viruses- chapter 18. objectives know the structure of a virus know some scientists that studied...

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  • Viruses- Chapter 18

  • ObjectivesKnow the structure of a virusKnow some scientists that studied virusesAre viruses living or non-livingKnow how viruses reproduceKnow some examples of viruses and the disease they cause

  • VirusesI. Virus - a tiny, parasitic particle that consists of nucleic acids (DNA or RNA) surrounded by a protein coat. They fall somewhere between living cells and non-living things.HeadDNACollarNeckTail FiberBase PlateSheath

  • Viruses: StructureNOT CELLS!!Viruses containNucleic Acids (DNA/ RNA)A Protein Coat (CAPSID)Some have structures designed to attach to host cells (tail fibers; envelope proteins, spikes, etc)

  • All viruses are made of 2 things:1. DNA/ RNA2. Protein Coat (capsid)

  • Comparing the size of a virus, a bacterium, and an animal cell

  • Why non-living:Viruses cannot reproduce on their own(Must have a living host-cell)2. Viruses cannot metabolize (obtain and use energy)Viruses are not made of cellsViruses do not grow/ developViruses do not respond to stimulusBut Viruses DO have genetic material

  • Scientists1st discovered in 1892 (Iwanowski)Tobacco Mosaic virusOriginally thought to be a bacterial diseaseDisease could be caused even after sap was filtered through extremely small filters

  • 1796 - Edward Jenner - 1st vaccinationInjected cowpox extract into people to immunize them against smallpox..1st vaccination1885 - Louis Pasteurdeveloped rabies vaccination1936 - Dr. William Stanleyisolated tobacco mosaic viruses for the 1st time; obtained them as crystalsLiving organisms do not crystallize, so concluded were not living

  • Sizes of VirusesExtremely small; largest virus is 1/10 size of smallest bacteria. Range in size from 20 - 200 nm (nanometer); 1 nanometer = 1 millionth of a meter

  • Shapes of VirusesHelical - rod-like appearance. Ex: Tobacco mosaic virus Isometrical - spherical or polyhedral shaped; some appear to have spikes for cellular recognition and attachment Ex: Polio or HIV

  • Shapes (cont.)Geometric - usually a geometric pattern; Ex: bacteriophageFilovirus - filamentous strands Ex: Ebola

  • Characteristics of Virusesnon-cellular; do not respire, grow/ develop, respond to stimuliParasitic on living cells - nucleic material in viruses give information for production of new virusesviruses are spread from infected cells by direct contact or indirectly through air, water, food, fecal material

  • Simple Lytic and Lysogenic Cycle to Draw in notes:

  • Viral Reproduction: requires host cellA. Lytic Cycle - the viral replication process that rapidly kills host cell1. A virus invades a host cell and takes controlBegins to replicate immediately producing many new virusesHost cell lyses (breaks apart), releasing the newly made virusesNew viruses may then enter other cells and repeat the cycle.

  • Lytic Cycle

  • B. Lysogenic Cycle - viral replication in which a virus does not immediately kill a host cellvirus attaches to host cell and injects nucleic acid; viral DNA attaches to host cell's chromosomeThe nucleic acid becomes part of the host chromosome (prophage/provirus)Host cell divides, replicating viral DNA along with its own DNAThe viral DNA is activated and enters into the lytic cycle

  • Lysogenic Cycle

  • Lytic vs Lysogenic

  • Lytic vs lysogenichttp://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_2.html

  • Fig. 19-6PhageDNAPhageThe phage injects its DNA.Bacterialchromosome Phage DNAcircularizes.Daughter cellwith prophageOccasionally, a prophageexits the bacterialchromosome,initiating a lytic cycle.Cell divisionsproducepopulation ofbacteria infectedwith the prophage.The cell lyses, releasing phages.Lytic cycleLytic cycleis inducedor Lysogenic cycleis enteredLysogenic cycleProphageThe bacterium reproduces,copying the prophage andtransmitting it to daughter cells.Phage DNA integrates intothe bacterial chromosome,becoming a prophage.New phage DNA and proteinsare synthesized andassembled into phages.See Review Sheet

  • ***Retrovirus virus contains RNA and enzyme called reverse transcriptasevirus attaches to target cell and inject RNA and reverse transcriptasethe reverse transcriptase reads the RNA and produces DNAthe new viral DNA begins the lytic cyclewhen the viruses emerge from the infected cell, they often surround themselves with the cells plasma membrane material making it harder for the bodys defenses to recognize it. Ex: HIV

  • Reverse Transcription videoRNA DNA RNA Protein

    Viral RNA is converted into host DNA (reverse transcription), which is then integrated into the host genome. Then when normal transcription occurs, the viral message is expressed, synthesizing a viral protein.

  • Types of virusesBacteriophage infects bacteriaPapovavirus (DNA) causes wartsAdenovirus - (DNA) respiratory infectionsHerpesvirus - (DNA) causes herpes, chicken pox, shinglesParvovirus (DNA) infects dogsRhinovirus (RNA) common coldHIV Human immunodeficiency virus retrovirus (RNA) causes AIDS (Auto Immune Deficiency Syndrome)

  • T4 bacteriophage infecting an E. coli cell

  • Viruses are pathogenicTreatment: Really no treatment for viral diseases Interferon therapy (IF) has some beneficial effectsPREVENTION IS CRUCIAL: Vaccination; sterilization, proper hygiene, avoidance of contagious individuals

  • Ways to prevent viral infectionSterilization with disinfectants (cleaners)Disinfectants are used to sterilize hospitalsAvoid contactVaccinations build up antibodies for future infection

  • Herd Immunity

  • Human Immunodeficiency VirusRetrovirusInformation is stored in RNA (mutates easily); hijacks host-cell DNA

    Attacks helper T cells in the immune system and lowers the immune system

    Causes Auto Immune Deficiency Syndrome

  • Defenses Against Viral Infection1st line of defense skin, mucous membranes, tearsMost viruses enter body through nose or mouth2nd line of defense (once inside body)1. White blood cells called phagocytes engulf and destroy invading virus2. Immune response body detects foreign proteins called antigens. The body then produces antibodies to attack invader

  • Vaccine a solution of weakened or killed pathogens (disease-causing organism) that causes the body to produce antibodies without causing the disease. The immune system remembers the pathogen in case it encounters it again.

    3rd Interferon (IF) a protein that interferes with viral replication it is produced by cells under viral attack which triggers healthy cells to produce protective enzymes. IF works faster than antibody production.

  • Viroids & PrionsViroids single stranded RNA molecules that have NO surrounding capsids. Infect many plants, including potatoes, tomatoes, apples, and citrus fruits.Prions protein infectious particles. Bovine Spongiform Encephalopathy (mad cow disease) and Creutzfeldt-Jakob disease, a similar disease in humans, may be caused by prions.

  • Flu Attack! How a Virus Invades your Bodyhttp://www.youtube.com/watch?v=Rpj0emEGShQ

  • Lytic & Lysogenic Cycle and Virus vs Cells DiagramsGet a textbook and a sheet of paperTurn to page 481:On ONE side of the paper, draw the diagram in figure 19-10 comparing the lytic and lysogenic cycles. Be sure to include all text/ infoTurn to page 483: On the OTHER side of the paper, draw Figure 19-11 comparing viruses and cells. Be sure to include all text/ info

    **************Figure 19.6 The lytic and lysogenic cycles of phage , a temperate phage

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