viruses what are they? how do they work? where do they come from? and… what good are they? viruses
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What are they?How do they work?Where do they come from?And What good are they?Viruses
What is a virus?An infectious agent made up of: a core of nucleic acid DNA or RNA(ONLY ABOUT 5 GENES)
a protein coat (capsid)
How Big are viruses?Polio virus = 20 nanometers20nm1 nm 0ne billionth of a meter!3000 polio viruses fit across the diameter of a period at the end of a sentence in your book.
Some viruses are naked!They have no envelopeSome viruses have no envelope theyre naked!
Some viruses have an envelope to cover them!Envelope came from hosts cell membrane when virus budded out of host
Viruses dont reproduce..They Replicate.
Once inside a cell, the cell does all the work and produces new viruses using the inserted Dna or Rna as a Guide.
The lytic cycle
Sometimes the virus doesnt kill the cell right away and it becomes part of the cells genes.If this happens, the virus DNA becomes a prophage and can become activated at any time (like a time bomb).In the meantime, the prophage is passed on to all the offspring of that cell . Maybe for many generations.
Lysogenic cycleLytic cycleAttachment
Integration virus DNA joins cells DNACells DNA (along with viral dna is replicated
Each daughter cell contains both bacterial and viral dnaViral dna becomes activatedReplication
Are viruses living or nonliving?What are some characteristics of life?
Do viruses exhibit these characteristics?
When were viruses discovered?Viruses have apparently always been around.However, it wasnt until 1897 that a Dutch scientist named Beijerinck called an invisible agent that was smaller than bacteria a virus (Latin for poison). He was studying tobacco leaves that had been infected with what we now know as tobacco mosaic virus.
Classification of Viruses By Shape Host type functionRetroviruses attack a certain way.
DNA viruses attack another way.
Animal virusesPlant virusesBacteria viruses
RetrovirusesContain RNA When infecting a cell, these viruses have to transcribe the RNA to DNA before the viral code can be read.This requires an enzyme, reverse transcriptase, to Change RNA to DNA then the viral code can be added to the cells DNA.Once part of the cells Dna, the viral code can cause the cell to make more viruses.
HIV IS A RETROVIRUSREVERSE TRANSCRIPTASErnaCAPSID
Nonviral infectious agentsPrionsPIECE OF PROTEINCAUSE OF MAD-COW DISEASE CAN INFECT ANIMALS INCLUDING HUMANSvIROIDSSingle strand of RNACauses plant diseases
Human diseases caused by viruses Common coldInfluenza (flu)ChickenpoxPolioHIVSome pneumoniaSome meningitisherpes
Viruses in the biosphereAnimal diseasesDistemperRabiespneumoniaPlant DiseasesDiscolor leavesStunt growthKill plants
Uses for virusesVaccines dead or weakened form that stimulates the immune system to fight the virus when exposed to it.
Genetic engineering use a virus carrier to insert genes into diseased cells.
Agriculture Pest controlColorful variations in some plants - flowers
interesting virusesEbola virus kills quickly; requires close contact, such as when preparing a body for burial or using dirty needles; since it kills so fast, it generally dies out quickly.
Human sarcoma virus causes tumors
Adenovirus causesThe Common cold
Bacteriophages infect bacteria; very well studied.
Smallpox once wiped out entire nations, now a memory Most successful vaccination program in world.Smallpox virusArent you glad theres no smallpox anymore?
Vaccines dead or weakened form of virus injected to provide immunity.
First vaccineChinese had been using the idea for centuries, but didnt market it. Dr. Edward Jenner noticed that milkmaids who had had cowpox rarely got smallpox.Injected a boy with cowpox pus he got cowpoxWhen injected with smallpox pus, he did not get it!