Download - Viruses
18.2 Viral Structure and Reproduction
– Simple and small pathogen– Made of Capsid and RNA or DNA
– Non living (must infect living cells)
18.2 Viral Structure and Reproduction
Shapes
capsid nucleic acid
lipidenvelope
surfaceproteins
capsid
nucleic acid
lipid envelope
Surface proteins
capsidsurfaceproteins
nucleic acid(rabies)
(foot-and-mouthdisease)
(influenza)
1. Enveloped
2. Helical
3. Polyhedral
18.2 Viral Structure and Reproduction
4. Bacteriophages- viruses that infect bacteria.
capsid
DNA
tail sheath
tail fiber
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
18.2 Viral Structure and Reproduction
- viruses of eukaryotes enter by endocytosis and also fuse with membrane
18.2 Viral Structure and Reproduction
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 infections.
• A lytic infection causes the host cell to burst.
The virus may enter thelysogenic cycle, in which thehost cell is not destroyed.
18.2 Viral Structure and Reproduction
• 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.
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