Download Viruses - Killeen ISD

Viruses 10-6
Are they alive?
What is a Virus?
• Structure that contains genetic material
(DNA or RNA) wrapped in protein (capsid)
• Does NOT have a cell
• Does NOT breathe, eat, produce wastes
• Can reproduce, but only if in a host cell
Types of Viruses
Structure of a Virus
How do viruses invade cells?
• Virus attaches to host
cell’s membrane
– is very specific to
certain cells
– Ex: cold virus can only
attach to respiratory
cells
• Virus shoots or injects
its DNA into the host
cell
Virus Lytic Cycle
How do viruses replicate?
• Lytic Cycle
– Virus DNA takes over cell immediately
– New virus parts are made
– Host cell bursts releasing new viruses to
infect nearby cells
– Has a short “incubation time”
– Ex: flu, cold, measles
Lytic Cycle
How do viruses replicate?
• Lysogenic Cycle
– Viral DNA “hides out” within host’s DNA
– Virus DNA gets copied everytime host cells copy
– At some point, virus goes into lytic cycle and kills
host cells
– Has long incubation time (months-years)
– Ex: HIV, warts, shingles, herpes
Lysogenic Cycle
Viral Reproduction
HIV Life Cycle
HIV attacks the
very system in our
bodies that we use
to fight infections.
*destroys/inhibit
T cell production
Virus Evolution
• What makes a virus a “smart” or “successful”
virus?
– A smart virus is one that does not kill its host right
away; moreover, a smart virus wants to be able to
survive and reproduce for as long as possible without
killing its host.
From an evolutionary standpoint, is Ebola a “smart”
virus?
• What would Darwin say???