Ch 9, Sec 1 Viruses Virus - tiny, nonliving particle that invades, multiplies inside a living cell - not a cell - do not have characteristics of organisms - can only multiply when inside a living cell - no organisms are safe from viruses *The only way in which viruses are like organisms is that they can multiply

Host - a living thing that provides a source of energy for a virus or an organism Parasite - organisms that live on or in a host and cause harm Almost all viruses destroy their host cells Structure of the Virus - smaller than cells, vary in size & shape - * two basic parts - protein coat that protects virus - inner core with genetic material (instructions for making new viruses)

- viruses have unique protein shapes on outer surface - protein shape allows virus to attach to certain cells (like a lock & key) - ex: most cold viruses infect cells only in nose & throat of humans - Bacteriophage (bacteria eater) - virus that infects bacteria

How viruses multiply - *Once inside cell, genteic material takes over the cell’s functions, insturcting cell to produce the virus’s proteins and genetic material. The proteins and genetic material assemble into new viruses - some viruses take over immediately, others wait - Active Viruses - once virus enters cell, it immediately takes over cell’s functions, making the cell produce the virus’s proteins & genetic material, making new virus’s

- Hidden Viruses - some virus’s stay inactive in the host cell, being copied into the new host cells - under the right conditions, the virus becomes active, taking over host cell’s functions, creating new little viruses inside the cell, then the host cell bursts, releasing the viruses - ex: cold sore virus, hides in nerve cells

Viruses & Disease (viruses cause diseases) - some viruses have a short disease duration, others can cause deadly diseases (ex: HIV causes AIDS) - Spread of viral disease - through contact with contaminated object, or bite of infected animal (rabies, distemper) - cold & flu viruses spread through sneezes or coughs in air - other viruses spread through contact with body fluids, blood

- Treating Viral Diseases - no cures for viral diseases - over the counter meds can relieve symptoms of viral infection - * rest, lots of fluids, eating properly, best way to recover from viral disease - Preventing Viral Diseases - Vaccine - substance introduced into body to stimulate production of chemicals that destroy specific disease-causing viruses or organisms

- weakened or altered virus, does not cause disease, but triggers body’s natural defense, and body will remember the virus and attack before it has ability to cause harm - other way to prevent viral disease - staying healthy and adequate rest & exercise