Viruses

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Viruses

• Chapter 18 Pg 489-499

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What are Viruses

• A virus is a non-cellular particle made up of
  genetic material and protein that can invade
  living cells.
• Non-living doesnt carry out respiration, grow,
  develop, or reproduce on its own
• Living cells used in replication host cells

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Naming Viruses

• Viruses are not named like living organisms, i.e.
  using binomial nomenclature. 
• Named after
• the disease it causes (ex. Rabies, polio)
• named after the person(s) who discovered them
• after tissue they infect (ex. Adenovirus infects
  adenoid tissuecommon cold)
• Some given a genus and species name or code number

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T4 Bacteriophage
Bacteriophage a virus that infects bacteria.
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The Structure Of a Virus

• a core of nucleic acid (DNA or RNA)
• Nucleic acid core is surrounded by a protein coat
  (capsid)
• Some viruses have additional envelope (made of
  cell membrane parts)
• ex. Human flu

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THE END

• Viruses come in many shapes and sizes
• Protein arrangement determines shape
• Shape determines cells that can be infected
  (page 491)

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The Influenza Virus!
1918 Influenza or Spanish flu Protein.
Common flu structure
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Spanish Flu continued

• http//www.pbs.org/wgbh/nova/sciencenow/video/3318
  /q02-220.html
• What does all this mean?

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Viruses use Host Cell to Replicate

• Virus recognizes and attaches to host cell
• Each virus has specifically shaped proteins that
  interlock with receptor sites on host cell

• Viruses are mostly species specific or cell type
  specific
• Smallpox is said to be eradicated because it is
  human specific
• Flu is not human specific

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Viral Replication

• Virus inject nucleic acid into cell
• A virus can have two different cycles of
  replication lytic and lysogenic

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Viral Replication Cycles Lytic Cycle

• Lytic Cycle
• A. Virus attaches to cell
• B. Nucleic Acid is injected into cell
• C. Host cell makes viral nucleic acid and
  proteins
• D. New virus particles are assembled
• E. Host cell breaks open to release new virus
  particles

• Analogy
• An army tank (virus) filled with enemy troops
  (nucleic acid)
• Crashes through the wall of an automobile factory
  (host cell)
• Troops take over factorys machinery (nucleus)
  and adapt them to make new tanks (viruses)
  instead of cars (cell parts)

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Viral Replication Cycles 2 Lysogenic

• Lysogenic Cycle
• A. Virus attachment and entry into cell
• B. Viral nucleic acid becomes part of hosts
  chromosomes (provirus - viral DNA that is part of
  the host cells chromosomes)
• C. Viral nucleic acids are replicated during
  chromosome replication
• At some point it will enter lytic cycle

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Lytic vs. Lysogenic Examples

• Lytic Measles, cold viruses
• Lysogenic shingles, warts, HIV

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Disease Symptoms of provirus's

• Cold sores herpes simplex I virus
• - virus remains in cells as provirus, when
  enters lytic cycle, new cold sore erupts
• Possible triggers for activating lytic cycle
  physical stress (ex. Sunburn), emotional stress
  (ex. Anxiety)
• Chicken poxlater becomes shingles

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Release of viruses

• Lysis bursting of cell
• Exocytosis

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Cycle of Lytic and Lysogenic
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Flu viruses are spread mainly from person to
person through

• coughing, sneezing or talking by people with
  influenza.
• Sometimes people may become infected by touching
  something such as a surface or object with
  flu viruses on it and then touching their mouth
  or nose.

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Vaccines

• Viruses grown on chicken embryos are attenuated
  vaccines
• Another type of vaccine is made by heat killing
  the virus
• These non-harmful forms of virus are injected
  into body so that the body can learn how to
  defend itself

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Retrovirus

• Nucleic Acid is RNA (not DNA)
• Once RNA is injected into host cell, it will make
  viral DNA with help from an enyzme (reverse
  transcriptase)
• Viral DNA becomes a provirus (page 495)

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HIV infection of white blood cells

• Infected host cells function normally provirus
• No symptoms can still transmit virus in body
  fluids
• White blood cells will be lost when provirus
  enters lytic cycle
• Immune system is compromised

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HIV Info

• HIV becomes AIDS when the number of immune cells
  drops below a predetermined number
• No one dies from HIV or AIDS people die from
  secondary infections (ranging from the common
  cold to cancer)
• More than 3 million people (size of Chicago) die
  each year
• There are approx. 14,000 new cases of HIV
  worldwide every day

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Viruses and Cancer

• Retroviruses may cause cancer - Normal cells
  become tumor cells
• DNA viruses, papilloma virus (HPV) and hepatitis
  B virus may cause cancer