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Viruses
Dead or alive?
Viral structure

Viruses are not
cells.
 Basic structure:
– Protein coat
– Nucleic acid core
(RNA or DNA)controls production
of new viruses
Virus Categories

DNA viruses – stable, do not mutate
rapidly
– Single-stranded or double-stranded
– Smallpox, Hepatitis B

RNA viruses – mutate rapidly, unstable
– Single-stranded or double-stranded
– HIV, Rhinovirus
Are viruses alive?
Only 1 characteristic of life: reproduction
 Can only reproduce inside another living
cell= host cell
 Host Cell: provides a home and or food
for a virus…..host harmed by virus
 Process or reproduction = lytic cycle

Lytic Cycle
Virus attaches to host cell’s membrane
and injects its nucleic acid into the host
cell.
 The viral nucleic acid takes over protein
synthesis, creating new viruses.
 The host cell bursts, lyses, releasing the
newly formed viruses.

Before attachment
Attachment
Penetration and uncoating
Release
Assembly
Replication
VIRUS AND HUMANS

Cause a large number of human
diseases
– Ex. Colds, warts, AIDS, measles, flu, small
pox, mumps, hepatitis
VIRUS AND HUMANS

Can be helpful to humans
– Vaccines
– Germ Warfare
– Change genetic material
VIRUS AND HUMANS

Vaccines: weakened virus that doctors
inject into us so our body makes
antibodies (fight disease)
– Ex. Flu shot

After a person has a virus, they produce
antibodies to fight the disease, so they
will never get disease again
– Ex. Chicken pox
VIRUS AND HUMANS

Germ warfare: use viruses to control
pests.
– Ex. Rabbits in Australia

Change genetic material
– Scientist have learned to put genetic
material into viruses
– Hopefully, they’ll be able to use viruses to
replace disease causing DNA in humans