KEY CONCEPT Infections can be caused in several ways.

California Content Standards 10. Organisms have a variety of mechanisms to combat disease. As a basis for understanding the human immune response: 10. Organisms have a variety of mechanisms to combat disease. As a basis for understanding the human immune response: c. Students know how vaccination protects an individual from infectious diseases. d. Students know there are important differences between bacteria and viruses with respect to their requirements for growth and replication, the body's primary defenses against bacterial and viral infections, and effective treatments of these infections.

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: both cause infection Pathogen: any disease-causing agent Pathogen: any disease-causing agent Prevent pathogens with vaccines Prevent pathogens with vaccines Viruses are much smaller than bacteria Viruses are much smaller than bacteria viruses nm prokaryotics cells ,000 nm prion 2-10 nm viroids nm eukaryotics cells 10, ,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter

Virus : Infectious particle made of: - only a strand of DNA or RNA -a protein coat. They aren’t living! Can’t reproduce on their own Not made up of cells Do Respond to environment Can prevent with vaccine Bacteria: Living single cell Can reproduce on its own Can be killed with antibiotics Have DNA and respond to environment Can 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 DNA DNA – genetic material that allows the virus to reproduce Tail Sheath: attaches tail fibers to capsid Tail 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? They are classified by: 1. Shape 2. Nucleic acid they contain (DNA or RNA) 3. The kind of organism they infect

Viruses differ in shape and in ways 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 lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid helical (rabies) polyhedral (foot-and-mouth disease) enveloped (influenza)

host bacterium The bacterophage attaches and injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA directs the host cell to produce new viral parts. The parts assemble into new bacteriophages. The viral DNA forms a circle. Viruses cause two types of infections. A lytic infection causes the host cell to burst. A lytic infection causes the host cell to burst. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

A lysogenic infection does no immediate harm. A lysogenic infection does no immediate harm. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. The prophage may leave the host’s DNA and enter the lytic cycle.

House Guest Analogy On the same double bubble paper think of a virus as an unwanted house guest. On the same double bubble paper think of a virus as an unwanted house guest. Write a few sentence pretending a lytic virus is a house guest. Write a few sentence pretending a lytic virus is a house guest. Now write what a lysogenic virus would be like as a house guest. Now write what a lysogenic virus would be 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 diseases There are many examples of viral infections. There are many examples of viral infections. Chicken Pox Hepatitis A Rabies West Nile Bird Flu Influenza Common Cold SARSHIV Swine Flu

Vaccines are made from weakened pathogens. A vaccine stimulates the body’s own immune response. A vaccine stimulates the body’s own immune response. Vaccines prepare the immune system for a future attack. Vaccines prepare the immune system for a future attack. Vaccines are the only way to control the spread of viral disease. Vaccines are the only way to control the spread of viral disease.

Vaccine or no Vaccine Vaccine Vaccine Chicken Pox Chicken Pox Hepatitis A Hepatitis A Mumps Mumps Rabies Rabies HPV HPV Flu Flu No Vaccine No Vaccine West Nile SARS Common Cold Bird Flu HIV