The World of Microbes:The World of Microbes:Viruses & BacteriaViruses & Bacteria

AP BiologyAP Biology

Chapter 23Chapter 23

Microbes are…Microbes are…

VirusesViruses BacteriaBacteria

Protists Protists

MicrobiologyMicrobiology is the study of is the study of microbes!microbes!

Small is Relative!Small is Relative!

11µµmm

Eukaryotic CellsEukaryotic Cells(10-100 (10-100 µµm)m)

Prokaryotic CellsProkaryotic Cells(0.2-10 (0.2-10 µµm)m)

StaphylococcusStaphylococcus

CyanobacteriumCyanobacterium

Escheria coliEscheria coli

VirusesViruses(0.05-0.2 (0.05-0.2 µµm)m)

VirusesViruses

VirusesViruses• DNA or RNA surrounded by a protein coatDNA or RNA surrounded by a protein coat• Parasitic - require a host cell (like cells of your Parasitic - require a host cell (like cells of your

body) to replicatebody) to replicate• Infect all kinds of organisms:Infect all kinds of organisms:

BacteriaBacteria Plant cellsPlant cells Animal cellsAnimal cells

• Some viruses only affect certain parts of their Some viruses only affect certain parts of their hosts hosts ex. Rabies affects nervous systemex. Rabies affects nervous system

VirusesViruses

Are Viruses Alive?Are Viruses Alive?

Viruses are not regarded as living Viruses are not regarded as living organisms; lack some attributes of life.organisms; lack some attributes of life.

• Are infectious particles, Are infectious particles, incapableincapable of of replicating independently.replicating independently.

• Lack cellular organization and Lack cellular organization and metabolism.metabolism.

VirusesViruses

ReplicationReplication• Viruses reproduce only inside living Viruses reproduce only inside living

cells.cells.• Viruses replicate by infecting Viruses replicate by infecting

susceptible cells and using the cell susceptible cells and using the cell to make more viruses.to make more viruses.

VirusesViruses

Various illnesses:Various illnesses: flu, AIDS, common coldflu, AIDS, common cold

Some antiviral medicinesSome antiviral medicines Evolve very, very, rapidlyEvolve very, very, rapidly

Makes effective treatment difficultMakes effective treatment difficult Each virus has a host rangeEach virus has a host range

A limited number of host cells that A limited number of host cells that it can infectit can infect

Virus ShapeVirus Shape

Viral shape is determined by the nature of Viral shape is determined by the nature of the virus’s protein coat. the virus’s protein coat.

Viruses such as the rabies and herpes Viruses such as the rabies and herpes viruses are surrounded by an extra viruses are surrounded by an extra envelope derived from membranes of the envelope derived from membranes of the host cell.host cell.

Viruses Come in Many ShapesViruses Come in Many Shapes

RabiesRabiesRabiesRabies

MeaslesMeaslesMeaslesMeasles

BacteriophageBacteriophageBacteriophageBacteriophage

HerpesHerpesHerpesHerpes

TobaccoTobaccoMosaicMosaic

TobaccoTobaccoMosaicMosaic

Viruses infect bacteriaViruses infect bacteria

BacteriophagesBacteriophages

Viruses called bacteriophagesViruses called bacteriophages• Can infect and set in motion a genetic Can infect and set in motion a genetic

takeover of bacteria, such as takeover of bacteria, such as Escherichia coliEscherichia coli

Bacteriophages Infect BacteriaBacteriophages Infect Bacteria

BacteriumBacterium

Newly formingNewly formingbacteriophagesbacteriophages

In this electron micrograph, In this electron micrograph, bacteriophages are seen attacking a bacteriophages are seen attacking a bacterium. bacterium.

They have injected their genetic material They have injected their genetic material inside, leaving their protein coats clinging inside, leaving their protein coats clinging to the bacterial cell wall. to the bacterial cell wall.

The black objects inside the bacterium are The black objects inside the bacterium are newly forming viruses.newly forming viruses.

Viral Structure -Viral Structure -EnvelopeEnvelope

(lipid bilayer)(lipid bilayer)EnvelopeEnvelope

(lipid bilayer)(lipid bilayer)

ProteinProteinCoatCoat

ProteinProteinCoatCoat

CoreCoreProteinsProteins

CoreCoreProteinsProteins

ReverseReverseTranscriptaseTranscriptase

ReverseReverseTranscriptaseTranscriptase

Genetic MaterialGenetic Material2 RNA molecules2 RNA moleculesGenetic MaterialGenetic Material2 RNA molecules2 RNA molecules

ReceptorReceptorReceptorReceptor

HIVHIVHIVHIV

Cross section of the virus that Cross section of the virus that causes AIDScauses AIDS

Inside is genetic material surrounded by a Inside is genetic material surrounded by a protein coat and molecules of reverse protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template transcription of DNA from the viral RNA template after the virus enters the host cell. after the virus enters the host cell.

HIV is among those that also have an outer HIV is among those that also have an outer envelope that is formed from the host cell’s envelope that is formed from the host cell’s plasma membrane. Spikes made of glycoprotein plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the (protein and carbohydrate) project from the envelope and help the virus attach to its host envelope and help the virus attach to its host cell. cell.

Herpes VirusHerpes Virus

Herpes VirusesHerpes Viruses

EnvelopeEnvelope(lipid bilayer)(lipid bilayer)

EnvelopeEnvelope(lipid bilayer)(lipid bilayer)

ProteinProteinCoatCoat

ProteinProteinCoatCoat

Viral DNA inViral DNA inprotein coatprotein coatViral DNA inViral DNA inprotein coatprotein coat

How Viruses Replicate: Herpes How Viruses Replicate: Herpes

(cytoplasm)

envelopecoat

DNA

nucleus

DNA

mRNA

1. Virus enters cell by endocytosis 3. Viral DNA transcribed to mRNA,

which moves to cytoplasm

2a. Viral envelope merges with nuclear membrane

2b.Protein coat disintegrates; viral DNA copied & enters nucleus

How Viruses Replicate: HerpesHow Viruses Replicate: Herpes

nucleus

mRNA

(cytoplasm)

envelopecoat

DNA DNA

mRNA

4. MRNA makes proteins, which enter nucleus

5.New viruses assembled & bud from nucleus, get envelope from inner nuclear membrane

6.Newly formed viruses leave the cell by exocytosis

Herpes VirusHerpes Virus Viruses such as the herpes virus can remain Viruses such as the herpes virus can remain

hidden in the cell for a long time without hidden in the cell for a long time without reproducing.reproducing.• Ex. Herpes virus that causes cold soresEx. Herpes virus that causes cold sores

No symptoms appear until something causes the No symptoms appear until something causes the virus to be active, virus to be active, • such as a fever or sunburn.such as a fever or sunburn.

As long as the virus does not reproduce, there As long as the virus does not reproduce, there are no symptoms.are no symptoms.

When the virus reproduces again, the cold sores When the virus reproduces again, the cold sores reappear.reappear.

VirusesViruses Diseases caused by viruses are hard to Diseases caused by viruses are hard to

treat or cure.treat or cure. There are no known drugs to destroy There are no known drugs to destroy

viruses, although some may be effective in viruses, although some may be effective in temporarily treating them.temporarily treating them.

The white blood cells of the Immune The white blood cells of the Immune System may surround a destroy a virus.System may surround a destroy a virus.

Antibodies may help destroy viruses.Antibodies may help destroy viruses.• Antibodies only act on one specific kind of Antibodies only act on one specific kind of

virus.virus.

VirusesViruses VaccinesVaccines

• Harmless substances made from weakened Harmless substances made from weakened or dead virusesor dead viruses

• Stimulate the immune system to create Stimulate the immune system to create defenses (antibodies) against the actual defenses (antibodies) against the actual pathogenpathogen

• Can prevent certain viral illnessesCan prevent certain viral illnesses Examples: chicken pox, flu, measles, Examples: chicken pox, flu, measles,

mumps, rubella, hepatitismumps, rubella, hepatitis

Prokaryotes:Prokaryotes:

Archaea & BacteriaArchaea & Bacteria

The Tree of LifeThe Tree of Life

All living things All living things classified in three classified in three domains:domains:

• BacteriaBacteria• ArchaeaArchaea• EukaryaEukarya

All living things All living things classified in three classified in three domains:domains:

• BacteriaBacteria• ArchaeaArchaea• EukaryaEukarya

Amazing Living ThingsAmazing Living Things Microbes indispensable to life: Microbes indispensable to life: Produce much of Earth’s:Produce much of Earth’s:

OxygenOxygen DecompositionDecomposition Over half of Earth’s biomassOver half of Earth’s biomass

More bacterial cells than human cells in More bacterial cells than human cells in your body!your body!

ProkaryotesProkaryotes Prokaryotes have:Prokaryotes have:

• Circular DNA, RNA, ribosomes, cytoplasm, Circular DNA, RNA, ribosomes, cytoplasm, plasma membraneplasma membrane

• Most prokaryotes have a cell wall, a capsule Most prokaryotes have a cell wall, a capsule (around the cell wall) and a flagellum (around the cell wall) and a flagellum

Prokaryotes Prokaryotes don’tdon’t have: have:• Organelles such as nucleus, chloroplasts, Organelles such as nucleus, chloroplasts,

mitochondria.mitochondria.

Generalized ProkaryoteGeneralized Prokaryote

CapsuleCapsule

Cell WallCell WallPlasmaPlasmaMembraneMembrane

CytosolCytosol

Nucleoid DNANucleoid DNA

FlagellumFlagellum

Plasmid DNAPlasmid DNA

Prokaryotic DNAProkaryotic DNA

The area that contains the genetic material The area that contains the genetic material is referred to as the is referred to as the nucleoidnucleoid. .

The genes are usually in one continuous The genes are usually in one continuous circular loop of DNA.circular loop of DNA.

There may be other small circles of DNA There may be other small circles of DNA outside the nulceoid called outside the nulceoid called plasmidsplasmids..

Bacteria/ArchaeaBacteria/Archaea Habitats (name a place, and they live Habitats (name a place, and they live

there!)there!)• They are specialistsThey are specialists

human skin, mouth, respiratory tract, large human skin, mouth, respiratory tract, large intestine, urogenital tract, etc.intestine, urogenital tract, etc.

salty Dead Seasalty Dead Sea extreme pHextreme pH archea in deep sea vents: 90-106archea in deep sea vents: 90-106o o CC

• Aerobes and anaerobesAerobes and anaerobes

Some Prokaryotes Thrive in Extreme Some Prokaryotes Thrive in Extreme ConditionsConditions

Cyanobacteria in Yellowstone Cyanobacteria in Yellowstone Hot SpringsHot Springs

Cyanobacteria in Yellowstone Cyanobacteria in Yellowstone Hot SpringsHot Springs

ArchaeaArchaea Unique lipid membranes, cell walls, and Unique lipid membranes, cell walls, and

rRNArRNA MethanogensMethanogens

• Convert COConvert CO22 to methane to methane

• Swamps, hot springs, vent communities, cow Swamps, hot springs, vent communities, cow stomachsstomachs

Halophiles - survive concentrated salt Halophiles - survive concentrated salt environmentenvironment

Thermoacidophiles - thrive in hot, acidic Thermoacidophiles - thrive in hot, acidic environmentenvironment

Generally in EXTREME environmentsGenerally in EXTREME environments

BacteriaBacteria

Evolve RapidlyEvolve Rapidly Most of the time are asexualMost of the time are asexual

Classified by shape, locomotion, pigments, Classified by shape, locomotion, pigments, nutrients, nutrients, coloniescolonies

BacteriaBacteria

Shape:Shape:• Cocci - roundCocci - round

• Bacilli - rodBacilli - rod

• Spirilla - spiralsSpirilla - spirals

Three Common Bacterial ShapesThree Common Bacterial Shapes

(a)(a)(a)(a) (b)(b)(b)(b)

(c)(c)(c)(c)

coccicoccicoccicocci

spirillusspirillusspirillusspirillus

bacillusbacillusbacillusbacillus

The Prokaryote FlagellumThe Prokaryote Flagellum

BacteriumBacteriumBacteriumBacterium

FlagellaFlagellaFlagellaFlagella

BacteriaBacteria

ReproductionReproduction

Reproduction is asexual, by simple Reproduction is asexual, by simple splitting (binary fission)splitting (binary fission)

Daughter cells are genetic clones of Daughter cells are genetic clones of the parent cellthe parent cell

Binary FissionBinary Fission

DNADNADNADNA

Bacteria - ReproductionBacteria - Reproduction

Binary fission:Binary fission:

• Very fast, up to once every 20 minutesVery fast, up to once every 20 minutes

• One bacterium-> 10One bacterium-> 102121 in 24 hours. in 24 hours.

ConjugationConjugation: (sexual reproduction): (sexual reproduction)

• Used only occasionally.Used only occasionally.

Bacteria – Sexual ReproductionBacteria – Sexual Reproduction

Conjugation:Conjugation:• Genetic variation through pili (structures Genetic variation through pili (structures

similar to flagella) and plasmid DNAsimilar to flagella) and plasmid DNA• DNA is exchanged between bacterial DNA is exchanged between bacterial

cellscells• Occurs through a special large, hollow Occurs through a special large, hollow

piluspilus• One bacterium acts as a donor, One bacterium acts as a donor,

transferring DNA to the recipient.transferring DNA to the recipient.

ConjugationConjugation

Sex PilusSex PilusSex PilusSex Pilus

DonorDonorDonorDonor

RecipientRecipientRecipientRecipient

Benefits of BacteriaBenefits of Bacteria

Symbiosis (mutualism) Symbiosis (mutualism) • Ruminants’ digestive tractsRuminants’ digestive tracts• Nitrogen fixing in soil, nodules on certain Nitrogen fixing in soil, nodules on certain

legumeslegumes• Bacteria on/in the human body: intestines and Bacteria on/in the human body: intestines and

vitamin K and B12vitamin K and B12 Biodegradation - oilBiodegradation - oil Food production - cheese, yogurt, Food production - cheese, yogurt,

sauerkrautsauerkraut DecomposersDecomposers

Our Relationship With BacteriaOur Relationship With Bacteria

Bacterial PathogensBacterial Pathogens Some cause disease = Some cause disease = pathogenicpathogenic In humans:In humans:

• Strep throatStrep throat• Toxins - tetanus, botulismToxins - tetanus, botulism• Pneumonia Pneumonia • "Flesh-eating" bacteria"Flesh-eating" bacteria• PlaguePlague• TuberculosisTuberculosis• Cholera Cholera • Lyme diseaseLyme disease

ANTIBIOTICS= anti bacterial!!!ANTIBIOTICS= anti bacterial!!!

The Causes of Tooth DecayThe Causes of Tooth Decay

Transmission of Bacterial Transmission of Bacterial PathogensPathogens

AirborneAirborne Water Water FoodFood Direct (skin contact, blood, and other Direct (skin contact, blood, and other

body fluids)body fluids) Insect vectors and other hosts such Insect vectors and other hosts such

as deer tick (Lyme) or mosquito.as deer tick (Lyme) or mosquito.

Germ Theory of DiseaseGerm Theory of Disease

Theory that microorganisms are the Theory that microorganisms are the cause of disease. cause of disease.

1859 – Louis Pasteur 1859 – Louis Pasteur • Credited with the idea that human Credited with the idea that human

diseases were caused by bacteria and diseases were caused by bacteria and viruses (germ theory)viruses (germ theory)

• Very important discovery in the field of Very important discovery in the field of medicinemedicine

• Also created vaccinations to prevent Also created vaccinations to prevent diseasedisease

Infectious DiseasesInfectious Diseases

Average age of death, in first world Average age of death, in first world countries, jumped 30+ years in last countries, jumped 30+ years in last century due to antibiotics, and enhanced century due to antibiotics, and enhanced hygiene and nutrition.hygiene and nutrition.

Antibiotic-resistant infections on the rise in Antibiotic-resistant infections on the rise in hospitals in the U.S.hospitals in the U.S.• This is due to bacterial evolution in response This is due to bacterial evolution in response

to widespread use of antibiotics!to widespread use of antibiotics!