Viruses
Not an Organism!!!!
Therefore, no kingdom or domain
name!!!
Description
• DNA or RNA in a protective coat
DNA -contains genetic instructions
Capsid =Protein Coat -Protects DNA
Sheath -DNA pathway
Tail Fiber –Helps attach to host
Base (End) Plate –
Connects to host cell
Where do they live?
• In a host cell
Common Examples
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Flu virus
Stomach virus
Cold virus
Herpes virus
Chicken pox virus
Measles virus
HIV
Viral meningitis
Mode(s) of Nutrition
• Viruses have no metabolism, so they are
neither heterotroph or autotroph!
Reproduce how?
• Viruses must invade a host cell to
reproduce – they cannot reproduce on
their own.
• They follow 2 types of cycles to do this:
– Lytic Cycle
– Lysogenic Cycle
– Reader p. 300
Lytic Cycle (steps)
• Virus attaches to host cell.
• Virus injects DNA into host.
• Viral DNA takes over host’s metabolism
causing synthesis of new viral proteins
and nucleic acids.
• Viral proteins and nucleic acids assemble
into complete viral particles.
• Viral enzyme lyses the host cell, releasing
new viral particles that can attack other
cells
Lysogenic Cycle
Viral DNA forms a circle
Viral DNA inserts itself into
host cell Chromosome
Viral DNA may replicate with
host cell for many generations
Viral DNA can exit the host
cell’s chromosome
Mumps
Measles
Diagrams of some typical viruses
Classified by:
• Shape and type of cycle they follow
Virus
Bacteria
Viruses differ in shape and in
ways of entering host cells.
• Viruses have a simple structure.
– genetic material (may be DNA or RNA)
– capsid, a protein shell
– maybe a lipid envelope, a protective outer
enveloped
helical
polyhedral
coat
(influenza)
(rabies)
(foot-and-mouth
disease)
capsid
nucleic acid
lipid
envelope
Surface proteins
capsid
nucleic acid
surface
proteins
lipid envelope
surface
proteins
capsid
nucleic acid
Main Groups and Examples
• Omit
How they Help Man
• Viruses are used in genetic engineering
• Viruses are used to fight insect pests
How they hurt man
• Cause diseases: HIV, AIDS, common
cold, chicken pox, flu
=Pathogens!
• Hurt our livestock and crops, costing us $$
Foot and mouth disease causing virus.
Role in Ecosystems
• Omit
• Change to: Treatment and Prevention of
Viral Diseases
Treatment:
There isn’t actually a treatment for the virus
itself but more the symptoms such as a
cold medicine, rest, fluids, etc.
Most vaccines provide protection only if they
are used before an infection begins.
Prevention
• Vaccines Preparation of
weakened or killed
viruses or viral
proteins.
• This stimulates the
immune system,
sometimes producing
permanent immunity
to the disease.