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VIRUSES
- Small non-cellular particles
- Seen only with an electron microscope
- Classified according to their shape
- Classified according to their molecular structure
COMMON VIRAL NAMES:
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Herpes
Influenza
HIV
Smallpox
Cowpox
Polio
Hepatitis
Rabies
Chicken pox
Mono
Cancer (HPV)
Mono
Shingles
IN ORDER TO STUDY
VIRUSES…. WE MUST:
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Isolate it from its host
Hosts could be:
animals
plants
bacteria
cells
• Inside the host it
produces new viruses
• All viruses have one
type of nucleic acid:
DNA or RNA
• Most viruses are
haploid
• Viral nucleic acid is
covered by a protein
coat (called a
CAPSID)
SHAPES OF VIRUSES
• Two shapes: cubic symmetry & helical
symmetry
• CUBIC
• HELICAL
CHEMISTRY OF VIRUSES
• Most viruses have no enzymes
• Cannot make protein on its own
• Require the protein synthesis machinery of
its host cell
• Cannot make their own ATP
• Act as intracellular parasites
• Replicate themselves by making copies if
their parts which are assembled using host
building block materials
• Viruses do not grow
bigger then divide
• They dissemble,
make new parts, they
assemble parts
identical to the parent
virus
• All of this takes place
in the host cell
• Are viruses living ?
DIFFERENCES BETWEEN VIRUSES & CELLS
VIRUS
CELLS
• DNA or RNA, in
various forms as the
genetic info.
• Few proteins, mainly
as a cover for nucleic
acid
• Few or no enzymes
• Cannot make ATP
• Intracellular synthesis
then assembly
• Always both DNA &
RNA as genetic info.
• Hundreds of proteins
in various structures
• All have sugars &
lipids
• Hundreds of enzymes
• Makes ATP
• Division by mitosis or
fission
VIRAL REPLICATION
• ATTACHMENT & entrance: virus
chemically recognized its host & attach to
it.
• Whole virus or only its DNA or RNA enters
its host cell
• SYNTHESIS of protein and nucleic acid
• Molecular info. Inside the virus directs the
host cell to replicate viral proteins
• ASSEMBLY of the units:
• The viral nucleic acids, enzymes, and
proteins are brought together and
assembled into new viruses
• RELEASE of new virus particles:
• Newly formed viruses released from
infected cell and the host cell dies
LYTIC & LYSOGENIC CYCLES OF VIRUSES
• LYTIC CYCLE can be completed in as little as
25-45 minutes
• 300 new viruses can be produced
• Lysis = destruction or bursting open of host cell
releasing new viruses
• BACTERIOPHAGES (viruses that infect
bacteria) cause cell lysis (cell death)
• LYSOGENIC CYCLE = replicated viruses
can lay dormant inside their host
• Dormant virus can be activated by stress,
temperature increases above 37 degrees,
lack of certain food nutrients.
VACCINES
• VACCINES are
solutions that are
prepared from viral
components or
inactivated viruses
• Body reacts to
vaccine as if it were a
real virus and
produces antibodies
I HAVE LIKELY BEEN
VACCINATED AGAINST:
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Chicken pox
Polio
Measles
Mumps
Rubella
Influenza
HPV
hepatitis
Your Dog & Cat Against….RABIES