Môn Sinh học - Chapter 19: Viruses

Ch. 19 Warm-upWhy do many scientists classify viruses as non-living?Draw the basic structure of a virus. Label and define capsid, viral envelope and nucleic acid.Ch. 19 Warm-upDraw the lytic/lysogenic cycle.What stage of the lytic-lysogenic cycle is a virus virulent? Temperate?What determines a host range?VirusesChapter 19What you must know:The components of a virus.The differences between lytic and lysogenic cycles.How viruses can introduce genetic variation into host organisms.Mechanisms that introduce genetic variation into viral populations.Bacteria vs. VirusesBacteriaVirusProkaryotic cellMost are free-living (some parasitic)Relatively large sizeAntibiotics used to kill bacteriaNot a living cell (genes packaged in protein shell)Intracellular parasite1/1000 size of bacteriaVaccines used to prevent viral infectionAntiviral treatmentVirusesVery small (<ribosomes)Components = nucleic acid + capsidNucleic acid: DNA or RNA (double or single-stranded)Capsid: protein shellSome viruses also have viral envelopes that surround capsidVirusesLimited host rangeEntry = attach to host cell membrane receptors through capsid proteins or glycoproteins on viral envelope (animal)Eg. human cold virus (rhinovirus)  upper respiratory tract (mouth & nose)Reproduce quickly within host cellsCan mutate easilyRNA viruses: no error-checking mechanismsSimplified viral replicative cycleVIDEO: T4 PHAGE INFECTIONViral ReproductionLytic Cycle:Use host machinery to replicate, assemble, and release copies of virusVirulent phages: Cells die through lysis or apoptosisLysogenic (Latent) Cycle:DNA incorporated into host DNA and replicated along with itBacteriophage DNA = prophage Animal virus DNA = provirusUV radiation, chemicals: lysogenic  lytic cycleTemperate Phage: uses both methods of replicationBacteriophageVirus that infects bacterial cellsLytic Cycle of T4 PhageLytic Cycle vs. Lysogenic CycleAnimal viruses have a membranous envelopeHost membrane forms around exiting virusDifficult for host immune system to detect virusVIDEO: HOW DENGUE VIRUS ENTERS A CELLVIDEO: HIV LIFE CYCLERetrovirusRNA virus that uses reverse transcriptase (RNA  DNA)Newly made viral DNA inserted into chromosome of host (provirus)Host transcribes provirus to make new virus partsExample: HIV (Human Immunodeficiency Virus)HIV = RetrovirusOrigin: Chimpanzee virusInfects white blood cells (helper T)HIV+: provirus (DNA inserted), latentAIDS: <200 WBC count, opportunistic infectionsHIVOther Human VirusesHerpes virusSmallpoxHerpes Simplex Virus 1 (HSV-1)Herpes Simplex Virus 2 (HSV-2)Eradicated in 1979 due to worldwide vaccination campaignsEmerging Viruses = mutation of existing virusesPandemic: global epidemicCurrent OutbreaksZika VirusSpread by Aedes mosquitoes (Aedes aegypti)Major outbreak in Brazil and Latin AmericaLinked to birth defects (microcephaly)Dengue FeverChikungunyaZika Virus (as of Dec. 2015)Drugs for Prevention/TreatmentVaccine: weakened virus or part of pathogen that triggers immune system response to prevent infectionEx. HPV, MMR, HepA, Flu shotAntiviral Drugs: block viral replication after infectionEx. Tamiflu (influenza), AZT (HIV)ViroidsSmall, circular RNA molecules that infect plantsCause errors in regulatory systems that control plant growthEg. coconut palms in PhilippinesPrionsMisfolded, infectious proteins that cause misfolding of normal proteinsEg. scrapie (sheep), mad cow disease (BSE), Creutzfeldt-Jakob disease (humans), kuru (humans – New Guinea)Diseases caused by prionsPrions act slowly – incubation period of at least 10 years before symptoms developPrions are virtually indestructible (cannot be denatured by heating)No known cure for prion diseasesKuru in New GuineaPrion Neurodegenerative DiseasesAlzheimer’s DiseaseParkinson’s DiseaseAMOEBA SISTERS: VIRUSES: VIRUS REPLICATION AND THE MYSTERIOUS COMMON COLDTED-ED: HOW WE CONQUERED THE DEADLY SMALLPOX VIRUS