Transcript CH 4 PROKARYOTES

CH 4
PROCARYOTES: BACTERIA &
ARCHAEA (“ARCHEAH”)
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First cells were a type of archaea that
were possibly related to modern ones
that live on sulfur compounds in
geothermal ocean vents—very
adaptable cell structures
Under light microscopes bacteria
appear simple and w/o features—
electron scopes in the 40’s—50’s
proved otherwise
Found that bacteria had : appendages
(flagella, pili, fimbria)
Layers to their cell coverings
(glycocalyx, cell wall, cell membranes)
Objects (NOT organelles!) in their
cytoplasm (ribosomes, granules,
nucleiod, chromosome)
Bacterial Shapes, Arrangements & Sizes
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Even if found with another cell, each
bacterial cell is independent and
capable of carrying out all life
processes
SHAPES—determined by the cell wall
Coccus (cocci)—spherical, ball shaped,
but can also be bean shaped, oval or
“pointy”
Bacillus (bacilli)—cylindrical, rod
shaped, many variations according to
species
Spirillum/spirochete—spiral shaped
cylinder, 3 types:
Spirillum– rigid, corkscrew
Spirochete– flexible, spring-like
Vibrio– comma shaped cylinder
Pleomorphism
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Same species varying in
shape and size due to
variations in cell wall
caused by nutritional or
hereditary differences
Corynebacterium
diphtheriae are rod
shaped, but can also be
club shaped, swollen,
curved, filamentous or
round
Mycoplasmas lack cell
walls, so have extreme
shape variations
Arrangements
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Bacteria can be arranged
several ways (fig 4.25)
determined by how the cells
divide
Coccus can be in pairs: diplo
Chains : strepto
Tetrad: sarcina
Irreg. clusters: staphylo
Bacillus can be pairs or chains
Palisades: diplobacillus that
snap at hinge and fold back on
each other
Spirilla normally do not remain
attached after division
See fig 4.26 for size
comparison
Appendages
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Common, but not in all species
2 major groups:
Motility: flagella
For attachment: fimbria and pili
FLAGELLA– self-propulsion, made
of 3 distinct parts
Filament—helical structure
composed of proteins, 20 nm in
diameter, 1-70 nm in length
Hook—curved and tubular, holds
the filament, anchored to the cell
by the…
Basal body—stack of rings that go
thru the cell wall to the cell
membrane
This arrangement allows the hook
and filament to rotate 360° in a
counter clockwise motion, which
moves the bacteria forward
Flagella, cont.
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Arranged in 3 ways: polar—flagella
attached at 1 or both ends
Monotrichous—single flagellum
Lophotrichous—small bunches of
flagella at same site
Amphitrichous—flagella at both ends
Second arrangement: peritrichous
where the flagella are randomly
dispersed over the entire cell
Periplasmic flagella are those found in
the space between the cell wall and
cell membrane and causes the cell to
wiggle, twist and flex (spirochetes)
Can determine motility by:
Put sample INSIDE semisolid media—
rapid growth thru entire medium
indicates motility
Observe using a hanging drop slide
(fig 4.4)
Bacteria with flagella are
sensitive to their environment
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Positive chemotaxis—
movement toward a favorable
chemical stimulus (food)
Negative chemotaxis—
movement away from a
repellant compound
Phototaxis—movement in
response to light
Appendages for
Attachment & Mating
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Pilus and fimbria provide
adhesion, but not locomotion
Fimbria are shorter and more
numerous strands
Pilus are longer and sparser
Some pathogens use fimbria to
adhere to epithelial cells to cause
disease:
Gonococcus—gonorrhea in
genitourinary tract
E. coli—intestinal tract
Sex pilus is a special tubular
structure made of pilin (protein)
used in bacterial conjugation:
partial transfer of DNA thru this
cytoplasmic connection—only
occurs between Gram neg. cells
Conjugation does occur between
Gram pos. cells, but not with a sex
pilus