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Bacterial Cell Structure (continued). You are here. Peptidoglycan structure. Bacteria typically face hypotonic environments Peptidoglycan provides support, Limits expansion of cell membrane Bacteria need other protection from hypertonic situations. Gram negative cell wall. Outer membrane.

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peptidoglycan structure
Peptidoglycan structure
  • Bacteria typically face hypotonic environments
  • Peptidoglycan provides support, Limits expansion of cell membrane
  • Bacteria need other protection from hypertonic situations
outer membrane
Outer membrane
  • Lipid bilayer membrane
    • Inner and outer leaflets
      • Inner leaflet made of phospholipids; outer leaflet is made of lipopolysaccharide (LPS)
      • LPS = endotoxin
    • Proteins for transport of substances
      • Porins: transmembrane proteins
    • Barrier to diffusion of various substances
  • Lipoprotein: anchors outer membrane to PG
structure of lps
Structure of LPS

extends from cell surface.

contains odd sugars

e.g. KDO.

Gln-P and fatty acids

take the place of

phospholipids. cell_envelope.htm

periplasmic space
Periplasmic Space theory.html

periplasmic space1
Periplasmic space:
  • A lot like cytoplasm, with
    • Peptidoglycan layer
    • Proteins that aid in transport
    • Proteins that break down molecules
    • Proteins that help in synthesis.
glycocalyx capsules and slime layers
Glycocalyx: capsules and slime layers

“Sugar covering”: capsules are firmly

attached, slime layers are loose.

Multiple advantages to cells:

prevent dehydration

absorb nutrients

protection from predators, WBCs

protection from biocides (as part of biofilms)

attachment to surfaces and site of attachment by others.

S-layers are highly structured protein layers that function like



capsule resources/visbulk.asp

fimbriae and pili
Fimbriae and pili

Both are appendages made of protein

Singular: fimbria, pilus

Both used for attachment

Fimbriae: to surfaces (incl. host cells) and other bacteria.

Pili: to other bacteria for exchanging DNA (“sex”). oralenv/images/sex1.jpg

  • Flagella: protein appendages for swimming through liquid or across wet surfaces.
  • Rotate like propellers.
  • Different from eukaryotic flagella.
  • Arrangements on cells:
  • polar,
  • Lophotrichous,
  • amphitrichous,
  • peritrichous. tk/ce/ introduction/bacteria.html

prokaryotic vs eukaryotic flagella
Prokaryotic vs. eukaryotic flagella
  • Prokaryotic flagella:
  • Made of protein subunits
  • Protrude through cell wall and cell membrane.
  • Stiff, twirl like a propeller
  • Eukaryotic flagella:
  • A bundle (9+2) of microtubules (made of protein)
  • Covered by cell membrane
  • Whipping action BIOL/Flagella.jpg gifs/flagella.gif


Bacteria change how they move in response to chemicals

Bacteria move toward attractants (e.g. nutrients).

Bacteria move away from repellants.

In this figure, bacteria use up nutrients in the agar, then move outward to where more nutrients are, producing rings of growth.

runs and tumbles bacteria find their way
Runs and Tumbles: bacteria find their way

spirochetes have internal flagella
Spirochetes have internal flagella
  • Axial filament: a bundle of internal flagella
    • Between cell membrane and outer membrane in spirochetes
    • Filament rotates, bacterium corkscrews through medium

Some bacteria move without flagella

  • Gliding
    • No visible structures, requires solid surface
    • Slime usually involved.
axial filaments
Axial filaments

gliding motility
Gliding Motility

Movement on a solid surface.

No visible organelles of locomotion.

Cells produce, move in slime trails.

Unrelated organism glide:

myxobacteria, flavobacteria,

cyanobacteria; appear to glide by

different mechanisms.

Cells glide in groups, singly, and

can reverse directions. myxobacteria/trails.jpg

from the membrane in the bacterial cytoplasm
From the membrane in: the bacterial cytoplasm
  • Cytoplasm is a gel made of water, salts, LMW molecules, and lots of proteins.
  • DNA = nucleoid, w/ proteins
  • Plasmids = small circular DNA
  • Ribosomes: site of protein synthesis.

Cytoplasm may also contain inclusions, gas vacuoles,

extended membrane systems, or magnetosomes.

But generally NO membrane-bound organelles.

inclusions and granules
Inclusions and granules
  • Storage molecules found as small bodies within cytoplasm.
  • Can be organic (e.g. PHB or glycogen) or inorganic (Sulfur, polyphosphate.
    • PHB, a type of PHA, degradable plastic (polyester); glycogen, a polymer of glucose.
    • Sulfur, a metabolic by-product; polyphosphate, polymer of PO4 phosphate_removal.htm


Membrane coated pieces of magnetite, assist bacteria in moving to microaerophilic environments. An organelle?

North is down.

Magnetospirillum magnetotacticum mtbphoto.html

how things get in and out of cells
How things get in (and out) of cells
  • Eukaryotic cells
    • Have transport proteins in membrane
    • Have a cytoskeleton made of microtubules
      • Allows for receptor mediated endocytosis, phagotcytosis, etc.
      • Cell membrane pinches in, creates vesicle
  • Prokaryotic cells
    • Have very little cytoskeleton
    • Can NOT carry out endocytosis
    • Entry of materials into cell by diffusion or transport processes ONLY.
illustrations entry into cells
Illustrations: entry into cells

Both prokaryotes and eukaryotes.

Only eukaryotes.

how molecules get through the membrane
How molecules get through the membrane

Small molecules like

gases can diffuse

through the bilayer.

Larger or more

hydrophilic molecules

require transport


Active transport


metabolic energy.

review of eukaryotic cells
Review of eukaryotic cells

Mitochondrion Plasmalemma (cell membrane)nucleus, ribosomeslysozomeendoplasmic reticulumgolgi body science/cell_biology.html