Learning Goals

• Understand Which Organisms Are

Members of the Domains Archaea and

Bacteria?

• Learn how prokaryotes survive and

reproduce

• Understand how prokaryotes affect

humans and other eukaryotes

• Grasp what are viruses and the kinds of

viruses

Microorganisms

• Single-celled organisms that are too small

to be seen without a microscope

• Bacteria are the smallest living organisms

• Viruses are smaller but are not alive

Fig. 21-8b, p. 340

cytoplasm, with ribosomes

DNA, in

nucleoid region

pilus

bacterial

flagellum

outer capsule

cell wall

plasma

membrane

Ecological Importance of

Prokaryotes

• Decomposition

• Nitrogen fixation

• Mutualistic relationships

• Parasitic relationships

• Commercial uses

Treponema pallidum, a spiral-shaped bacteria which causes Syphilis in humans

Prokaryotes—characteristics

• Single-celled

• Metabolically diverse

• No nuclear

membrane

• Single chromosome

• No organelles

• Very small

• Cell wall

• Flagella rotate like

propellers

• Pili extend from the

cell surface for

adhesion or motion

Which Organisms Are Members of the

Domains Archaea and Bacteria?

– Earth’s first organisms were prokaryotes,

single-celled microbes that lacked organelles

– Prokaryotes are still abundant, forming two of

life’s three domains

• Bacteria

• Archaea

• Bacteria and Archaea are fundamentally

different

– They have some similarities

• They are both prokaryotic

• They are both single-celled organisms

EUBACTERIA (Bacteria)

ARCHAEBACTERIA (Archaea)

EUKARYOTES (Eukarya)

Differences between Bacteria and Archaea

– Structural and biochemical features

• Bacteria have peptidoglycan in their cell walls;

Archaea don’t

• There are also differences in the plasma

membrane composition, ribosomes, and RNA

polymerases between the two domains

• Differences in transcription and translation also

exist between the two

Bacteria

• Microscopic

• Unicellular

• Live in every habitat on the planet

• There are more bacterial cells on each of

our bodies than there are our cells of our

own

– important in skin, mouth, intestinal tract

Bacteria—what do they look

like?

Rods, spheres, spirals, vibrio

Bacterial Shapes

coccus bacillus

spirillum

p. 334

Bacteria

• All bacteria reproduce through asexual

reproduction (one parent) binary fission,

which results in cell division.

– Two identical clone daughter cells are

produced.

Fig. 21-5, p.335

Prokaryotic Fission

Bacterial Diversity

• Photoautotrophic

– Aerobic (Cyanobacteria)

– Anaerobic (Green bacteria)

• Chemoautotrophic

– Important in nitrogen cycle

• Chemoheterotrophic

– Largest group

Cyanobacteria

Fig. 19-6

• Bacteria, often in combination with yeasts

and molds, are used in the preparation of

fermented foods such as:

– cheese, pickles, soy sauce, sauerkraut,

vinegar, wine, and yogurt.

• Bacteria are also important to numerous

industrial processes,

– wastewater treatment

– industrial production of antibiotics and other

chemicals.

• Some bacteria act as pathogens

– tetanus, typhoid fever, pneumonia, syphilis,

cholera, food-borne illness, leprosy, and

tuberculosis(TB).

– In plants, bacteria cause leaf spot, fireblight,

and wilts.

– The mode of infection includes contact, air,

food, water, and insect-borne microorganisms

EUBACTERIA (Bacteria)

ARCHAEBACTERIA (Archaea)

EUKARYOTES (Eukarya)

Archaebacteria

Methanogens

Extreme halophiles

Extreme thermophiles

Fig. 21-11b, p.340

Methanogens

Fig. 21-12a, p.341

Extreme Halophiles

Fig. 21-12b, p.341

Extreme Thermophiles

Infectious Diseases

Salmonella Outbreak Sickens 172 in

18 States • U.S. health officials investigating latest bacterial

infection, possibly linked to tomatoes.

Ticks, small rodents, and other non-

human vertebrate animals all serve

as natural reservoirs for B. burdorferi.

This means that the Lyme disease

bacteria can live and grow within

these hosts without causing them to

die. Larvae and nymph ticks typically

become infected with the Lyme

disease spirochete, B. burgdorferi,

when they feed on small animals that

carry the bacteria in spring and

summer. The bacteria remain in a tick

as it changes from larva to nymph or

from nymph to adult in late summer or

early fall. Infected nymphs bite and

transmit B. burgdorferi bacteria to

other small rodents, mammals, and

humans, all in the course of their

normal feeding behavior.

Lyme disease

Diseases • Infection: invasion of the body by a pathogen.

• The outcome—disease—occurs when the

body’s defenses are overcome, at least

temporarily.

– Sporadic diseases (whooping cough) occur irregularly

among just a few people.

– Endemic diseases (tuberculosis) are present most of

the time but in limited populations.

– An epidemic results if the disease spreads throughout

the population, but for a limited time.

– A pandemic is defined as an outbreak in several

countries at the same time.

Diseases

• AIDS is a pandemic with no end in sight; SARS was a brief pandemic in 2003.

• Two barriers keep pathogens from achieving world dominance.

– The pathogen’s host has usually evolved immune defenses against it.

– If the pathogen kills too well and too fast, it might disappear.

The Threat of Drug-Resistance

• In a population of pathogens, drug-

resistant individuals survive and reproduce

– About half the known strains of Streptococcus

pneumoniae are penicillin resistant

– Many strains of HIV are now resistant to the

antiviral drugs used to fight them

Where Do Viruses Fit?

• Not “alive”?

• Not a cell

• Nucleic acids in protein shell

• Do not grow, do not maintain

homeostasis, and do not

metabolize on their own

• Use host cell to replicate

• Lytic and Lysogenic life cycles

Early Stage of Influenza Virus

Walking Dead Zombies

-caused by a virus

Viruses

• Chicken pox - varicella zoster virus Ebola

hemorrhagic fever - Ebola virus Hepatitis

HIV - human immunodeficiency virus

Influenza Measles - rubeola virus

Mononucleosis - Epstein-Barr virus

Mumps - mumps virus Polio Severe Acute

Respiratory Syndrome (SARS) Smallpox -

variola virus

Fig. 21-4, p. 337

Stepped Art

A2 Chromosome and integrated viral DNA are replicated. E Lysis of host cell

lets new virus particles

escape.

A Virus particle binds,

injects genetic material.

Lytic

Pathway

A1 Viral DNA is

inserted into host

chromosome by

viral enzyme

action.

Lysogenic

Pathway

D Accessory parts are

attached to viral coat. B Host replicates

viral genetic material,

builds viral proteins.

A3 Cell

divides;

recombinant

DNA in each

daughter cell.

C Viral proteins self-

assemble into a coat

around viral DNA.

A4 Viral

enzyme excises

viral DNA from

chromosome.

Fig. 21-5, p. 337

viral enzyme

(reverse transcriptase)

C Viral DNA gets

integrated into the

host’s chromosome.

D Viral DNA gets

transcribed along

with the host’s genes.

A Viral RNA

and protein

enter the

host cell.

E Some RNA

transcripts are

new viral RNA.

Others are

translated into

viral proteins.

RNA and

proteins

assemble as

new virus

particles.

viral coat

proteins

nucleus

B Viral reverse

transcriptase

uses viral RNA

to make double-

stranded viral

DNA.

viral proteins

viral RNA

viral DNA one of two

strands of

viral RNA

lipid envelope

with proteins F Viral particles

bud from the

infected cell.

What Are Viruses, Viroids, and

Prions? • Viral infections are difficult to treat

– Antibiotics against bacteria are infective

against viruses

– Antiviral drugs may also kill host cells

– Viruses “hide” within cells and are hard to

detect

– Many antiviral drugs destroy or block the

function of enzymes that targeted viruses

require for replication

What Are Viruses, Viroids, and

Prions? • Viral infections are difficult to treat

(continued)

– Viruses have high mutation rates because

they lack the mechanisms to correct errors

that occur during replication of their genomes

• Mutations can confer resistance to an antiviral drug

• Resistant viruses spread and multiply, rendering a

drug ineffective

• Some infectious agents are even simpler

than viruses

– Viroids are infectious particles with only short

RNA strands (no protein coat)

– These particles can enter a host cell nucleus

and direct new viroid synthesis

– A number of crop diseases are caused by

viroids, including cucumber pale fruit disease,

avocado sunblotch, and potato spindle tuber

disease

What Are Viruses, Viroids, and

Prions? • Some infectious agents are even simpler

than viruses (continued)

– Prions are even more puzzling than viroids

– A fatal degenerative disease called kuru was

discovered in a New Guinea tribe (the Fore) in

1950

– Kuru causes a loss of coordination, dementia,

and death

– Kuru in the Fore tribe was transmitted by ritual

cannibalism of the dead

Kuru Image

What Are Viruses, Viroids, and

Prions? • Some infectious agents are even simpler

than viruses (continued)

– It was noted that kuru resembled certain other

diseases

• Creutzfeldt-Jakob (disease CJD) in humans

• Scrapie in sheep

• Bovine spongiform encephalopathy (BSE, or “mad

cow disease”) in cattle

– These diseases create holes in brain tissue