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Viruses
Virus Facts
 Nonliving
particle that invade
the cells of plants, animals,
fungi, and bacteria.
 Often destroy the cells they
invade
 Virology is the study of
viruses
History of Virology
 Wendell
Stanley crystallized
the tobacco mosaic virus in
1935
 Discovered that it may be a
chemical rather than a cell
Tobacco Mosaic
Virus
Characteristics
 No
Growth
 No Homeostasis
 No Metabolism
 Can Mutate
 May contain DNA or RNA
Characteristics
 Can
only reproduce in a host
cell
 Made up of a nucleic acid
core, protein coat, and in
some cases an envelope
–The coat protects the genetic
material
–Enables the virus to invade its
host cell
Virus
Viral Shape
 Determined
by capsid or
its nucleic acid
 Icosahedron-20 triangular
faces - herpes simplex,
chicken pox, polio
 Helix - a coiled spring rabies, measles, tobacco
mosaic virus
Icosahedron
Helix
DNA Viruses
 Virus
may directly produce
DNA that then makes more
viral proteins
 May join with the host cell’s
DNA to direct the synthesis
of new viruses
 Chicken pox, mono, herpes
DNA Viruses
RNA Viruses
 Viral
RNA is released into
the host cell’s cytoplasm
 Uses the host cell’s
ribosomes to produce new
viral proteins
RNA Viruses
Retroviruses
 RNA
Viruses
 Contains an enzyme
called reverse
transcriptase.
 Uses a template to make
DNA
Viruses
Viroids and Prions
 Viroids
- smallest known
particles that are able to
replicate
–Consist of a short, single
strand of RNA and has no
capsid
–Disrupt plant cell metabolism
and damage crops
Viroid
Viroids and Prions
 Prions
- abnormal forms of
protein that clump
together inside a cell
–Clumping kills the cell
–Scrapies, Mad Cow
Prion
Bacteriophage
 Viruses
that infect bacteria
 Viral nucleic acid head, a
collar, a sheath, which makes
up the tail, together making
the capsid. There is also a
base plate and tail fibers.
Animation
 http://www.hybridmedicala
nimation.com/anim_bacter
iophage.html
The Lytic Cycle
 Destroys
the host cell
–Attachment
–Entry
–Replication
–Assembly
–Release – Released viruses
are called progeny
Lysogenic Cycle
 These
viruses do not destroy
the host immediately
–Attachment
–Injection
–Integration
–Cell multiplication
Lysogenic
Transmission of
Diseases
 Human
contact
 Air
 Water
 Insect
bites
Prevention and
Treatment
 Antiviral
drugs
–Interfere with viral nucleic
acid synthesis
–Already infected patients
Prevention and
Treatment
 Vaccination
–Inactivated
• Do not replicate in a host
system
–Attenuated
• Genetically altered so they are
incapable of causing disease
Emerging Viruses
 Newly
discovered viruses
 Exist in isolated habitats, but
infect humans when habitats
are developed.
–Ebola found in the Democratic
Republic of Congo
Viruses and Cancer
 Lysogenic
viruses may
trigger cancer genes
–Hepatitis B
–Epstein-Barr
More terms to know
 Eradication
 Lysis
 Capsid