Prokaryotes
Prokaryotes
• The domain of Bacteria
– The typical bacterium contains: cytoplasm,
nuclear material, ribosomes, a cell wall,
plasma membrane, pili, flagellum, and
capsule.
Prokaryotes
• lack a cell nucleus, or any other
membrane-bound organelles
Prokaryotes
One way to classify
bacteria is by
examining its shape.
We will examine the
three basic shapes
but note that others
exist.
Prokaryotes
• Three basic shapes of bacteria
• Bacilli
• Cocci
are rod-shaped with noticeable breaks
spherically-shaped
• Spirilla
spiral-shaped with smooth curves
Prokaryotes
• Bacterial Colony
Morphology
study of the form and
structure
• Borrelia burgdorferi
• Spiral/Spirilla
• Lyme disease
Prokaryotes
• Form - What is the
basic shape of the
colony?
• For example, circular,
filamentous, etc.
• Escherichia coli
– Bacillus/Rod
Prokaryotes
•
Elevation - What is
the cross sectional
shape of the colony?
• Staphylococcus aureus
– Coccus- round
Prokaryotes
• In 1884 Hans Christian Gram developed a
staining procedure, Gram Staining
• The composition of the cell wall of
bacteria vary among species.
Prokaryotes
Prokaryotes
• Due to this difference
bacteria can be
divided into two
groups;
• Gram positive
• Gram negative
Prokaryotes
• Gram positive
– bacteria have thick
peptidoglycan cell walls
and retain a purple color
when stained with crystal
violet.
– Usually less toxic
Prokaryotes
• Gram negative
• bacteria have thin
peptidoglycan cell walls
these cells retain the red
color when stained
Prokaryotes
• Gram staining involves three processes:
1.Staining with a water-soluble dye called
crystal violet,
2.Decolorization,
3.Counterstaining, usually with safanin.
Results
• Red rods gram
negative
• Purple circles gram
positive
• Review…….
Prokaryotes
• Reagent: is a substance or compound consumed during a
chemical reaction.
•
•
•
•
•
Crystal violet (primary stain)
Iodine solution/Gram's Iodine ( fixes crystal violet to cell wall)
Decolorizer (e.g. ethanol)
Safranin (secondary stain)
Water (preferably in a squirt bottle)
Prokaryotes
• Decolorizer (e.g. ethanol) which dehydrates the peptidoglycan
layer, shrinking and tightening it.