Viruses and Prokaryotes

Viruses and ProkaryotesViruses and Prokaryotes

Chapter 24 Chapter 24

Learning Objective 1Learning Objective 1

• What is the structure of a What is the structure of a virusvirus??

• Contrast a virus with a living cellContrast a virus with a living cell

Virus (Virion)Virus (Virion)

• Subcellular particleSubcellular particle

• Consists ofConsists of• DNA or RNA genomeDNA or RNA genome• surrounded by protein coat surrounded by protein coat (capsid)(capsid)

Virus StructureVirus Structure

Fig. 24-1a, p. 502

RNA inside capsid

Capsid

0.1 µm

Fig. 24-1b, p. 502

Capsid with antenna-like fibers

DNA inside capsid

0.05 µm

Fig. 24-1c, p. 502

DNA inside capsid

CapsidTail

Tail fibers

Emerging DNA

0.1 µm

VirusesViruses

• Cannot metabolize on their ownCannot metabolize on their own

• Contain nucleic acids necessary to make Contain nucleic acids necessary to make copies of themselvescopies of themselves• but must invade and use metabolic machinery but must invade and use metabolic machinery

of living cells in order to reproduceof living cells in order to reproduce

KEY CONCEPTSKEY CONCEPTS

• A virus is a small particle consisting of a A virus is a small particle consisting of a DNA or RNA genome surrounded by a DNA or RNA genome surrounded by a protein coatprotein coat

Learn more about virus structure Learn more about virus structure by clicking on the figure in by clicking on the figure in

ThomsonNOW.ThomsonNOW.


• According to current hypotheses, what is According to current hypotheses, what is the evolutionary origin of viruses? the evolutionary origin of viruses?

Origin of VirusesOrigin of Viruses

• VirusesViruses may be bits of nucleic acid that may be bits of nucleic acid that originally “escaped” from animal, plant, or originally “escaped” from animal, plant, or bacterial cellsbacterial cells

HypothesisHypothesis

• Viruses must have evolved before the Viruses must have evolved before the three domains divergedthree domains diverged• It is unlikely that similar viruses that infect It is unlikely that similar viruses that infect

archaea and bacteria evolved twicearchaea and bacteria evolved twice


• Characterize Characterize bacteriophages (phages)bacteriophages (phages)• viruses that infect bacteriaviruses that infect bacteria

• What is the difference between a What is the difference between a lytic lytic cyclecycle and a and a lysogenic cyclelysogenic cycle??

Viral Reproductive CyclesViral Reproductive Cycles

• Lytic cycleLytic cycle• virus destroys host cellvirus destroys host cell

• Temperate virusesTemperate viruses

• do not always destroy their hostsdo not always destroy their hosts

• Lysogenic cycleLysogenic cycle• viral genome replicated along with host DNAviral genome replicated along with host DNA

Lytic CycleLytic Cycle

• 5 steps:5 steps:• attachmentattachment to host cell to host cell• penetrationpenetration of viral nucleic acid into host cell of viral nucleic acid into host cell • replicationreplication of viral nucleic acid of viral nucleic acid • assemblyassembly of components into new viruses of components into new viruses • releaserelease from host cell from host cell

Lytic CycleLytic Cycle

Fig. 24-2a (1), p. 504

Phages

Attachment. Phage attaches to cell surface of bacterium.

Bacterium

Bacterial DNA

Penetration. Phage DNA enters bacterial cell.

Phage protein

Replication and synthesis. Phage DNA is replicated. Phage proteins are synthesized.

Phage DNA

2

1

3

Fig. 24-2a (2), p. 504

Assembly. Phage components are assembled into new viruses.

Release. Bacterial cell lyses and releases many phages that can then infect other cells.

4

5

Fig. 24-2b, p. 504

0.25 µm

Lysogenic CycleLysogenic Cycle

• ProphageProphage • nucleic acid of phage becomes integrated into nucleic acid of phage becomes integrated into

bacterial DNAbacterial DNA

• Lysogenic cellsLysogenic cells • bacterial cells that carry prophagesbacterial cells that carry prophages

• Lysogenic conversionLysogenic conversion• bacterial cells containing certain temperate bacterial cells containing certain temperate

viruses exhibit new propertiesviruses exhibit new properties

Lysogenic CycleLysogenic Cycle

Fig. 24-3, p. 504

Attachment. Phage attaches to cell surface of bacterium.

1

2 Penetration. Phage DNA enters bacterial cell.

Prophage

3 Integration. Phage DNA integrates into bacterial DNA.

4 Replication. Integrated prophage replicates when bacterial DNA replicates.

These cells may exhibit new properties.


• Evolution occurs rapidly in prokaryotes; Evolution occurs rapidly in prokaryotes; natural selection acts on the genetic natural selection acts on the genetic variation provided by mutations and variation provided by mutations and genetic recombination and is facilitated by genetic recombination and is facilitated by rapid reproductionrapid reproduction

Insert “The two different Insert “The two different ways that viruses replicate ways that viruses replicate

(lytic and lysogenic cycles)”(lytic and lysogenic cycles)”

TbdTbd*suggested by Mary Durant, who will *suggested by Mary Durant, who will review existing animations currently review existing animations currently

slated for pickup (cd)slated for pickup (cd)

Watch the lytic and lysogenic Watch the lytic and lysogenic cycles by clicking on the figure cycles by clicking on the figure

in ThomsonNOW.in ThomsonNOW.


• Compare viral infection of animals and Compare viral infection of animals and plantsplants

• Identify specific diseases caused by Identify specific diseases caused by animal virusesanimal viruses

Animal VirusesAnimal Viruses

• Viruses enter animal cells by membrane Viruses enter animal cells by membrane fusion or endocytosis fusion or endocytosis

• Viral nucleic acid replicated in host cellViral nucleic acid replicated in host cell• proteins synthesizedproteins synthesized• new viruses assembled and released from cellnew viruses assembled and released from cell

Fig. 24-4b, p. 508

Envelope proteins 1 Virus attaches to specific receptors on plasma membrane of host cell.Envelope

CapsidNucleic acid

2 Membrane fusion. Viral envelope fuses with plasma membrane.

Receptors

Host-cell plasma membrane

3 Virus is released into host-cell cytoplasm.Capsid

Cytoplasm

NucleusNucleic acid

Viral nucleic acid separates from its capsid.

4

Ribo-somes 5 Viral nucleic acid

enters host-cell nucleus and replicates.ER

mRNA 6 Viral nucleic acid is transcribed into mRNA.

710 Viruses are

released from host cell.

Host ribosomes are directed by mRNA to synthesize viral proteins.

8 Vesicles transport glycoproteins to host-cell plasma membrane.

9 New viruses are assembled and enveloped by host-cell plasma membrane.

Membrane Membrane FusionFusion

Fig. 24-4c, p. 508

3 Endosomal vesicle forms and moves into cytoplasm.

Host-cell plasma membrane

4 Virus is released into host-cell cytoplasm.

2

Virus makes contact with plasma membrane of host cell.

1

Viral envelope fuses with host-cell plasma membrane (not shown).

5

Host-cell cytoplasm

Host-cell plasma membrane surrounds virus.

Endocytosis Endocytosis

Viral DiseasesViral Diseases

• DNA viruses causeDNA viruses cause• smallpox, herpes, respiratory infections, smallpox, herpes, respiratory infections,

gastrointestinal disordersgastrointestinal disorders

• RNA viruses causeRNA viruses cause• influenza, upper respiratory infections, AIDS, influenza, upper respiratory infections, AIDS,

some types of cancersome types of cancer

RubellaRubella

• An RNA virusAn RNA virus

Plant VirusesPlant Viruses

• Mostly RNA viruses Mostly RNA viruses

• Spread Spread amongamong plants by insect vectors plants by insect vectors

• Spread Spread throughthrough plant via plasmodesmata plant via plasmodesmata

Plant VirusesPlant Viruses


• Describe the reproductive cycle of a Describe the reproductive cycle of a retrovirusretrovirus, such as human , such as human immunodeficiency virus (HIV)immunodeficiency virus (HIV)

RetrovirusesRetroviruses

• Use Use reverse transcriptasereverse transcriptase

• Transcribe RNA genome into DNA Transcribe RNA genome into DNA intermediate intermediate • becomes integrated into host DNAbecomes integrated into host DNA

• Synthesize copies of viral RNASynthesize copies of viral RNA

HIVHIV

Fig. 24-5, p. 509

HIV Nucleic acid (RNA)

Envelope protein 1 HIV attaches to host-cell plasma membrane.Envelope

Capsid

Enzymes (reverse transcriptase, ribonuclease, integrase, protease)

2 HIV enters host-cell cytoplasm. CD4 Receptors

Viral nucleic acid (RNA)Reverse

transcriptase3 Capsid is removed by enzymes.

Reverse transcriptase catalyzes synthesis of single-stranded (ss) DNA that is complementary to viral RNA.

Host-cell plasma membrane Cytoplasm

ssDNA4 The DNA strand then serves as

template for synthesis of complementary DNA strand, resulting in double-stranded (ds) DNA.

NucleusdsDNA

Host chromosome

Viral RNA

dsDNA is transferred to host nucleus and enzyme integrase integrates DNA into host chromosome.

5

6 When activated, viral DNA uses host enzymes to transcribe viral RNA.

7 Viral RNA leaves nucleus, viral proteins are synthesized on host ribosomes, and virus is assembled.

8 Virus buds from host cell, using host-cell plasma membrane to make viral envelope.

Watch the HIV life cycle by Watch the HIV life cycle by clicking on the figure in clicking on the figure in

ThomsonNOWThomsonNOW


• What are What are viroidsviroids and and prionsprions??

ViroidsViroids andand PrionsPrions

• ViroidsViroids• short strands of RNA with no protein coatshort strands of RNA with no protein coat

• PrionsPrions• consists only of proteinconsists only of protein• cause cause transmissible spongiform transmissible spongiform

encephalopathies (TSEs)encephalopathies (TSEs)

PrionsPrions

Fig. 24-7, p. 511

Contacts

Prion Normal protein (PrP)

1 Prion induces normal PrP to misfold, forming another prion.

Contacts Contacts

2 Each prion can induce additional PrP proteins to misfold.

3 Proteins aggregate.


• Describe the structure and common Describe the structure and common shapes of prokaryotic cellsshapes of prokaryotic cells

Prokaryotic CellsProkaryotic Cells

• Do not have membrane-enclosed Do not have membrane-enclosed organellesorganelles• such as nuclei and mitochondriasuch as nuclei and mitochondria

Prokaryotic CellProkaryotic Cell

Fig. 24-9, p. 513

Outer membranePili (structures used for attachment)

Peptidoglycan layer

Cell wall

Nuclear area

(nucleoid)

Storage granule

Plasmid (DNA)Flagellum

Ribosomes

Bacterial chromosome (DNA)

Capsule

Plasma membrane

Bacterial ShapesBacterial Shapes

• Spherical Spherical (cocci)(cocci)


• Rod shaped Rod shaped (bacilli)(bacilli)


• Spiral Spiral • rigid helixrigid helix (spirillum) (spirillum) • flexible helix flexible helix (spirochete)(spirochete)

Bacteria StructureBacteria Structure

• Cell wallsCell walls composed of composed of peptidoglycanpeptidoglycan

• Some have Some have capsulecapsule surrounding cell wall surrounding cell wall

Bacterial Cell WallsBacterial Cell Walls

• Gram-positiveGram-positive bacteria bacteria• walls very thickwalls very thick• consist mainly of peptidoglycanconsist mainly of peptidoglycan

• Gram-negative Gram-negative bacteriabacteria• walls have thin peptidoglycan layerwalls have thin peptidoglycan layer• outer membrane (like plasma membrane)outer membrane (like plasma membrane)

Gram-NegativeGram-Negative Cell WallCell Wall

Gram-PositiveGram-Positive Cell WallCell Wall

Fig. 24-10a, p. 514

Cell wall

Thick peptidoglycan layer

Plasma membrane (inner membrane)

Transport protein

(a) Gram-positive cell wall.

Fig. 24-10b, p. 514

PolysaccharidesLipoprotein

Cell wall

Outer membrane

Thin peptidoglycan layer

Plasma membrane

Transport protein

(b) Gram-negative cell wall.

Bacterial PiliBacterial Pili

• Protein structures extending from cell Protein structures extending from cell • help bacteria adhere to one another or to help bacteria adhere to one another or to

other surfacesother surfaces

BacterialBacterial FlagellaFlagella

• Different from eukaryotic flagellaDifferent from eukaryotic flagella

• Consist ofConsist of• basal bodybasal body• hookhook• filament filament

• Produce rotary motionProduce rotary motion

BacterialBacterial FlagellaFlagella

Fig. 24-11b, p. 515

Plasma membrane

Peptidoglycan layer

CytoplasmOuter membrane

Protein ringsBasal

body

Hook

Filament

Learn more about the structure Learn more about the structure of prokaryotes and their cell of prokaryotes and their cell

walls by clicking on the figures walls by clicking on the figures in ThomsonNOWin ThomsonNOW


• Describe asexual reproduction in Describe asexual reproduction in prokaryotesprokaryotes

• Summarize three mechanisms Summarize three mechanisms ((transformationtransformation, , transductiontransduction, and , and conjugationconjugation) that may lead to genetic ) that may lead to genetic recombinationrecombination

Prokaryote GenesProkaryote Genes

• Genetic material consists ofGenetic material consists of• 1 circular DNA molecule1 circular DNA molecule• 1 or more 1 or more plasmids plasmids ((circular DNA fragments) circular DNA fragments)

Asexual ReproductionAsexual Reproduction

• Binary fissionBinary fission• cell divides, forming two cellscell divides, forming two cells

• BuddingBudding • bud forms, separates from mother cell bud forms, separates from mother cell

• FragmentationFragmentation • walls form inside cellwalls form inside cell• separates into several cellsseparates into several cells

Genetic Material ExchangeGenetic Material Exchange

• TransformationTransformation• bacterial cell takes in DNA fragments bacterial cell takes in DNA fragments

released by another cellreleased by another cell

• TransductionTransduction• phage carries bacterial DNA from one phage carries bacterial DNA from one

bacterial cell into another bacterial cell into another

• ConjugationConjugation• two cells of different mating types exchange two cells of different mating types exchange

genetic materialgenetic material

TransformationTransformation

Fig. 24-12, p. 515

1 Bacterium dies and releases DNA.

2 Fragments of foreign DNA bind to proteins on surface of living bacterium.

3 DNA enters cell, and some DNA is incorporated into host cell by reciprocal recombination.

DNA exchanged

TransductionTransduction

Fig. 24-13a, p. 516

1 DNA of a phage penetrates bacterial cell.

2 Phage DNA may become integrated with host-cell DNA as a prophage.

Phage DNA with bacterial genes

3 When the prophage becomes lytic, bacterial DNA is degraded and new phages are produced. New phages may contain some bacterial DNA.

Fragmented bacterial DNA

Fig. 24-13b, p. 516

4 Bacterial cell lyses and releases many phages, which can then infect other cells.

5 Phage infects new host cell.

6 Bacterial genes introduced into new host cell are integrated into host's DNA. They become a part of bacterial DNA and are replicated along with it.

Fig. 24-13b, p. 516

4 Bacterial cell lyses and releases many phages, which can then infect other cells.

5 Phage infects new host cell.

6

Bacterial genes introduced into new host cell are integrated into host's DNA. They become a part of bacterial DNA and are replicated along with it. Stepped Art

2 Phage DNA may become integrated with host-cell DNA as a prophage.Phage DNA with

bacterial genes3

Fragmented bacterial DNA

When the prophage becomes lytic, bacterial DNA is degraded and new phages are produced. New phages may contain some bacterial DNA.

1 DNA of a phage penetrates bacterial cell.

ConjugationConjugation

Fig. 24-14b, p. 517

F+ (donor) cell F– (recipient) cell

1 F+ (donor) cell produces sex pilus.

Bacterial chromosome

F plasmid

2 Sex pilus develops into conjugation bridge.

DNA replicates, and single strand of F plasmid DNA is transferred from F+ cell to F– cell.

3

Both bacterial cells now contain double-stranded F plasmid. The F– cell has been converted to an F+ cell.

4


• What are the modes of nutrition and What are the modes of nutrition and metabolic adaptations of prokaryotes?metabolic adaptations of prokaryotes?

Prokaryote NutritionProkaryote Nutrition

• Most are Most are heterotrophsheterotrophs• obtain energy and carbon from other obtain energy and carbon from other

organismsorganisms

• Some are Some are autotrophsautotrophs• make their own organic molecules from make their own organic molecules from

simple raw materialssimple raw materials

HeterotrophsHeterotrophs

• ChemoheterotrophsChemoheterotrophs • free-living free-living decomposersdecomposers• obtain carbon and energy from dead organic obtain carbon and energy from dead organic

mattermatter

• PhotoheterotrophsPhotoheterotrophs• obtain carbon from other organismsobtain carbon from other organisms• photosynthetic pigments trap light energyphotosynthetic pigments trap light energy

AutotrophsAutotrophs

• PhotoautotrophsPhotoautotrophs• obtain energy from sunlightobtain energy from sunlight

• ChemoautotrophsChemoautotrophs• obtain energy by oxidizing inorganic obtain energy by oxidizing inorganic

chemicals such as ammoniachemicals such as ammonia

Aerobes and AnaerobesAerobes and Anaerobes

• AerobicAerobic bacteria bacteria• require oxygen for cellular respirationrequire oxygen for cellular respiration

• Facultative anaerobesFacultative anaerobes • metabolize anaerobically when necessary metabolize anaerobically when necessary

• Obligate anaerobesObligate anaerobes• onlyonly metabolize anaerobically metabolize anaerobically


• Compare the three domains: Compare the three domains: ArchaeaArchaea, , BacteriaBacteria, and , and EukaryaEukarya

3 Domains3 Domains

• Domain Domain Archaea Archaea (prokaryotes)(prokaryotes)• cell walls have peptidoglycan cell walls have peptidoglycan

• Domain Domain Bacteria Bacteria (prokaryotes)(prokaryotes)• cell walls cell walls do notdo not have peptidoglycan have peptidoglycan

• Domain Domain EukaryaEukarya• four kingdoms of eukaryotesfour kingdoms of eukaryotes

3 Domains3 Domains

Fig. 24-16, p. 519

Domain Bacteria Domain Archaea Domain Eukarya

Proteobacteria

Alp

ha

Bet

a

Gam

ma

Del

ta

Ep

silo

n

Gra

m-p

osi

tive

s

Cya

no

bac

teri

a

Gra

m-p

osi

tive

s

Ch

lam

ydia

s

Sp

iro

chet

es

Ko

rarc

hae

ota

Eu

ryar

chae

ota

Cre

nar

chae

ota

Nan

oar

chae

ota

Eu

kary

ote

s

Common ancestor of all living organisms


• Distinguish among the main groups of Distinguish among the main groups of archaea based on their ecologyarchaea based on their ecology

• Identify the archaean phyla (Identify the archaean phyla (Table 24-3Table 24-3))

• Describe the main groups of bacteria Describe the main groups of bacteria ((Table 24-4Table 24-4) )

ArchaeaArchaea

• MethanogensMethanogens• produce methane from carbon compoundsproduce methane from carbon compounds• inhabit anaerobic environments inhabit anaerobic environments

• Extreme halophilesExtreme halophiles• inhabit saturated salt solutions inhabit saturated salt solutions

• Extreme thermophilesExtreme thermophiles• live at temperatures greater than 100live at temperatures greater than 100°° C C

Extreme HalophilesExtreme Halophiles

ArchaeansArchaeans

• CrenarchaeotaCrenarchaeota• EuryarchaeotaEuryarchaeota• NanoarchaeotaNanoarchaeota• KorarchaeotaKorarchaeota

ArchaeansArchaeans

BacteriaBacteria

• Gram-negativeGram-negative• ProteobacteriaProteobacteria• CyanobacteriaCyanobacteria• ChlamydiasChlamydias• SpirochetesSpirochetes

• Gram-positive bacteriaGram-positive bacteria

CyanobacteriumCyanobacterium

Fig. 24-18, p. 523

Heterocysts

50 µm


• Viroids and prions are smaller than virusesViroids and prions are smaller than viruses• A prion consists only of proteins A prion consists only of proteins • Unlike eukaryotic cells, prokaryotic cells Unlike eukaryotic cells, prokaryotic cells

do not have membrane-enclosed do not have membrane-enclosed organelles such as nuclei and organelles such as nuclei and mitochondriamitochondria

• Prokaryotes make up two of the three Prokaryotes make up two of the three domains: Bacteria and Archaeadomains: Bacteria and Archaea


• What are the ecological roles of What are the ecological roles of prokaryotes, their importance as prokaryotes, their importance as pathogens, and their commercial pathogens, and their commercial importance?importance?

Ecological Roles of ProkaryotesEcological Roles of Prokaryotes

• Essential Essential decomposersdecomposers • recycle nutrientsrecycle nutrients

• Some carry out Some carry out photosynthesisphotosynthesis

• Many are Many are symbioticsymbiotic with other organisms with other organisms

SymbiosisSymbiosis

• MutualismMutualism• both partners benefitboth partners benefit

• CommensalismCommensalism• 1 partner benefits1 partner benefits• other not harmed or helpedother not harmed or helped

• ParasitismParasitism• parasiteparasite benefits benefits• hosthost is harmed is harmed

Bacteria and DiseaseBacteria and Disease

• Pioneers in microbiologyPioneers in microbiology• Anton van LeeuwenhoekAnton van Leeuwenhoek• Louis PasteurLouis Pasteur• Robert KochRobert Koch

• Koch’s postulatesKoch’s postulates• guidelines to demonstrate specific guidelines to demonstrate specific pathogenpathogen

causes specific disease symptomscauses specific disease symptoms

Heliobacter Heliobacter pyloripylori

Fig. 24-19a, p. 525

Fig. 24-19b, p. 525

Pathogenic BacteriaPathogenic Bacteria

• ExotoxinsExotoxins • strong poisons released by pathogenic strong poisons released by pathogenic

bacteria bacteria

• EndotoxinsEndotoxins• poisonous components of cell wallspoisonous components of cell walls• released when bacteria diereleased when bacteria die

Pathogenic BacteriaPathogenic Bacteria

Antibiotic ResistanceAntibiotic Resistance

• Many bacteria have become resistant to Many bacteria have become resistant to antibioticsantibiotics

• R factorsR factors • plasmids with genes for antibiotic resistanceplasmids with genes for antibiotic resistance

Commercial ImportanceCommercial Importance

• Some bacteria produce antibiotics Some bacteria produce antibiotics

• Some bacteria used to produce cheeseSome bacteria used to produce cheese

• Lactic acid bacteria used in yogurt, Lactic acid bacteria used in yogurt, pickles, olives, sauerkrautpickles, olives, sauerkraut

Lactic Acid BacteriaLactic Acid Bacteria

Fig. 24-20, p. 526

5 µm


• Great diversity has evolved in the mode of Great diversity has evolved in the mode of nutrition, the metabolism, and the nutrition, the metabolism, and the ecological roles of prokaryotesecological roles of prokaryotes

Viruses and Prokaryotes

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