KEY CONCEPTKEY CONCEPT Infections can be caused Infections can be caused

in several ways.in several ways.

California Content StandardsCalifornia Content Standards 10. Organisms have a variety of mechanisms to combat 10. Organisms have a variety of mechanisms to combat

disease. As a basis for understanding the human immune disease. As a basis for understanding the human immune response: response:

c. c. Students know Students know how how vaccinationvaccination protects an individual from protects an individual from infectious diseases.infectious diseases.

d. d. Students know Students know there are important there are important differences between differences between bacteriabacteria and and virusesviruses with respect to their requirements for with respect to their requirements for growth and replication, the body's primary defenses against growth and replication, the body's primary defenses against bacterial and viral infections, and effective treatments of these bacterial and viral infections, and effective treatments of these infections. infections.

What are some examples of viruses?What are some examples of viruses?

Class List:Class List:

A virus is a type of parasite—it depends on a host organism for survival and reproduction

Viruses & Bacteria:Viruses & Bacteria: both cause infectionboth cause infection

PathogenPathogen: any disease-causing agent : any disease-causing agent Prevent pathogens with vaccinesPrevent pathogens with vaccines Viruses are much smaller than bacteriaViruses are much smaller than bacteria

viruses50-200 nm

prokaryotics cells200-10,000 nm

prion2-10 nm

viroids5-150 nm

eukaryotics cells10,000-100,000 nm

100 nm1 nanometer (nm) = one

billionth of a meter

Virus : Infectious particle made of:Virus : Infectious particle made of:- only a strand of DNA or RNA- only a strand of DNA or RNA-a protein coat.-a protein coat.

They aren’t living!They aren’t living!Can’t reproduce on their ownCan’t reproduce on their ownNot made up of cellsNot made up of cellsDo Respond to environmentDo Respond to environmentCan prevent with vaccineCan prevent with vaccine

Bacteria: Living single cellCan reproduce on its ownCan be killed with antibioticsHave DNA and respond to environmentCan prevent with vaccine and kill with antibiotics

•Bacteriophages infect bacteria.

colored SEM; magnifications:large photo 25,000; inset 38,000x

Capsid – protein shell surrounding the viruses Capsid – protein shell surrounding the viruses DNADNADNA – genetic material that allows the virus to DNA – genetic material that allows the virus to reproducereproduceTail Sheath: attaches tail fibers to capsidTail Sheath: attaches tail fibers to capsidTail Fibers – allow the virus to attach to a cellTail Fibers – allow the virus to attach to a cell

At your table work together to make a double bubble for Viruses and Bacteria

How are viruses classified?How are viruses classified?

They are classified by:They are classified by:1.1. ShapeShape

2.2. Nucleic acid they contain (DNA or RNA)Nucleic acid they contain (DNA or RNA)

3.3. The kind of organism they infectThe kind of organism they infect

Viruses differ in shape and in ways Viruses differ in shape and in ways of entering host cells. of entering host cells.

Viruses have a simple structure. Viruses have a simple structure. genetic material genetic material capsid, a protein shell capsid, a protein shell maybe a lipid envelope, a protective outer coat maybe a lipid envelope, a protective outer coat

capsid nucleic acid

lipidenvelope

surfaceproteins

capsid

nucleic acid

lipid envelope

Surface proteins capsidsurfaceproteins

nucleic acid

helical(rabies)

polyhedral(foot-and-mouth

disease)

enveloped(influenza)

host bacterium

The bacterophage attachesand injects it DNA into a host bacterium.

The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells.

The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages.

The viral DNA forms a circle.

Viruses cause two types of Viruses cause two types of infections. infections.

A lytic infection causes the host cell to burst. A lytic infection causes the host cell to burst.

The virus may enter thelysogenic cycle, in which thehost cell is not destroyed.

A lysogenic infection does no immediate harm. A lysogenic infection does no immediate harm.

The viral DNA is called a prophagewhen it combines withthe host cell’s DNA.

Although the prophage is notactive, it replicates along withthe host cell’s DNA.

Many cell divisions produce acolony of bacteria infectedwith prophage.

The prophage may leave thehost’s DNA and enter thelytic cycle.

House Guest AnalogyHouse Guest Analogy On the same double bubble paper think of a On the same double bubble paper think of a

virus as an unwanted house guest.virus as an unwanted house guest. Write a few sentence pretending a lytic virus is Write a few sentence pretending a lytic virus is

a house guest.a house guest. Now write what a lysogenic virus would be Now write what a lysogenic virus would be

like as a house guest.like as a house guest. To Refresh your memories:To Refresh your memories:

A lytic infection causes the host cell to burst.A lytic infection causes the host cell to burst. A lysogenic infection does no immediate harm.A lysogenic infection does no immediate harm.

Viruses cause many infectious Viruses cause many infectious diseases diseases

There are many examples of viral infections.There are many examples of viral infections.

Chicken PoxChicken PoxHepatitis AHepatitis ARabiesRabiesWest NileWest NileBird FluBird FluInfluenzaInfluenzaCommon ColdCommon ColdSARSSARSHIVHIVSwine FluSwine Flu

Vaccines are made from Vaccines are made from weakened pathogens. weakened pathogens.

A vaccine stimulates the body’s own immune A vaccine stimulates the body’s own immune response. response.

Vaccines prepare the immune system for a Vaccines prepare the immune system for a future attack.future attack.

Vaccines are the only way to control the spread Vaccines are the only way to control the spread of viral disease.of viral disease.

Animal Models: General Method

A blood test reveals the levels of viruses, T-cells and antibodies.

A “challenge” is given: a highly virulent strain of the virus is injected.

Genetic and biochemical analysis can reveal why vaccine failed.

If the animal is healthy for a “long time,” then human trials can begin.

If the animal becomes sick or dies, more blood tests are taken.

If the reason for vaccine failure is discovered, a new round of design is initiated OR the project ends.

Vaccine or no VaccineVaccine or no Vaccine

VaccineVaccine Chicken PoxChicken Pox Hepatitis AHepatitis A MumpsMumps RabiesRabies HPVHPV FluFlu

No VaccineNo Vaccine West NileWest Nile SARSSARS Common ColdCommon Cold Bird FluBird Flu HIVHIV