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VirusesObjectivesIdentify different types of virusesCompare replication cycles Discuss how viruses cause disease
The Viruses• Viruses are noncellular and thus cannot be
classified with cellular organisms• Generally smaller than 200 nm in diameter• Usually named after the diseases they cause
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Viral Structure• Each type has at least two parts
– Capsid: Outer layer composed of protein subunits• Some enveloped by membrane• Others “naked”
– Nucleic acid core: DNA or RNA
• Vary in shape from thread-like to polyhedral
Virus Structure
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Parasitic NatureViruses are:
Obligate intracellular parasites Cannot reproduce outside a living cell
Can be cultured only inside living cells Chicken egg Tissue culture
Most are host specific
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Viral CategorizationClassification is based on:
Type of nucleic acidSize and shapePresence / absence of outer envelope
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The Bacteriophages:ReproductionBacteriophages – Viruses that infect bacterial
cellsPortions of capsid adhere to specific receptor
on the host cellViral nucleic acid enters the cellOnce inside, the virus takes over metabolic
machinery of the host cell
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Bacteriophages:The Lytic CycleLytic cycle may be divided into five stages:
AttachmentPenetrationBiosynthesisMaturationRelease
Kills the host cell
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The Bacteriophages:The Lysogenic CyclePhage becomes a prophage (provirus)
Becomes integrated into the host genomeBecomes latent
May later reenter the lytic cycle
Doesn’t kill the host (at first anyway)Disease causing viruses
Herpes simplex I (cold sores) and II (genital herpes), and hepatitis B, chicken pox (shingles)
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Reproduction of Animal VirusesAnimal virus enters the host cellUncoating releases viral DNA or RNA
Budding: Viral particles released in a bud Acquires a membranous envelopeExamples:
Retroviruses (HIV >>>>AIDS) Contain reverse transcriptase Carries out RNA cDNA reverse transcription cDNA becomes integrated into host DNA
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Viral Infections• Viruses are best known for causing
infectious diseases in plants and animals• Examples:– Herpes, HIV, cancer• Viruses lack metabolism; thus, antibiotics have no
effect– Viroids• Naked strands of RNA• Many crop diseases
– Prions• Protein molecules with contagious tertiary structure• Some human and other animal diseases - Mad cow
disease
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Diseases caused by viruses:In HumansCold/fluMeaslesHerpespolioSmallpox
WartsHIVmononucleosis
In AnimalsDistemperFoot and Mouth diseaseFeline LeukemiaIn PlantsTobacco Mosaic Disease
Control of VirusesWhite Blood Cells in humans
AntibodiesInterferon (chemical produced in the body)
Vaccines
Examples of Viruses
18-2 Archaebacteria and EubacteriaObjectivesCompare types of ProkaryotesExplain the characteristics and adaptations of
bacteriaEvaluation the economic importance of
bacteria
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The ProkaryotesInclude eubacteria and archaeabacteria,
which are fully functioning cellsA single spoonful of earth can contain >1000
prokaryotesRange in size from 1-10 µm in length and 0.7-
1.5 µm in width
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Prokaryote StructureCharacteristics:• Lack a membrane-bounded nucleus (DNA in
nucleoid region)• Outer cell wall containing peptidoglycan• Some move by means of flagella• Lack membranous organelles• May have accessory ring of DNA (plasmid)
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Reproduction in ProkaryotesAsexual
Prokaryotes reproduce asexually by means of binary fission
Methods of genetic recombinationConjugation
Sex pilus forms between two cellsDonor cell passes DNA to recipient cell through pilus
Transformation – taking up pieces of DNA secreted by live bacteria or released by dead bacteria
Transduction-transfer of portions of bacterial DNA from one cell to another
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Reproduction in ProkaryotesSome bacteria form resistant endospores
under unfavorable conditions
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Prokaryotic NutritionOxygen requirements:
Obligate aerobes – unable to grow in the absence of free oxygen
Obligate anaerobes – unable to grow in the presence of free oxygen
Facultative anaerobes – able to grow in either the presence or absence of free oxygen
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The Bacteria (eubacteria)Bacteria are commonly diagnosed using the
Gram stain procedureWhen washed after staining:
Gram-positive bacteria retain dye and appear purple
Gram-negative bacteria do not retain dye and appear pink
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The BacteriaStructure of cell wall also of diagnostic useBacteria can be further classified in terms of
their three basic shapesSpiral (spirilli),Rod (bacilli), andRound (cocci)
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CyanobacteriaFormerly called the Blue-Green algae
(Cyanophyta)Cyanobacteria are Gram-negative bacteria
that photosynthesize*Believed to be responsible for introducing
oxygen into the primitive atmosphereLack visible means of locomotionCan live in extreme environmentsWhen commensals with fungi, form lichens
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The ArchaeaArchaea were earlier considered bacteria their rRNA differs from BacteriaOther differences:
cell walls
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Archaea Metabolism• Most are chemoautotrophs• Some mutualistic• Some commensalistic• None known to be parasitic• None are photosynthetic• Many live in harsh conditions
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Many live in harsh conditions:Anaerobic marshes
MethanogensProduce methane from hydrogen gas and
carbon dioxideSalty lakes
HalophilesRequire high salt concentrations for growth
Types of Archaea
Hot sulfur springsThermoacidophilesReduce sulfides and survive best at
temperatures above 80ºCPlasma membranes contain unusual lipids
convey tolerance of high temperatures
Other Facts about bacteriacan cause disease
(Pneumonia, Strep. throat, TB, food poisoning, syphilis, gonorrhea…)
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Control of harmful bacteriasome can be destroyed or growth slowed with high temps, chemicals, steam, cold, antisepticssterilization, sanitation, pasteurization
Bacteria can be beneficialDecomposition or recycling of nutrients
Digestion (vitamins)make breads, beers, and wineantibiotics food texture (yogurt, cheeses)genetic engineering – insulinNitrogen fixation
Borrelia burgdorferiStaphylococcus