ch. 19 warm-up 1. why do many scientists classify viruses as non-living? 2. draw the basic structure...
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Ch. 19 Warm-upCh. 19 Warm-up
1. Why do many scientists classify viruses as non-living?
2. Draw the basic structure of a virus. Label and define capsid, viral envelope and nucleic acid.
Ch. 19 Warm-upCh. 19 Warm-up
1. Draw the lytic/lysogenic cycle.
2. What stage of the lytic-lysogenic cycle is a virus virulent? Temperate?
3. What determines a host range?
VirusesVirusesChapter 19
What you must know:What you must know:The components of a virus.The differences between lytic and
lysogenic cycles.
Bacteria vs. VirusesBacteria vs. Viruses
Bacteria VirusProkaryotic cellMost are free-living
(some parasitic)Relatively large sizeAntibiotics used to kill
bacteria
Not a living cell (genes packaged in protein shell)
Intracellular parasite1/1000 size of
bacteriaVaccines used to
prevent viral infectionAntiviral treatment
VirusesVirusesVery small (<ribosomes)Components = nucleic acid + capsid
◦Nucleic acid: DNA or RNA (double or single-stranded)
◦Capsid: protein shell◦Some viruses also have viral envelopes that surround capsid
Limited host range (eg. human cold virus infects upper respiratory tract)
Reproduce within host cells
Simplified viral replicative cycleSimplified viral replicative cycle
BacteriophageBacteriophageVirus that infects bacterial cells
VIDEO: VIDEO: T4 PHAGE INFECTION
Lytic Cycle of T4 Lytic Cycle of T4 PhagePhage
Bacteriophage Bacteriophage ReproductionReproduction
Lytic Cycle:Lytic Cycle:◦Use host machinery to make copies of
virus◦Death of host cell by rupturing it (lysislysis)◦Virulent phages replicate by this method
Lysogenic Cycle:Lysogenic Cycle:◦Phage DNA incorporated into host DNA
and replicated along with it◦Phage DNA = prophageprophage
Temperate Phage: uses both methods of replication
Lytic Cycle vs. Lysogenic Lytic Cycle vs. Lysogenic CycleCycle
Animal virusesAnimal viruses have a membranous have a membranous envelopeenvelope
Host membrane forms around exiting virus
Difficult for host immune system to detect virus
VIDEO: VIDEO: HOW DENGUE VIRUS ENTERS A CELL
RetrovirusRetrovirusRNA virus that uses reverse reverse
transcriptasetranscriptase (RNA DNA)Newly made viral DNA inserted into
chromosome of hostHost transcribes viral DNA (= provirusprovirus)
to make new virus partsExample: HIV (Human Example: HIV (Human
Immunodeficiency Virus)Immunodeficiency Virus)
HIV = HIV = RetroviruRetroviru
ss
HIVHIV
◦Infects white blood Infects white blood cellscells
◦HIV+HIV+: : provirus provirus (DNA inserted)(DNA inserted)
◦AIDSAIDS: active viral : active viral reproduction reproduction
Other Human VirusesOther Human VirusesHerpes virus Smallpox
Herpes Simplex Virus 1 (HSV-1)
Herpes Simplex Virus 2 (HSV-2)
Eradicated in 1979 due to worldwide vaccination campaigns
EbolaEbola TransmissionTransmission: contact with contaminated
blood or bodily fluids SymptomsSymptoms: fatigue, fever, severe
headache, vomiting, diarrhea, rash, bleeding◦ May appear 2-21 days after exposure
EbolaEbola TreatmentTreatment:
◦ Intravenous fluids, balance electrolytes◦ Experimental: antiviral drugs, plasma
transfusions from survivors, antibodies (Zmapp)
◦ No vaccine (yet) StatisticsStatistics:
◦ 2014 Ebola Outbreak (worldwide): 21,382 cases, 8474 deaths (*as of 1/19/15)
◦ Seasonal Influenza: estimated 36,000 deaths in U.S. each year (2015: mutated H3N2 strain)
2014 Ebola Outbreak2014 Ebola Outbreak
Cumulative Ebola CasesCumulative Ebola Cases
VaccinesVaccinesWeakened virus or part of
pathogen that triggers immune system response
Emerging virusesEmerging viruses = mutation of = mutation of existing virusesexisting viruses
ViroidsViroidsSmall, circular RNA
molecules that infect plants
Cause errors in regulatory systems that control plant growth
Eg. coconut palms in Philippines
PrionsPrionsMisfolded, infectious proteins that
cause misfolding of normal proteinsEg. mad cow disease
(BSE),Creutzfeldt-Jakob disease (humans), scrapie (sheep)
Diseases caused by prionsDiseases 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 diseases