1. 18.2 Viral Structure and Reproduction Viruses exist in a variety of shapes and sizes.

2. 18.2 Viral Structure and Reproduction –Simple and small pathogen –Made of Capsid and RNA or DNA –Non living (must infect living cells)

3. 18.2 Viral Structure and Reproduction Shapes capsid nucleic acid lipid envelope surface proteins capsid nucleic acid lipid envelope Surface proteins capsid surface proteins nucleic acid (rabies) (foot-and-mouth disease) (influenza) 1. Enveloped 2. Helical 3. Polyhedral

4. 18.2 Viral Structure and Reproduction 4. Bacteriophages- viruses that infect bacteria. capsid DNA tail sheath tail fiber

5. 18.2 Viral Structure and Reproduction Viruses enter cells in various ways. colored SEM; magnifications: large photo 25,000; inset 38,000x –bacteriophages pierce host cells

6. 18.2 Viral Structure and Reproduction - viruses of eukaryotes enter by endocytosis and also fuse with membrane

7. 18.2 Viral Structure and Reproduction 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. The virus may enter the lysogenic cycle, in which the host cell is not destroyed.

8. 18.2 Viral Structure and Reproduction 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.

9. 18.2 Viral Structure and Reproduction Viral Diseases Common Cold – contaminated objects Influenza – respiratory droplets (sneeze) HIV/AIDS – body fluids Chicken Pox – respiratory droplets (sneeze) Hepatitis B – contaminated blood/ body fluids West Nile Virus - mosquitoes HPV – sexual contact (causes cancer) Small Pox – respiratory droplets Mumps – respiratory droplets Measles – respiratory droplets Food Poisoning – eating bad food

10. 18.2 Viral Structure and Reproduction Virus Prevention Vaccines Wash hands/ Good hygiene Cough/ Sneeze in tissue/ sleeve Disinfectants (breaks apart capsid/RNA)