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Transcript
Viruses Obj: n Why no kingdom for viruses? n Know basic viral anatomy; especially HIV & bacteriophage n Know stages of 2 life cycles n Harmful and beneficial effects n Know several examples of treatments Virus Introduction I. General info: A. B. C. D. Pathogens (cause diseases) in all 6 kingdoms. Virulence is a term used to refer to the relative ability to do harm or damage to a host. Epidemic – a widespread outbreak of an infectious disease at a specific time. Pandemic – a worldwide or multiple continent outbreak of an infectious disease. D. Doesn’t belong to a kingdom because they are not considered to be alive. 1. They need to invade or infect a host cell to reproduce 2. They do not carry out the most basic metabolic processes, like using or producing energy, no wastes. 3. They don’t really have any working parts: i.e. no nucleus, mitochondria, ribosome's and some even lack cytoplasm. II. Viral Structure A. B. All viruses are small, only visible through electron microscope Consist of two parts: 1. Nucleic acid core. 2. Outer protein coat called a “capsid”. a) Protein coat determines the shape of the virus. b) Some viruses (animal) have membranous outer envelope instead of/or on top of a protein coat C. Three basic shapes: 1. Polyhedral Virons – This shape group includes the classic virus shape that looks like a dodecahedron. A dodecahedron is a geometric shape with twelve (12) sides. e.g. 2. Adenovirus (respiratory virus) or HIV. Spiral (helical)- They are set up like a tube. The protein coat winds up like a garden hose around the core. e.g. tobacco mosaic virus 3. Complex virons - geometric head and long legs. e.g. bacteriophage Receptor proteins Reverse transcriptase Protein coat RNA Envelope IV. Two Types of Viral Infection Pathways: (page 481) A. Lytic Infection (about 25 minutes) 1. Attachment -virus attaches itself to the receptor site of host cell. a) Viruses are very specific about their host. b) In some cases the virus is engulfed by the host cell. 2. Injection -virus use enzymes to enter the cell wall of host and its nucleic acid is injected into the host cell. 3. Replication - host’s DNA disintegrates and viral DNA or RNA takes over the host cell. 3. Replication continued a) Host cell replicates (copies) viral nucleic acids, coat proteins, and viral enzymes. b) RNA viruses (retroviruses) have special reverse transcriptase enzyme to change its RNA into DNA. 4. Assembly -Viral parts are put together to form new complete viral units. 5. Release or Lysis -New viruses release enzymes to break down host’s cell wall (killing the host cell) and they are released to invade other host cells. a) Some animal viruses bud off new viral particles. Lytic Cycle Movie B. Lysogenic (Prophage) Cycle (pg 481) 1. 2. 3. 4. 5. Attachment - Same as Lytic Injection- Same as Lytic Splicing - The viral DNA is spliced into the DNA of the host. Cellular Duplication - During normal cell division the viral DNA is also duplicated and passed on with the cell’s own DNA Activation - An environmental stress stimulates the activation of the viral DNA and stages 3-5 of the lytic cycle begin Harmful Effects of viruses Route Skin contact Respiratory Fecal-oral Milk Transplacental Sexually Insect vector Animal bite Examples HPV- Human papilloma virus (warts) Cold viruses, influenza, measles, mumps, rubella Polio, echo, Coxsackie, Hepatitis A, Rotavirus HIV, HTLV-1, CMV Rubella, CMV, HIV Herpes 1 and 2, HIV, HPV, Hepatitis B Yellow fever, Dengue fever, Zika Rabies CMV - cytomegalovirus, HPV, HTLV – Human T-Lymphotropic virus disorders Chicken Pox Mumps Measles Beneficial Effects of viruses A. Can be used to insert desirable genetic information into cells. 1. 2. B. Genetically engineered organisms like tulip coloration Deliver correct genes into human cells. Possible antibiotic (kills bacteria) VI. Combating Viral Infections? A. B. Antiviral Drugs: 1. AZT (HIV), Acyclovir (herpes), or Vidarabine (encephalitis) treat the immediate symptoms, but are not a cure Vaccine 1. Make a virus less harmful (virulent): a. Grow in different host cell, e.g. flu vaccines are grown in chicken eggs so the flu virus will look for chicken cells instead of human cells. b. Find a less harmful, but similar looking virus, e.g. cow pox vs small pox. c. Chemically alter or destroy the nucleic acid of the virus, e.g. polio virus was treated with formaldehyde. B. Vaccine continued 2. Leave some of the viruses outer coat intact. Why? n 3. 4. 5. So our immune system will react to it. Inject vaccine A person’s immune system reacts to the less harmful virus and forms memory white blood cells (WBC’s). When you get exposed to the virulent form of the virus your immune system responds so quickly that you won’t get sick or your sickness is less then a non-immunized person would experience. How We Conquered Smallpox