Viruses

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Viruses
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Are viruses living or non-living?

• Nonliving
• Not cells
• Few of lifes criteria
• No respiration
• No growth
• No development
• Can be crystalline, dormant

• Living
• Replicate (with host)
• Contain DNA,RNA
• Contain protein coat

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Virus structure

• Protein Coat
• DNA or RNA for replication
• Adsorb-tion site
• Host specific

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Bacteriophage
Face
Capsid
DNA
Neck
Tail
Base Plate
Tail Fibers
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HIV virus structure
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Viruses
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Are they Alive?

• Smaller and less complex than cells
• Have DNA or RNA enclosed in a protein coat
  called a Capsid
• They do not grow
• No nucleus,cytoplasm,or membrane
• No cellular functions
• Do not generate metabolic energy
• They require a host to reproduce (oligate
  intercellular parasites

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Viruses can be harmful

• Virulent - disease causing
• Temperate - Not immediately disease causing

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Identifying Viruses I

• Type of Nucleic acid
• Single strand RNA
• Double strand DNA
• Physical Structure -shapes
• Icosahedron - capsid has 20 faces
• Helix- capsid coiled intro a spring shape

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Virus Morphologies
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viral capsids
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Identifying Viruses II
Type of host cell viruses very selective about
type of cels they invade (at receptor sites) Type
of Envelope some viruses use lipids from the host
cell to form a layer around the capsid during
replication
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Lytic and Lysogenic cycles
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Lytic cycle of Virulent Viruses

• Absorption -virus attaches itself to cell
• Entry- enzymes weaken cell wall and nucleic
  acid injected into cell
• Replication- viral DNA takes control of cell
  functions

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Lytic cycles

• Replication- viral DNA takes control of cell
  functions
• Assembly-All metabolic activity directed to
  replicating more virus
• Release-Enzymes disintegrate cell -lysing
  releasing new viruses

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Lytic Cycle (Replication) of a Virus - AVIRAL
3. Replication of Viral DNA

• Adsorption of virus onto the host

5.Lysis of Host cell Membrane release Of
virus
4. Assembly of protein coat
2. Insertion of Virus DNA into host cell
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Viral Replication
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Lysogenic cycle of a Temperate Virus

• Virus attaches to host cell,injects DNA into
  cell
• Viral DNA attaches itself to host DNA, becomes a
  new et of DNA genes- called PROPHAGE
• When cell divides, new genes transmitted -
  causes no harm to host but may alter traits

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Transduction
Viral DNA becomes inserted Into the Bacteria DNA
(1/100,000)
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Controlling Viruses
Antiviral Drugs - interfere with the synthesis
of Viral nucleic acid or with the formation of
Viral Capsids during replication Antibiotics-
specifically attacks the metabolism of the
bacterial cell. Antibiotics are useless for
viruses since viruses only use the
reproductive mechanisms of a bacteria.
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Controlling Viruses
Bodys Natural inhibiting ability White Blood
Cells (Leukocytes) - Engulfs viruses and digest
them Interferon- A protein made by cell under
viral attack. This protein binds to the cell
membranes of neighboring cells and interferes
with virus ability to enter cell
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Controlling Viruses
Virus vaccines are made with either inactivated
or attenuated viruses. INACTIVATED VIRUSES- Do
not replicate in host cell. ATTENUATED
VIRUSES- Genetically altered so as not to
cause disease
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Controlling Viruses
Common Viral vaccinations
MUMPS MEASLES RUBELLA HEPATITIS A AND
B CHICKENPOX, SMALLPOX RABIES
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Common Viral Diseases
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Warts are a skin virus!
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4..Bacteriophage

• Bacteria eating virus
• Virus uses the bacteria as a host
• For Viral replication

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Plant peach virus

• 5.Virus can infect
• Plants
• Animals
• Bacteria

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Herpes mouth virus
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Chicken Pox Polio Virus
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Rabies virus Hepatitis B (Liver)
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Cow pox vaccination 1749

• Acquired Immunization
• Artificial injection of a small amount of virus
• Bodys immune response makes antibodies

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HIV Virus
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HIV virus infects T-cells

• HIV virus Weakens the immune system
• AIDS patients die of common diseases when T
  cell (WBC) count falls

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AIDS break down of the immune system death
due to common diseases versus death by AIDS virus
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Genetic Engineering of Insulin
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Restriction EnzymesMade by some Bacteria
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