Prokaryotic
Cells
BACTERIA
The Prokaryotic Cell

Members of the prokaryotic world make up a vast
heterogeneous group of very small single-celled organisms.

Include bacteria and archae, although the majority are
bacteria

The thousands species of bacteria are differentiated by many
factors such as:

Morphology (shape), chemical composition (often detected by
staining reactions), nutritional requirements, biochemical activities,
and sources of energy (sunlight or chemicals)

These differences can only be seen with the use of a microscope
Size, Shape, and
Arrangement

Bacteria come in many sizes, and several shapes.


Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in length
Basic shapes include:

Cocci- round shaped

Bacillus- rod shaped

Spirillum- spiral shaped, helical shape like corkscrew, have rigid
bodies, and use flagella to move

Vibrio- curved

Spirochetes- helical and flexible, move by axial filaments found
within flexible external sheath

Square

Star
Cell Cluster Formation
Streptobacillus

Bacteria are also classified according to cell cluster
formation:
Cluster formation
Description
Diplococci
Two cocci cells paired
Staphylococci
Number of cells clustered
together (grape-like)
Streptococci &
Streptobacillus
Number of cells arranged
in a chain
Learning Check: What
Shape are these bacteria?
2.
1.
bacillus
spirillum
3.
coccus
6.
5.
vibrio
bacillus
spirochete
Shape and Arrangement

The shape of bacteria is determined by heredity.

Most bacteria are monomorphic: maintain a single shape


Environmental factors can alter that shape
Some bacteria like Rhizobium and Corynebacterium are
pleomorphic: can have many shapes, not just one.
Source for figure: http://textbookofbacteriology.net/Impact_2.html
Basic Components of Bacteria
*Cell wall- Most bacteria have a
cell wall but there are some that do
not like Mycoplasma species
Structures External to the Cell
Wall

Possible structures external to the prokaryotic cell
wall are:

Glycolax

Flagella

Axial filaments

Fimbrae

and Pili
What is the Glycocalyx?

Means sugar coat & is the general term used for
substances that surround cells

Bacterial glycocalyx is a viscous (sticky), gelatinous
polymer that is external to the cell wall

Composed of a polysaccharide, polypeptide, or both

Two types:
 Capsule:
substance is organized and is firmly
attached to the cell wall
 Slime
layer: substance is unorganized and only
loosely attached to the cell wall glycocalyx
Source for Fig. 1: http://emp.byui.edu/wellerg/The%20Cell%20Lab/Prokaryotic%20Cells/The%20Prokaryotic%20Cell.html
Fig. 1

(a) Micrograph of Streptococcus pneumoniae, the common cause of
pneumonia, showing a prominent capsule. (b) Bacteroides, a common
fecal bacterium, has a slime layer surrounding the cell
Learning Check

What advantage does a
glycocalyx provide a cell? (think
about its composition)
Glycocalyx

Very important component of biofilms
Fig. 2


Biofilms are densely packed communities of microbial
cells that grow on living or inert surfaces
A glycocalyx that helps cells in a biofilm attach to
their target environment and to each other is called
an extracellular polymeric substance (EPS)
 EPS
protects the cells within it
 Facilitates
communication among them
 and
enables the cells to survive by attaching to
various surfaces in their natural environment
Source for Fig. 2 http://www.microbiologybytes.com/blog/2010/09/08/the-biofilm-matrix/
Flagella


Some prokaryotes have flagella which are
long filamentous appendages that propel
bacteria

Peritrichous: flagella distributed over the entire
cell

Polar: at one or both poles or ends of the cell

Monotrichous: A single flagellum at one pole

Lopothrichous: a tuft of flagella coming from
one pole

Amphitrichous: flagella at both poles of the
cell
Bacteria that lack flagella re referred to as
atrichous (without projections)
Flagellar Movement
Figure 3.9 Motion of a peritrichous bacterium. In peritrichous bacteria,
runs occur when all of the flagella rotate counterclockwise and
become bundled. Tumbles occur when the flagella rotate clockwise,
become unbundled, and the cell spins randomly. In positive
chemotaxis (shown), runs last longer than tumbles, resulting in motion
toward the chemical attractant.
Axial Filaments

Spirochetes have unique structure and motility

Move my means of axial filaments
 Bundles
of fibrils that arise at the ends of the cell beneath
an outer sheath and spiral around the cell
 The
rotation of the filaments produces a movement of
the outer sheath that propels the spirochetes in a spiral
motion
Fimbriae and Pili

Many gram-negative bacteria contain hair-like appendages
that are shorter, straighter, and thinner than flagella

are used for attachment and transfer of DNA rather than for
motility

Fimbrae can occur at the poles of the bacterial cell or entire
surface of cell


Have a tendency to adhere to each other and to surfaces
Pili are usually longer than fimbrae but shorter than flagella and
are found as one or two per cell

Involved in motility and DNA transfer
Conjugation Pili
Learning Check

Several Escherichia coli cells are connected by
conjugation pili. How are pili different from bacterial
flagella?