Viruses, Bacteria & Archaea Chapter 21. Viruses, Bacteria & Archaea OutlineViruses Structure Classification Reproduction Prokaryotes Structure

Viruses, Bacteria & Archaea

Chapter 21

Viruses, BacterViruses, Bacteria & Archaeaia & Archaea

OutlineOutline

VirusesViruses StructureStructure

ClassificationClassification

ReproductionReproduction

ProkaryotesProkaryotes StructureStructure


NutritionNutrition

BacteriaBacteria

ArchaeaArchaea


The VirusesThe VirusesViruses are noncellular and thus cannot be Viruses are noncellular and thus cannot be classified with cellular organismsclassified with cellular organisms

Generally smaller than 200 nm in diameterGenerally smaller than 200 nm in diameter

Each type has at least two partsEach type has at least two partsCapsid: Outer layer composed of protein Capsid: Outer layer composed of protein subunitssubunits

Some enveloped by membraneSome enveloped by membrane

Others “naked”Others “naked”

Nucleic acid core: DNA or RNANucleic acid core: DNA or RNA

Vary in shape from thread-like to Vary in shape from thread-like to polyhedralpolyhedral

4Viruses


Viral CategorizationViral Categorization

Classification is based on:Classification is based on:Type of nucleic acidType of nucleic acid

Size and shapeSize and shape

Presence / absence of outer envelopePresence / absence of outer envelope


Parasitic NatureParasitic Nature

Viruses are:Viruses are:Obligate intracellular parasitesObligate intracellular parasites

Cannot reproduce outside a living cellCannot reproduce outside a living cell

Can be cultured only inside living cellsCan be cultured only inside living cells

Chicken egg Chicken egg

Tissue cultureTissue culture

7“Growing” Viruses

Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe Bacteriophages:The Bacteriophages:


Bacteriophages – Viruses that infect Bacteriophages – Viruses that infect bacterial cellsbacterial cells

Portions of capsid adhere to specific Portions of capsid adhere to specific receptor on the host cellreceptor on the host cell

Viral nucleic acid enters the cellViral nucleic acid enters the cell

Once inside, the virus takes over Once inside, the virus takes over metabolic machinery of the host cellmetabolic machinery of the host cell

Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaBacteriophages:Bacteriophages:

The Lytic CycleThe Lytic Cycle

Lytic cycle may be divided into five Lytic cycle may be divided into five stages:stages:AttachmentAttachment

PenetrationPenetration

BiosynthesisBiosynthesis

MaturationMaturation

ReleaseRelease

Viruses, BacterViruses, Bacteria & Archaeaia & ArchaeaThe Bacteriophages:The Bacteriophages:

The Lysogenic CycleThe Lysogenic Cycle

Phage becomes a prophagePhage becomes a prophageBecomes integrated into the host Becomes integrated into the host genomegenome

Becomes latentBecomes latent

May later reenter the lytic cycleMay later reenter the lytic cycle

11Lytic and Lysogenic Cycles in Prokaryotes


Reproduction of Animal VirusesReproduction of Animal Viruses

Animal virus enters the host cellAnimal virus enters the host cell

Uncoating releases viral DNA or RNAUncoating releases viral DNA or RNABudding:Budding:

Viral particles released in a budViral particles released in a bud

Acquires a membranous envelopeAcquires a membranous envelope

Retroviruses (AIDS)Retroviruses (AIDS)

Contain reverse transcriptaseContain reverse transcriptase

Carries out RNA Carries out RNA cDNA reverse cDNA reverse transcriptiontranscription

cDNA becomes integrated into host DNAcDNA becomes integrated into host DNA

13Reproduction of the Retrovirus HIV-1


Viral InfectionsViral InfectionsViruses are best known for causing Viruses are best known for causing infectious diseases in plants and animalsinfectious diseases in plants and animals Herpes, HIV, cancerHerpes, HIV, cancer

Viruses lack metabolism; thus, antibiotics Viruses lack metabolism; thus, antibiotics have no effecthave no effect

ViroidsViroids

Naked strands of RNANaked strands of RNA

Many crop diseasesMany crop diseases

PrionsPrions

Protein molecules with contagious tertiary Protein molecules with contagious tertiary structurestructure

Some human and other animal diseases - Mad Some human and other animal diseases - Mad cow diseasecow disease


The ProkaryotesThe Prokaryotes

Include bacteria and archaea, which Include bacteria and archaea, which are fully functioning cellsare fully functioning cellsA single spoonful of earth can contain A single spoonful of earth can contain >1000 prokaryotes>1000 prokaryotes

Range in size from 1-10 Range in size from 1-10 µµm in length m in length and 0.7-1.5 and 0.7-1.5 µµm in widthm in width

16Pasteur’s Experiment

17Bacterial Structure


Prokaryote StructureProkaryote Structure

Lack a membrane-bounded nucleus Lack a membrane-bounded nucleus (DNA in nucleoid region)(DNA in nucleoid region)

Outer cell wall containing Outer cell wall containing peptidoglycanpeptidoglycan

Some move by means of flagellaSome move by means of flagella

Lack membranous organellesLack membranous organelles

May have accessory ring of DNA May have accessory ring of DNA (plasmid)(plasmid)

19Flagella


Reproduction in ProkaryotesReproduction in Prokaryotes

AsexualAsexualProkaryotes reproduce asexually by Prokaryotes reproduce asexually by means of binary fissionmeans of binary fission

Methods of genetic recombinationMethods of genetic recombinationConjugationConjugation

Sex pilus forms between two cellsSex pilus forms between two cells

Donor cell passes DNA to recipient cell Donor cell passes DNA to recipient cell through pilusthrough pilus

TransformationTransformation

TransductionTransduction

21Fimbriae and Sex Pilus

22Binary Fission


Reproduction in ProkaryotesReproduction in Prokaryotes

TransformationTransformationOccurs when bacterium picks up free Occurs when bacterium picks up free pieces of DNA from other prokaryotespieces of DNA from other prokaryotes

Becomes incorporated into genomeBecomes incorporated into genome

TransductionTransductionOccurs when bacteriophages carry Occurs when bacteriophages carry portions of bacterial DNA from one cell to portions of bacterial DNA from one cell to anotheranother

Serve as vectorsServe as vectors

Some bacteria form resistant endospores Some bacteria form resistant endospores under unfavorable conditionsunder unfavorable conditions

24The Endospore of Clostridium tetani


Prokaryotic NutritionProkaryotic Nutrition

Oxygen requirements:Oxygen requirements:Obligate aerobes – unable to grow in Obligate aerobes – unable to grow in the absence of free oxygenthe absence of free oxygen

Obligate anaerobes – unable to grow Obligate anaerobes – unable to grow in the presence of free oxygenin the presence of free oxygen

Facultative anaerobes – able to grow Facultative anaerobes – able to grow in either the presence or absence of in either the presence or absence of free oxygenfree oxygen


Autotrophic ProkaryotesAutotrophic Prokaryotes

PhotoautotrophsPhotoautotrophsUse solar energy to reduce carbon Use solar energy to reduce carbon dioxide to organic compoundsdioxide to organic compounds

PhotosyntheticPhotosynthetic

ChemoautotrophsChemoautotrophsOxidize inorganic compounds to obtain Oxidize inorganic compounds to obtain the necessary energythe necessary energy

Use it to reduce COUse it to reduce CO22 to an organic to an organic compoundcompound

ChemosyntheticChemosynthetic


Heterotrophic ProkaryotesHeterotrophic Prokaryotes

Most prokaryotes are chemoheterotrophs Most prokaryotes are chemoheterotrophs that take in organic nutrientsthat take in organic nutrientsAerobic saprotrophs decompose most Aerobic saprotrophs decompose most large organic molecules to smaller large organic molecules to smaller moleculesmolecules

Essential components of healthy Essential components of healthy ecosystemecosystem

May be free-living or symbioticMay be free-living or symbioticNitrogen fixationNitrogen fixation

CommensalismCommensalism

ParasitesParasites

28Nodules of a Legume


The BacteriaThe Bacteria

Bacteria are commonly diagnosed Bacteria are commonly diagnosed using the Gram stain procedureusing the Gram stain procedure

When washed after staining:When washed after staining:Gram-positive bacteria retain dye and Gram-positive bacteria retain dye and appear purpleappear purple

Gram-negative bacteria do not retain Gram-negative bacteria do not retain dye and appear pinkdye and appear pink


The BacteriaThe Bacteria

Structure of cell wall also of Structure of cell wall also of diagnostic usediagnostic use

Bacteria can be further classified in Bacteria can be further classified in terms of their three basic shapesterms of their three basic shapesSpiral (spirilli),Spiral (spirilli),

Rod (bacilli), andRod (bacilli), and

Round (cocci)Round (cocci)

31Diversity of Bacteria


CyanobacteriaCyanobacteria

Formerly called the Blue-Green algae Formerly called the Blue-Green algae (Cyanophyta)(Cyanophyta)

Cyanobacteria are Gram-negative Cyanobacteria are Gram-negative bacteria that photosynthesizebacteria that photosynthesize

Believed to be responsible for Believed to be responsible for introducing oxygen into the primitive introducing oxygen into the primitive atmosphereatmosphereLack visible means of locomotionLack visible means of locomotion

Can live in extreme environmentsCan live in extreme environments

When commensals with fungi, form When commensals with fungi, form lichenslichens

33Diversity Among the Cyanobacteria


The ArchaeaThe ArchaeaArchaea were earlier considered Archaea were earlier considered bacteriabacteria

Carl Woese discovered that the base Carl Woese discovered that the base sequence of their rRNA differs from sequence of their rRNA differs from BacteriaBacteria

Other differences:Other differences:Archaea do not have peptidoglycan in Archaea do not have peptidoglycan in their cell walls like the Bacteriatheir cell walls like the Bacteria

Archaea biochemical more like Eukarya Archaea biochemical more like Eukarya than Bacteriathan Bacteria

Archaea now thought to be more Archaea now thought to be more closely related to Eukarya than to closely related to Eukarya than to BacteriaBacteria


Archaea MetabolismArchaea Metabolism

Most are chemoautotrophsMost are chemoautotrophs

Some mutualisticSome mutualistic

Some commensalisticSome commensalistic

None known to be parasiticNone known to be parasitic

None are photosyntheticNone are photosynthetic

Many live in harsh conditionsMany live in harsh conditions


Types of ArchaeaTypes of ArchaeaMany live in harsh conditions:Many live in harsh conditions:

Anaerobic marshesAnaerobic marshes MethanogensMethanogens Produce methane from hydrogen gas and Produce methane from hydrogen gas and carbon dioxidecarbon dioxide

Salty lakesSalty lakes HalophilesHalophiles Require high salt concentrations for growth, Require high salt concentrations for growth, andand

Hot sulfur springsHot sulfur springs ThermoacidophilesThermoacidophiles Reduce sulfides and survive best at Reduce sulfides and survive best at temperatures above 80ºCtemperatures above 80ºC

Plasma membranes contain unusual lipids Plasma membranes contain unusual lipids convey tolerance of high temperaturesconvey tolerance of high temperatures

37Thermoacidophile Habitat and Structure


ReviewReview

VirusesViruses StructureStructure

ClassificationClassification


ProkaryotesProkaryotes StructureStructure


NutritionNutrition

BacteriaBacteria

ArchaeaArchaea

Viruses, Bacteria & Archaea

Ending Slide Chapter 21

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Viruses, Bacteria & Archaea Chapter 21. Viruses, Bacteria & Archaea OutlineViruses Structure Classification Reproduction Prokaryotes Structure