virus definition non-living particle that causes disease pathogen: any agent that causes disease...
TRANSCRIPT
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VIRUS DEFINITION Non-Living particle that causes disease Pathogen: any agent that causes disease
Human papillomavirus: cause of sexually transmitted infections like genital wartssmallpox
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HISTORY OF VIROLOGYSmallpox epidemics
Reached epidemic size before 1800 Thousands died or survivors were disfigured Survivors were thereafter immune Started inoculating with a mild form Problem: risk of dying!
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HISTORY OF VIROLOGYMilkmaids and Cowpox
Milkmaids seemed immune to smallpox Milkmaids often got cowpox (harmless) Use cowpox to safely immunize
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HISTORY OF VIROLOGY1796 Edward Jenner
Took matter from cowpox sore on milkmaid Injected cowpox matter into a boy Inoculated boy with smallpox
Boy remained healthy!
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VIRUSES SEEM ALIVE
Contain protein and DNA or RNA Reproduce Evolve
HIV has an amazing knack for evolving
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VIRUSES DON’T SEEM ALIVE!
Obligate parasites: must have host cell Cannot move: spread by wind, water, food, secretions Smaller than bacteria: 20 to 250 nanometers
100 flu viruses = length of 1 bacterium!
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VIRUSES ARE NOT CELLS
NOTE: No cell membrane, nucleus or organelles!
CAPSID (protein coat)
CORE (DNA or RNA)
SPIKES (chemical recognition)
ENVELOPE (surrounds capsid)
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How do viruses spread?
Virus is non-living outside the host cell Spread by air, water, food, body fluids
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HOW DO VIRUSES RECOGNIZE A HOST?
Glycoproteins: spikes of carbohydrate + protein Embedded in viral envelope
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HOW DO VIRUSES RECOGNIZE A HOST?
Viral glycoproteins can recognize receptor proteins on the host cell
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How do viruses find a host cell?
Virus needs to recognize host cell before infection Envelope protein “fits” host receptor molecule
lock
key
envelope protein
host receptor molecule
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How are viruses classified?
Not classified in any kingdom of life Classification is based on 3 characteristics
1 capsid helical, icosahedral,
spherical, head and tail, or filamentous?
2 envelope present or absent?
3 nucleic acid DNA or RNA?
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What is a helical capsid? In some viruses the capsid or protein coat is a
corkscrew shape
RNA
capsid
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What is an icosahedral capsid?
capsid
DNA
In some viruses, like the polio virus, the capsid or protein coat, is a geometric shape
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What is a spherical capsid?
capsidRNA
In some viruses, like the influenza virus, the capsid or protein coat, is a ball shape
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What is a filamentous capsid?
In some viruses, like the Marburg virus or the ebola virus, the capsid or protein coat, is a stringy shape
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What is a Head and Tail capsid?
In some viruses, like a bacteriophage, the capsid or protein coat, is a stringy shape
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HOW DO VIRUSES REPLICATE?The Lytic Cycle
(DNA) + TRANSLATION (CAPSIDS)
: DNA + CAPSIDS
LYSIS!
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HOW DO VIRUSES REPLICATE?The Lysogenic Cycle
lysis
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AIDS (Acquired Immune Deficiency Syndrome)
Caused by Human Immunodeficiency Virus (HIV) Symptoms: immune system failure Transmission
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AIDS (Acquired Immune Deficiency Syndrome)
Structure and size: enveloped icosahedron, 125 nm Specificity: single host, human Perhaps 2 million Americans infected Much worse in Africa and Caribbean
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HIV Replication
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AIDS (Acquired Immune Deficiency Syndrome)
Prevention means lowering transmission Potential cures
Interfere with
RNA transcriptase Interfere with
translation of protein