poison”Virus – Latin for “poison” Russian Biologist Dmitri Ivanovski Russian Biologist Dmitri Ivanovski

(1892) – Tobacco Mosaic Disease…(1892) – Tobacco Mosaic Disease…not determined to be a virus until not determined to be a virus until 1930…known as the first virus to be 1930…known as the first virus to be discovered!~discovered!~

Characteristics of Characteristics of VirusesViruses

Scientist that studies viruses is called a Scientist that studies viruses is called a virologist!virologist!

Among the Among the smallest smallest biological biological particlesparticles (not cells) (not cells) that are capable of that are capable of causing harm in causing harm in living organisms. living organisms.

Virus particles are Virus particles are called called virionsvirions

5000 influenza 5000 influenza viruses can fit viruses can fit inside the head of a inside the head of a pin!pin!

Studying the “T4-Studying the “T4-BacteriophageBacteriophage

Also known as:Also known as: “eaters of bacteria” “eaters of bacteria” have a head and tail region – (serve have a head and tail region – (serve as the principle experimental object as the principle experimental object in studying viruses)in studying viruses)

Why study it?

VIRUSES & CELLSVIRUSES & CELLSCharacteristicCharacteristic VIRUSVIRUS CELLCELL

StructureStructure DNA or RNA core, DNA or RNA core, capsidcapsid

ReproductionReproduction Only within a hostOnly within a host

Genetic CodeGenetic Code DNA or RNADNA or RNA

Growth/DvpmtGrowth/Dvpmt NoNo

EnergyEnergy NoNo

Response to Response to EnvironmentEnvironment

NoNo

Change over timeChange over time YesYes

Not Considered LivingNot Considered Living

A virus is A virus is notnot a a bacteria, fungus, bacteria, fungus, protist, plant or protist, plant or animal.animal.

They They do not carry do not carry out cellular out cellular functionsfunctions..

They They do not grow do not grow or undergo or undergo divisiondivision

Not Considered LivingNot Considered Living

Viruses Viruses cannot cannot replicate on their replicate on their ownown – they need to – they need to infect a infect a HOSTHOST and and use the hosts use the hosts organelles and organelles and enzymes to do this!enzymes to do this!

Obligate intracellular Obligate intracellular parasitesparasites

Viral DiseaseViral Disease

Viral infections generally behave Viral infections generally behave in 2 ways:in 2 ways:

1. Viruses reproduce and cause 1. Viruses reproduce and cause disease immediately (disease immediately (lytic or activelytic or active))

2. Viruses integrate into the host cell 2. Viruses integrate into the host cell ((lysogenic or dormant)lysogenic or dormant)

Viral Replication – Lytic Viral Replication – Lytic Cycle InfectionCycle Infection

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LYSOGENIC CYCLE

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Quick Review….Quick Review….

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What Organisms and Host What Organisms and Host Cells Do Viruses Infect?Cells Do Viruses Infect?

Infection by virusesInfection by viruses viruses infect bacteria, plants, animals and other viruses infect bacteria, plants, animals and other

living organisms in order to reproduceliving organisms in order to reproduce a given virus usually infects a limited number of a given virus usually infects a limited number of

species.species. within a host organism, usually only a limited within a host organism, usually only a limited

number of cell types are susceptible to infection by a number of cell types are susceptible to infection by a given virusgiven virus

Host rangeHost range array of host cells that a particular virus can infect array of host cells that a particular virus can infect determined by a “lock-and-key” fit between the virus determined by a “lock-and-key” fit between the virus

and a receptor on the surface of a host celland a receptor on the surface of a host cell Ex: one type of herpes virus causes cold sore, a Ex: one type of herpes virus causes cold sore, a

different one causes genital sores!different one causes genital sores!

Virus StructureVirus Structure

Nucleic acid

Envelope

Capsid

How are Viruses How are Viruses Classified?Classified?

Genetic MaterialGenetic Material DNA orDNA or RNA (retrovirus/mutates RNA (retrovirus/mutates

frequently)frequently) But not bothBut not both

Capsid (Protein) Capsid (Protein) Structure = 95% of virusStructure = 95% of virus Helical (rod shaped)Helical (rod shaped) Polyhedral (spherical)Polyhedral (spherical) ComplexComplex

Presence or absencePresence or absence of a of a membranousmembranous envelope envelope surrounding the capsidsurrounding the capsid

**No envelope = naked virus**No envelope = naked virus

Helical Marburg virus

Polyhedral SV40 virus

Complex bacteriophage

•HIV, for example, only will enter cells that have a surface protein molecule called CD4.

•CD4 are only found on white blood cells.

•Sometimes, a virus can mutate and change its host range.

•Avian flu virus (influenza A/H5N1) – at first only birds, then humans•Swine flu (influenza A/H1N1) – pigs to humans.

• The change in host range of a virus can be one factor in the emergence of a new disease.

Host RangeHost Range

What Diseases are Caused What Diseases are Caused by Viruses?by Viruses?

Infectious diseasesInfectious diseases RNA virusesRNA viruses (retroviruses) (retroviruses) DNA virusesDNA viruses

AIDSAIDS Respiratory DiseaseRespiratory Disease

Influenza (flu) Influenza (flu) SmallpoxSmallpox

Common coldCommon cold ChickenpoxChickenpox

PolioPolio MononucleosisMononucleosis

MeaslesMeasles Cold SoresCold Sores

Tumor Viruses – cause Cancer ex: HPVTumor Viruses – cause Cancer ex: HPV OncovirusesOncoviruses

How Can Viral Diseases Be How Can Viral Diseases Be Prevented and Treated?Prevented and Treated?

Good hygieneGood hygiene Avoid contact with contaminated food, water, fecal Avoid contact with contaminated food, water, fecal

material or body fluids.material or body fluids. Wash hands frequently.Wash hands frequently.

VaccinesVaccines Stimulate natural defenses with in the body.Stimulate natural defenses with in the body. Contain a component of or a weakened or killed virus Contain a component of or a weakened or killed virus

particles.particles. Are developed for many once common illnesses such as Are developed for many once common illnesses such as

smallpox, polio, mumps, chicken pox.smallpox, polio, mumps, chicken pox. Not available for all viruses.Not available for all viruses.

Anti-viral drugs (but not antibiotics)Anti-viral drugs (but not antibiotics) Available for only a few viruses.Available for only a few viruses. Inhibit some virus development and/or relieve symptoms.Inhibit some virus development and/or relieve symptoms.

How Do New Viruses How Do New Viruses Emerge?Emerge?

Through mutation and evolution of genetic Through mutation and evolution of genetic code…changes to the protein coat code…changes to the protein coat therefore changing the “lock and key” fit! therefore changing the “lock and key” fit! And no longer recognizable to a host’s And no longer recognizable to a host’s immune system!immune system!

Human population expanding into Human population expanding into previously uninhabited areas (increased previously uninhabited areas (increased contact between humans and animals)contact between humans and animals)

Through the detection of previously Through the detection of previously unrecognized virusesunrecognized viruses

HSV1 vs HSV2

Human Papilloma Virus – Human Papilloma Virus – 14yo boy14yo boy

Polio VirusPolio Virus

Six countries (Afghanistan, Egypt, India, Niger, Nigeria, and Pakistan) still have polio circulating

VIRUS MINI QUIZVIRUS MINI QUIZ

1.1. THE PRIMARY FUNCTION THE PRIMARY FUNCTION OF ALL VIRUSES IS TO OF ALL VIRUSES IS TO REPLICATE!!REPLICATE!!

MINI QUIZ…MINI QUIZ…

2. 2. WHAT IS THE WHAT IS THE TYPICAL/COMMON VIRUS TYPICAL/COMMON VIRUS THAT STUDENTS STUDY THAT STUDENTS STUDY WHEN LEARNING ABOUT WHEN LEARNING ABOUT VIRUSES?VIRUSES?

T4 BacteriophageT4 Bacteriophage


3. IN ORDER FOR A VIRUS TO 3. IN ORDER FOR A VIRUS TO REPLICATE IT NEEDS TO BE REPLICATE IT NEEDS TO BE IN A IN A HOSTHOST CELL CELL


4. VIRAL REPRODUCTION 4. VIRAL REPRODUCTION THAT KILLS THE HOST CELL THAT KILLS THE HOST CELL IS CALLED THE IS CALLED THE LyticLytic CYCLE! CYCLE!


5. WHEN VIRAL DNA IS 5. WHEN VIRAL DNA IS EMBEDDED INTO A HOST EMBEDDED INTO A HOST CELL’S DNA IT FORMS A CELL’S DNA IT FORMS A PROPHAGEPROPHAGE


6. ANOTHER NAME FOR 6. ANOTHER NAME FOR INFLUENZA IS INFLUENZA IS FLU VIRUSFLU VIRUS


7. 3 WAYS VIRUSES CAN BE 7. 3 WAYS VIRUSES CAN BE TREATED/PREVENTED TREATED/PREVENTED ARE….ARE….

1.1. HygieneHygiene

2.2. VaccinesVaccines

3.3. AntiViralsAntiVirals


8. SCIENTISTS THAT STUDY 8. SCIENTISTS THAT STUDY VIRUSES ARE CALLED VIRUSES ARE CALLED VIROLOGISTSVIROLOGISTS


9.9. 3 WAYS THAT VIRUSES CAN 3 WAYS THAT VIRUSES CAN BE TRANSMITTED ARE….BE TRANSMITTED ARE….

-- droplets in the air (e.g. cold, flu, tuberculosis)-- via food or water (e.g. Salmonella, food

poisoning)-- via mosquitoes, ticks (e.g. malaria, West Nile

virus, Lyme disease)-- physical contact (e.g. pinkeye, herpes,

chickenpox, sexually transmitted diseases)


10. A VIRUS THAT HAS ONLY A 10. A VIRUS THAT HAS ONLY A CAPSIDCAPSID SURROUNDING IT’S SURROUNDING IT’S GENETIC INFORMATION AND GENETIC INFORMATION AND NO NO ENVELOPEENVELOPE IS CALLED A IS CALLED A NAKEDNAKED VIRUS.VIRUS.

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Viruses: Living or Not