Download Prokaryotic Cell Structure

Prokaryotic Cell Structure
Bacterial Envelope
 comprises the inner cell membrane and
the cell wall
 if present, may have an outer membrane
such as in gram-negative bacteria
 May also be comprised of a capsule
Capsule or Slime Layer
 Made of polysaccharides (dextran, levan, cellulose)
 Outer part of cell envelope
 Not easily washed off (slime)
 Indicates virulence of organism
 Cannot be stained (must stain background)
 Helps them attach to other surfaces
 Prevents phagocytosis
Capsules
 Not all organism have capsules (nonencapsulated)
 On agar, encapsulated is smooth, glistening, and
mucoid
 On agar, non-encapsulated is dry and rough
 Variation on capsule is glycocalyx
Cell Wall
 Gram Positive- thicker than gram negative because of
peptidoglycan with amino acid bridges (NAG and NAM)
to make interconnected mesh-like molecule; also has
teichoic acids
 Gram Negative- peptidoglycan layer (inner wall)
covered with lipoproteins
Cytoplasmic Membrane
 The bacterial cytoplasmic membrane is a fluid
phospholipid bilayer that encloses the bacterial
cytoplasm.
 Inward folding are called mesosomes- part of electron
transport system; especially present during cell division
 Mesosomes not found in gram-negative bacteria
Nucleoid and Pasmids
 DNA not bounded by nuclear membrane
 Bacteria chromosome made from single strand DNA
 Coiled around RNA core
 Plasmids are found in some bacteria
 Considered extrachromosomal DNA
 Can transfer genetic information in process called
conjugation
Flagella
 Threadlike extensions
 Four groups
 Monotrichous- single plar
 Amphitrichous- both ends
 Lophotrichous- tuft of flagella
 Peritrichous-flagella over entire surface area
 Made of protein flagellin
 Four groups
 Made of a hook and basal body
 Bacteria spins one way and flagella spins the other
way
Flagellum
Pili (Fimbriae)
 Pili (hair) and fimbriae (fringe) are shorter and thinner
than flagella
 Hair-like all over cell
 Fimbriae are like velcro so they can stick to things and
help form biofilm
 Pili are a bit longer and help to transfer genetic material
through conjugation over the pilus bridge
Pili and Conjugation
Endospore
 May lie dry and dormant for a while
 Germinate when conditions are right
 Sporogenesis when conditions are poor for bacteria
 Can be stained and seen with microscope