CH 4 PROCARYOTES: BACTERIA CH 4 PROCARYOTES: BACTERIA

& ARCHAEA& ARCHAEA (“ARCHEAH”)(“ARCHEAH”)

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 & Bacterial Shapes, Arrangements & SizesSizes

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

PleomorphismPleomorphism

Same species varying Same species varying in shape and size due in shape and size due to variations in cell to variations in cell wall caused by wall caused by nutritional or nutritional or hereditary 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 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 Common, but not in all speciesCommon, but not in all species 2 major groups:2 major groups: Motility: flagellaMotility: flagella For attachment: fimbria and For attachment: fimbria and

pilipili FLAGELLA– self-propulsion, FLAGELLA– self-propulsion,

made of 3 distinct partsmade of 3 distinct parts Filament—helical structure Filament—helical structure

composed of proteins, 20 nm in composed of proteins, 20 nm in diameter, 1-70 nm in lengthdiameter, 1-70 nm in length

Hook—curved and tubular, Hook—curved and tubular, holds the filament, anchored to holds the filament, anchored to the cell by the…the cell by the…

Basal body—stack of rings that Basal body—stack of rings that go thru the cell wall to the cell go thru the cell wall to the cell membranemembrane

This arrangement allows the This arrangement allows the hook and filament to rotate hook and filament to rotate 360360° in a counter clockwise ° in a counter clockwise motion, which moves the motion, which moves the bacteria forwardbacteria forward

Flagella, cont.

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 Bacteria with flagella are sensitive to their sensitive to their

environmentenvironment

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 Appendages for Attachment & MatingAttachment & Mating

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