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Viruses Viruses What are they? How do they work? Where do they come from? And… What good are they?
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 nanometers 20nm 1 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 have no envelope – they’re naked! Some viruses are naked!They have no envelope
Some viruses have an envelope to cover them! Envelope – came from host’s cell membrane when virus budded out of host
Viruses don’t reproduce…..TheyReplicate.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 Attachment Lytic Cycle a injection Lysis replication assembly
Sometimes the virus doesn’t kill the cell right away and it becomes part of the cell’s 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.
Assembly lysis Lytic cycle Attachment Replication Viral dna becomes activated Integration – virus DNA joins cell’s DNA Lysogenic cycle Each daughter cell contains both bacterial and viral dna Cell’s DNA (along with viral dna is replicated
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 wasn’t 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 ShapeHost typefunction Retroviruses attack a certain way. DNA viruses attack another way. Animal viruses Plant viruses Bacteria viruses
Retroviruses Contain 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 cell’s DNA. Once part of the cell’s Dna, the viral code can cause the cell to make more viruses.
HIV IS A RETROVIRUS rna CAPSID REVERSE TRANSCRIPTASE
Prions PIECE OF PROTEIN CAUSE OF MAD-COW DISEASE CAN INFECT ANIMALS – INCLUDING HUMANS vIROIDS Single strand of RNA Causes plant diseases Nonviral infectious agents
Human diseases caused by viruses • Common cold • Influenza (flu) • Chickenpox • Polio • HIV • Some pneumonia • Some meningitis • herpes
Animal diseases Distemper Rabies pneumonia Plant Diseases Discolor leaves Stunt growth Kill plants Viruses in the biosphere
Uses for viruses • Vaccines – 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 control • Colorful variations in some plants - flowers
interesting viruses • Ebola 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 – causes The Common cold
Smallpox – once wiped out entire nations, now a memory – Most successful vaccination program in world. Smallpox virus Aren’t you glad there’s no smallpox anymore?
Vaccines – dead or weakened form of virus injected to provide immunity.
First vaccine • Chinese had been using the idea for centuries, but didn’t market it. • Dr. Edward Jenner noticed that milkmaids who had had cowpox rarely got smallpox. • Injected a boy with cowpox pus – he got cowpox • When injected with smallpox pus, he did not get it!