1. Viruses Introduction AAAA virus is a tiny nonliving particle that enters and then reproduces inside a living cell. SSSSome of the organisms Viruses infect include: 1. Humans 2. Plants 3. Animals 4. Bacteria WWWWhat do you call a Virus that infects bacteria? Bacteriophage w w w which means “bacteria eater”

2. WWWWhat is an Infection? When bacteria or viruses cause a disease or an illness TTTThe virus is called a parasite. Parasite can only live in a host WWWWhat is a host? An organism that provides energy and a suitable environment/home for a parasite

3. How big are they? WWWWhat size is the bacterium ? 750nm WWWWhat size is the Red Blood Cell? 7,500nm WWWWhat size is the influenza virus? 90nm

4. The Structure of Viruses All viruses have two basic parts 1. A protein coat that protects the virus called Capsid 2. An inner core made of genetic material DNA or RNA SSSSome viruses are surrounded by an Membrane envelope.

5. DNA and RNA viruses TTTT4 bacteriophage is a DNA virus MMMMagnification: x55,065 SSSSome viruses have RNA instead of DNA HHHHIV i i i is type of RNA virus

6. How do viruses attach to a Host cell? VVVViruses have outer membrane proteins TTTThe host cell membrane also has proteins on it TTTThe host and the virus surface proteins fit together like a “LOCK AND KEY” IIIIf these do not fit together the virus will not be able to attach to the host cell and infect it !

7. Bacteriophage VVVVirus that infects only bacteria TTTThe DNA is inside the head TTTThe head is made of special protein coat called:CAPSID TTTThe tail contracts and pushes the DNA inside the bacteria TTTThe fibers have special Binding proteins that attach to bacterial cell wall

8. Bacteriophage  The head passes its DNA down the tail and into the host (bacteria)  Within 25 minutes the dying bacteria is teeming with about 100 fresh copies of the virus  Viruses use the bacteria’s machinery such as the Ribosomes to make proteins needed to assemble new viruses

9. How Active Viruses Multiply ACTIVE VIRUSES enter cells and immediately begin to multiply, which may lead to the quick death of the invaded cells. Active viruses cause ACUTE INFECTION which only last few days

10. How Active Viruses Multiply Virus attaches to the surface of a living cell. Virus injects genetic material into cell. Cell produces viral proteins and genetic material. Viruses assemble. Cell bursts, releasing viruses.

11. How Hidden Viruses Multiply HIDDEN VIRUSES “hide” inside host cell before becoming active. Hidden viruses cause CHRONIC INFECTION which can last a lifetime

12. How Hidden Viruses Multiply Virus attaches to cell. Virus injects its genetic material. Virus’s genetic material becomes part of cell’s genetic material. Cell produces viral proteins and genetic material. Viruses are assembled Cell bursts, releasing viruses.

13. Review Questions Question: What kind of organisms do viruses infect? Answer: Humans Animals Bacteria Plants Question: Explain the difference between a host and a parasite Answer: * Host is the infected organism, provides suitable home for the parasite * Parasite needs a host to live Question: What is the name of a virus that infects only Bacteria? Answer: A Bacteriophage or T4 phage Question: Name the basic parts of a virus Answer: * Protein coat called “Capsid” * DNA or RNA * Some viruses have an “outer membrane”

14. Question: What type of genetic material is inside a virus? Answer: Either DNA or RNA but not both Question: Briefly describe what is an “Active Virus” ? Answer: * Active virus infects a host and multiplies immediately * Causes “Acute Infection” * Causes “Acute Infection” * Example: the Flu * Example: the Flu Question: Briefly describe what is a “Hidden Virus”? Answer: * Infects a host but doesn’t multiply immediately * Causes “Chronic Infection” * Causes “Chronic Infection” * May last a lifetime * May last a lifetime * Example: The HIV that causes AIDS * Example: The HIV that causes AIDS Herpes Epstein-Barr Herpes Epstein-Barr Question: How do viruses attach to a host cell? Answer: Both the host and virus have special proteins that fit together like a “Lock and Key” together like a “Lock and Key”