DNA.html: 27_08ProkChromosome.jpg
A prokaryote such as this E. coli cell has a circular
chromosome consisting of a single ring of DNA, located in a nucleoid region.
Many cells also harbor smaller, non-genome rings of DNA called plasmids.
anabena.html: 27_10Anabena.jpg
Metabolic cooperation in a colonial prokaryote.
In the filamentous cyanobacterium Anabaena, cells known as heterocytes fix nitrogen,
while the other cells carry out photosynthesis, and these cells exchange metabolic products.
capsule.html: 27_04BacterialCapsule.jpg
The polysaccharide or protein capsule surrounding the cell wall of this Streptococcus
enables the bacterium to attach to cells that line the human respiratory tract,
such as a tonsil cell. Other prokaryotes stick to the substrate by
fimbriae.
cyanobacteria.html: 27_18lBacteriaCyano-L.jpg
Cyanobacteria ("Blue-green algae") are photosynthetic
and can form stromatolites.
These two species of Oscillatoria form a filamentous colony.
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Some filamentous colonies such as Anabaena
have cells specialized for nitrogen fixation.
domains.html: 27_T02DomainComparison-L.jpg
A comparison of the three domains of life.
Among the prokaryotes,
Aside from not having organelles such as the nucleus, and having circular DNA,
Archaea exhibit many traits not shared with Bacteria.
endospore.html: 27_09Endospore.jpg
An endospore.
Bacillus anthracis, the bacterium that causes anthrax, produces persistent endospores.
An endospore's thick, protective coat helps it survive in the soil for years.
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fimbriae.html: 27_05ProkFimbriae.jpg
Some prokaryotes attach to surfaces or to other prokaryotes via numerous protein appendages called
fimbriae.
flagellum.html: 27_06ProkFlagellum.jpg
Prokaryotic flagellum. Unlike an eukaryote
flagellum,
the motor of the prokaryotic flagellum is a basal apparatus embedded in the plasma membrane.
A curved hook turns in the basal apparatus, moving
the attached filament, which is composed of the protein flagellin.
This allows the cell to responding to a stimulus in a directional movement called taxis.
gram-positive.html: 27_13BacterialGramPos.jpg
| Gram-Positive Bacteria | Soil-dwelling Streptomyces are a source of many antibiotics, including streptomycin used to treat tuberculosis, which is caused by another gram-positive bacteriun, Mycobacterium tuberculosis | Mycoplasmas are tiny and have no cell walls. One species causes "walking pneumonia". Hundreds of mycoplasmas are seen here covering a human fibroblast cell. |
|---|
gram.html: 27_03GramStaining.jpg
| Bacteria are stained with a violet dye and iodine, rinsed in alcohol, and then stained with a red dye. | ||
|---|---|---|
| Gram-positive bacteria have a cell wall with a large amount of peptidoglycan that traps the violet dye in the cytoplasm, masking the added red dye. | Gram-negative bacteria have less peptidoglycan. The violet dye is easily rinsed from the cytoplasm, and the cell appears red after the red dye is added. | |
halophiles.html: 27_14ExtremeHalophiles.jpg
Extreme halophiles.
Colorful “salt–loving” archaea thrive in these ponds near San Francisco.
Used for commercial salt production, the ponds contain water that is five to six times as salty as seawater.
lyme.html: 27_16LymeDisease.jpg
Lyme disease.
Ticks in the genus Ixodes spread the disease by transmitting the spirochete Borrelia burgdorferi.
A large, ring–shaped rash may develop at the site of the tick's bite.
membranes.html: 27_07ProkMembranes.jpg
| Specialized membranes of prokaryotes. | ||
|---|---|---|
| Infoldings of the plasma membrane, reminiscent of the cristae of mitochondria, function in cellular respiration in some aerobic prokaryotes. | Photosynthetic prokaryotes called cyanobacteria have thylakoid membranes, much like those in chloroplasts. | |
methane.html: 27_sewtre.gif
phylogeny.html: 27_16ProkaryotePhylogeny-L.jpg
Prokaryotes do not constitute a monophyletic
clade.
Archaea are more closely related to Eukarya than to Bacteria.
plasmid.html: 27_plasmid.jpg
Some bacteria have small rings of non-genome DNA called plasmids.
prokaryote_wall.html: 27_03CellWall.jpg
Surrounding the plasma membrane, bacteria possess a cell wall
composed of varying amounts of peptidoglycan, a polymer made of amino acids and sugars.
proteobacteria.html: 27_E-coli.jpg
Escherichia coli is a proteobacterium in the Gram-negative group.
rhizobium.html: 27_13BacterialRhizobium.jpg
Rhizobium is another proteobacterium among the Gram-negative bacteria.
They live inside root cells of legumes (plants of the pea/bean family),
where the bacteria convert atmospheric nitrogen to organic compounds such as ammonia
in a process called nitrogen fixation.
shapes.html: 27_02ProkaryoteShapes.jpg
| Cocci (singular, coccus) are spherical prokaryotes. They occur singly, in pairs (diplococci), in chains (such as these streptococci), and in clusters like bunches of grapes (staphylococci). | Bacilli (singular, bacillus) are rod-shaped prokaryotes. They are usually solitary, sometimes the rods are arranged in chains (streptobacilli). | Spiral prokaryotes include spirilla, which range from comma-like shapes to long coils, and spirochetes (shown here), which are corkscrew-shaped. |
thermophiles.html: 27_01Thermophiles.jpg
Extreme thermophiles.
Orange and yellow colonies of “heat–loving” archaea
in the hot water of a Nevada geyser.