PROKARYOTE CELLS
Microbiology
Stephanie Lanoue
4-1 Understand prokaryotic cells
4-2 Identify shapes of bacteria
4-3 Describe the structure and function of the
glycocalyx.
4-4 Differentiate flagella, axial filaments, fimbriae
and pili
PROKARYOTIC OVERVIEW

Prokaryote comes from the Greek word for
“____nucleus”.
Review Question
Does a prokaryotic cell have a true membranebound nucleus?
STRUCTURE OF BACTERIAL CELLS

External Structure
Glycocalyx (sugar coat)
 Flagella
 Axial Filaments
 Fimbriae and Pili
 Cell Wall


Internal Structure (to the cell wall)





Cell membrane
Cytoplasm
Ribosome
Inclusions
Endospore
EXTERNAL STRUCTURE

Glycocalyx (______ coat)
Many prokaryotes secret it on their surface
 Viscous (________)
 Gelatinous polymer
 Composed of polysaccharide, polypeptide, or both

If it is organized and firmly attached to the cell wall
is Capsule
 If it is unorganized and loosely attached to the cell
wall is slime layer

EXTERNAL STRUCTURE
Glycocalyx
 Contribute to ______________

Capsules prevent phagocytosis
 Extracellular polymeric substance helps form
biofilms

EXTERNAL STRUCTURE (CONT’D)

Flagella (singular, flagellum)
Filamentous appendages external of the cell
 ________ bacteria
 Made of protein called flagellin

Three basic parts of flagellum
Filaments, long outermost region
Protein flagellin, arranged in several chains
Rotates for the movements
Hook, Basal body, anchor the flagellum to the cell wall and plasma
membrane
FIGURE 4.7 ARRANGEMENTS OF BACTERIAL FLAGELLA.
EXTERNAL STRUCTURE (CONT’D)


Mobility by Flagella
Chemotaxis, movement of bacteria _______ or ______ from
chemical

Directed movement, in response to a chemical
Movement to a chemical: chemical is a chemoattractant (e.g.
sugar, amino acid)

Movement away from chemical:
chemical is a chemorepellent
(toxic substance)
EXTERNAL STRUCTURE (CONT’D)


Fimbriae and Pili
_____________ appendages that allow for
attachment
 Mostly in gram-negative bacteria
 Shorter and thinner than flagella
 Composed of protein called pilin
Two types with different functions
1. Fimbriae




a few – hundreds
Main function is attachment, such as
forming biofilm
Neisseria gonorrhoeae, gonorrhea

Help the microbe colonize mucous membranes
CELL WALL
Responsible for _______ of cells
 __________ the cell membrane


Prevent from rupturing, when water pressure inside
is greater than outside
Point of anchorage for flagella
 Contributes to pathogenicity


Ability to cause disease, in some bacteria
FIGURE 4.6 THE STRUCTURE OF A PROKARYOTIC CELL.
Capsule Cell wall
Cytoplasm
70S Ribosomes
Plasma membrane
Cell wall
Nucleoid containing DNA
Capsule
Inclusions
CELL WALL

Peptidoglycan,


Polymer of a repeating disaccharide in
_______(Backbone ):
Rows are linked by polypeptides
BACTERIAL CELL WALLS

Gram Positive
______ peptidoglycan
 Additional components, anchor the layers together and
to plasma membrane

BACTERIAL CELL WALLS

Gram Negative
_______ peptidoglycan
 Additional outer membrane
made of polysaccharides,
lipoproteins, and
phospholipids

BACTERIAL CELL WALLS
Gram-Negative Cell Walls
 _________ from phagocytes and
antibiotics
 Made of lipopolysaccharide
(LPS)

CELL WALLS AND THE GRAM STAIN
MECHANISM

Crystal violet-iodine crystals form inside cell

Gram-positive


Alcohol dehydrates peptidoglycan
Gram-negative
Alcohol dissolves outer membrane and leaves holes in peptidoglycan
 CV-I washes out; cells are colorless
 Safranin added to stain cells

Prokaryote Plasma (Cytoplasmic)
Membrane
Phospholipid bilayer that _______ the cytoplasm
Peripheral proteins on the membrane surface
Integral and transmembrane proteins penetrate
the membrane
Lipid
bilayer of plasma
membrane
Peptidoglycan
Outer membrane
Plasma membrane of cell
FIGURE 4.14B PLASMA MEMBRANE.
Outside
Lipid
bilayer
Pore
Peripheral
protein
Polar head
Nonpolar
fatty acid
tails
Inside
Integral
proteins
Peripheral protein
Polar head
Lipid bilayer of plasma membrane
CELL MEMBRANE FUNCTION
Selective ____________
 Selectively permeable
 Proteins, channel, large molecule pass through
 Disinfectants and Antiseptics


many are aimed at disrupting the cell membrane

Alcohol and detergents
INTERNAL STRUCTURE

Cytoplasm

The substance ______ the plasma membrane

Contains:





80% water
Protien, enzymes
Lipids
Inorganic ions
Cytoskeleton
INTERNAL STRUCTURE


Bacterial chromosome: circular ______ of
DNA that contains the cell's genetic
information
Plasmids: extrachromosomal genetic
elements; carry non-crucial genes (e.g.,
antibiotic resistance, production of toxins)
INTERNAL STRUCTURE

Ribosomes
Sites of __________ synthesis
 Made of protein and ribosomal RNA

Some antibiotics are aimed at ribosomes of bacterial
cells
 Streptomycin, Neomycin, Erythromycin and
Tetracycline work by inhibiting protein synthesis by
disrupting ribosomes

INTERNAL STRUCTURE

Endospores, Gram + bacteria

Resting cells; produced when nutrients are depleted
___________ to desiccation, heat, chemicals, and
radiation
Produced by Bacillus and Clostridium
Sporulation: endospore formation
Germination: endospore returns to vegetative state

e.g. Clostridium sp. (clostridium tetani)




FIGURE 4.21B FORMATION OF ENDOSPORES BY SPORULATION.
Endospore
An endospore of Bacillus subtilis
FIGURE 4.21A FORMATION OF ENDOSPORES BY SPORULATION.
Cell wall
Cytoplasm
Spore septum begins to isolate
newly replicated DNA and a
small portion of cytoplasm.
Plasma membrane starts to surround DNA,
cytoplasm, and membrane isolated in step 1.
Plasma
membrane
Bacterial
chromosome
(DNA)
Sporulation, the process of endospore formation
Spore septum surrounds isolated portion,
forming forespore.
Two membranes
Peptidoglycan layer forms between membranes.
Endospore is freed from cell.
Spore coat forms.