Download Chapter 3

Prokaryotic Form and Function
Prokaryotic Profiles:
The Bacteria and Archaea
Chapter 3
• Prokaryotes can be distinguished from eukaryotes
by:
-  the way their DNA is packaged (lack of
nucleus and histones)
-  the makeup of their cell wall (peptidoglycan
and other unique chemicals)
-  their internal structure (lack of membranebounded organelles)
Copyright*©*The*McGraw3Hill*Companies,*Inc)*Permission*required*for*reproducAon*or*display.*
The Structure of the Prokaryotic Cell
The Structure of the Prokaryotic Cell
• All bacterial cells possess:
-  a cell membrane
• Some but not all bacterial cells possess:
-  flagella, pili, and fimbriae
-  cytoplasm
-  an outer membrane
-  ribosomes
-  plasmids
-  a cytoskeleton
-  inclusions
-  one (or a few) DNA chromosome(s)
-  endospores
• Most bacterial cells possess:
-  a cell wall
-  a surface coating called a glycocalyx
-  intracellular membranes
Prokaryotic Cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Prokaryotic Shapes and Arrangements
In All Bacteria
Cell (cytoplasmic) membrane—A thin sheet of lipid
and protein that surrounds the cytoplasm and controls
the flow of materials into and out of the cell pool.
Bacterial chromosome or nucleoid—Composed of
condensed DNA molecules. DNA directs all genetics
and heredity of the cell and codes for all proteins.
Ribosomes—Tiny particles
composed of protein and RNA
that are the sites of protein
synthesis.
In Some Bacteria
Fimbriae—Fine, hairlike
bristles extending from the
cell surface that help in
adhesion to other
cells and surfaces.
• Most prokaryotes exist as unicellular organisms
-  sometimes they can act as a group, in
colonies or in biofilms
Outer membrane—Extra
membrane similar to cell
membrane but also
containing popolysaccharide.
Controls flow of materials,
and portions of it are toxic
to mammals when released.
Actin cytoskeleton—Long fibers
of proteins that encircle the cell
just inside the cell membrane and
contribute to the shape of the cell.
Cytoplasm—Water-based
solution filling the entire cell.
Cell wall—A semirigid casing
that provides structural support
and shape for the cell.
• On average, prokaryotic cells are 1 µm (microns
-  can range from 0.05 -0.2 µm ( nanobes ) to
750 µm
Pilus—An elongated, hollow
appendage used in the transfer
of DNA to other cells.
Capsule (tan coating)—A coating or layer of
molecules external to the cell wall. It serves
protective, adhesive, and receptor functions.
It may fit tightly or be very loose and diffuse.
Also called slime layer and glycocalyx.
Inclusion/Granule—Stored nutrients such
as fat, phosphate, or glycogen deposited in
dense crystals or particles that can be
tapped into when needed.
• Cells of one species may vary in shape and size
-  this is pleomorphism caused by variations
in cell wall structure
Plasmid—Double-stranded DNA circle
containing extra genes.
Flagellum—Specialized appendage attached
to the cell by a basal body that holds a long,
rotating filament. The movement pushes the
cell forward and provides motility.
In Some Bacteria (not shown)
Endospore (not shown)—
Dormant body formed within
some bacteria that allows for their
survival in adverse conditions.
Intracellular membranes
(not shown)
© Science Photo Library RF/Getty Images
Arrangement of Cocci Resulting from
Different Planes of Cell Division
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Division in
one plane
Diplococcus Streptococcus
(two cells) (variable number
of coci in chains)
Division in two
perpendicular
planes
Tetrad (cocci in
packets off our)
Sarcina
Division in
(packet of several planes
8–64 cells)
Irregular clusters
(number of cells varies)
Staphylococci and
Micrococci`
(a)
(b)
(c)
External Structures
Concept Check
Which of the following structures are possessed by
some but not all prokaryotes?
Flagella – Prokaryotic
Propellers
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Bacterial locomotion
A. Ribosomes
B. A cell membrane
C. One or more chromosomes
D. Flagella
• Three distinct parts
Filament
• Comprised of many
proteins
Hook
Rod
Rings
(a)
• 360o
Flagellar Arrangements
• 
• 
rotation
Outer
membrane
Cellwall
Basal
body
Cell
membrane
(b)
Noreen R. Francis, Gina E. Sosinsky, Dennis Thomas and David J. DeRosier, Isolation, Characterization and Structure of Bacterial
Flagellar Motors Containing the Switch Complex, Journal of Molecular Biology, Vol 235, Issue 4, 27 January 1994, Pages 1261–1270.
Bacterial Movement
Monotrichous: single
flagellum
• Bacteria move in response to
chemical signals
(chemotaxis)
Lophotrichous: small
bunches or tufts of
flagella
• Receptors bind extracellular
molecules, which triggers
flagellum to rotate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Straight
Tumble
(a) General motility of a singular flagellum
Straight
(b) Peritrichous motility
• 
Amphitrichous: flagella at
both poles of the cell
• Runs: smooth linear
movement toward a stimulus
• 
Peritrichous: flagella
dispersed randomly over
the surface of the cell
• Tumbles: flagellar rotation
reverses, causing the cell to
stop and change its course
Tumble
Glycocalyx
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
•  Composed of polysaccharides, proteins or both
Prokaryotic Appendages
•  Varies in thickness
• Fimbriae: used for attachment
•  Used to avoid phagocytosis and for adhesion (biofilms)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Pili: used for attachment and
genetic exchange during
conjugation
Fimbriae
Glycocalyx
First colonists
Organic surface
coating
Surface
(a)
Pili
Cells stick to
coating.
Glycocalyx
slime
As cells divide, they
form a dense mat
bound together by
sticky extracellular
deposits.
Additional microbes
are attracted to
developing film and
create a mature
community with
complex function.
Catheter
surface
© L. Caro/SPL/Photo Researchers
Cell
cluster
(b)
b: © Science VU–Charles W. Stratton/Visuals Unlimited
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Capsule
Cell Envelope
•  Bound more tightly to the
cell, denser and thicker
than a slime layer
• Lies outside of the cytoplasm
• Composed of two or three basic layers:
-  cell wall
•  Visible by negative
staining
•  Produces a sticky
(mucoid) character to
colonies
-  cell membrane
Capsule
-  outer membrane in some bacteria
Cellbody
•  Encapsulated bacterial
(a)
cells generally have
greater pathogenicity
(b)
(a): © John D. Cunningham/Visuals Unlimited; b: Fig 1 from Brett J. Pellock, Max Teplitski, Ryan P. Boinay, W. Dietz Bauer, and Graham C. Walker, A
LuxR Homolog Controls Production of Symbiotically Active Extracellular Polysaccharide II by Sinorhizobium meliloti. Journal of Bacteriology,
September15, 2002, Vol. 184, No. 18, p. 5067–5076. Reproduced with permission from American Society for Microbiology.
Gram Positive Cell
Peptidoglycan Cell Wall
•  Repeating framework of long glycan (sugar) chains crosslinked by short peptide (protein) fragments
•  Present in most bacteria
• 
Thick peptidoglycan
• 
Teichoic acid, lipoteichoic acid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
•  Provides strength to resist rupturing due to osmotic pressure
• 
One membrane
Gram-Positive
Wall teichoic acid
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a) The peptidoglycan can be seen as a crisscross
network pattern similar to a chainlink fence.
CH2OH
O
Glycan chains
M
O
O
G
O
O
M
O
G
O
O
O
G
O
O
O
O
O
O
O
G
M
Peptidoglycan
Envelope
CH2OH
O
G
O
M
H3 C C H
G
O
Cell membrane
H3 C C H
C
O
M
G
M
M
G
O
M
M
M
G
O
M
G
M
M
G
O
M
C
M
Membrane proteins
G
M
Peptide cross-links
(b) It contains alternating glycans (G and M) bound together in
long strands. The G stands for N-acetyl glucosamine, and
the M stands for N-acetyl muramic acid.
Tetrapeptide
O
G
O
O
O
O
G
Lipoteichoic acid
L –alanine
L – alanine
D – glutamate
D –glutamate
L –lysine
D –alanine
– glycine
– glycine
– glycine
–
D – alanine
– glycine glycine
L – lysine
Interbridge
(c) A detailed view of the links between the muramic acids.
Tetrapeptide chains branching off the muramic acids connect
by interbridges also composed of amino acids. It is this linkage
that provides rigid yet flexible support to the cell and that may
be targeted by drugs like penicillin.
• Thin peptidoglycan
Gram Negative Cell
The Gram Stain: Developed by
Hans Christian Gram (1884)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Lipopolysaccharide
Gram-Negative
Lipoproteins
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Porin proteins
• Two membranes
Lipopolysaccharides
Outer membrane layer
Phospholipids
• Porins
Step
Microscopic Appearance of Cell
Peptidoglycan
Gram (+)
Gram (–)
Chemical Reaction in Cell Wall
(very magnified view)
Gram (+)
Gram (–)
1. Crystal violet
First, crystal violet is added to the cells in a smear. It stains them
all the same purple color.
Cell membrane
Both cell walls affix the dye
Membrane proteins
2. Gram s iodine
Then, the mordant, Gram s iodine, is added. This is a stabilizer that
causes the dye to form large complexes in the peptidoglycan meshwork
of the cell wall. The thicker gram-positive cell walls are able to more
firmly trap the large complexes than those of the gram-negative cells.
Periplasmic
space
Membrane
protein
3. Alcohol
Application of alcohol dissolves lipids in the outer membrane and
removes the dye from the peptidoglycan layer—only in the
gram-negative cells.
4. Safranin (red dye)
Because gram-negative bacteria are colorless after decolorization, their
presence is demonstrated by applying the counterstain safranin in the
final step.
© McGraw-Hill Companies, Inc.
Dye complex
trapped in wall
No effect
of iodine
Crystals remain
in cell wall
Outer membrane
weakened; wall
loses dye
Red dye masked
by violet
Red dye stains
the colorless cell
Acid-Fast Bacteria
• Mycobacterium sp. and Nocardia sp.
• Contain mycolic acid (a wax)
Cell-Wall Deficient Bacteria
•  Cell membrane stabilized by sterols, is resistant to lysis i.e.
Mycoplasma pneumoniae
•  Other cell-wall deficient types called L forms are linked to
infections
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Modified Gram-positive structure
• Must use the acid-fast stain to ID important
pathogens causing:
-  tuberculosis
Mutation or chemical treatment
GramPositive
Cell wall
(peptidoglycan)
Cell membrane
Cell membrane
Peptidoglycan
lost
Protoplast
(a)
Mutation or chemical treatment
-  leprosy
Outer membrane
GramNegative
(b)
Outer membrane
Peptidoglycan
Cell membrane
Cell membrane
Peptidoglycan
lost
Spheroplast
Cytoplasmic Membrane
Lipopolysaccharide
Case File
Artwork
• Located in the outermost layer of the outer
membrane (OM) in gram-negative bacteria
• Lipid A (endotoxin) stimulates fever and shock
Case File
Artwork
• A lipid bilayer with proteins embedded
-  bacterial cell membranes contain primarily
phospholipids (30%–40% of the membrane
mass) and proteins (60%–70% of the
membrane mass)
• Provides a site for reactions
-  contains enzymes of respiration and ATP
synthesis since prokaryotes lack
mitochondria
• A major action of the cell membrane is to
regulate the passage of nutrients into and out of
the cell
The Cytoplasm
Case File
Artwork
Bacterial DNA
• 70-80% water
Case File
Artwork
• Soluble proteins, salts, carbohydrates
• DNA is aggregated in a dense area of the cell
called the nucleoid
• Site of nearly all chemical reactions
• Many bacteria contain other, nonessential pieces
of DNA called plasmids
• Contains the DNA in the nucleoid
Prokaryotic Ribosome
Inclusions or Granules: Storage Bodies
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Two subunits
(30S and 50S)
• Total size is 70S (versus
80S in eukaryotes)
• DNA of most bacteria exists in the form of a
single circular bacterial chromosome
Case File
Artwork
Large
subunit
(50S)
Small
subunit
(30S)
• 
Non-membrane bound granules
• 
Usually for storage of nutrients
The Cytoskeleton
• 60% rRNA and 40%
protein
• 
Peptidoglycan layer determines shape of many
bacteria
• Translates mRNA into
proteins
• 
Others use protein fibers composed of actin
and tubulin to alter cell shape
Ribosome (70S)
Bacterial Endospores
A Typical Sporulation Cycle in Bacillus Species
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Dormant bodies
Spore coats
Chromosome
Case File
Artwork
•  Heat resistance due to calcium and dipicolinic acid
content
1
Vegetative cell begins to
be depleted of nutrients.
Cortex
Chromosome
Core of spore
Cell wall
•  Cortex, spore coats protect against radiation and
chemicals
•  Metabolically active vegetative cells can undergo
sporulation
•  Sporulation is not a reproductive function for most
bacteria
• When spores of Clostridium sp. are embedded in
a wound with dead tissue, they can germinate,
grow, and release toxins
9
8
2
Exosporium
Spore coat
Cortex
Core
Frees pore is
released with the
loss of the
sporangium.
7
Cell membrane
Germination:
spore swells
and releases
vegetative cell.
3
Forespore
Sporangium
4
Mature
endospore
Cortex
6
Chromosome is
duplicated and
separated.
Cell is septated
into a sporangium
and forespore.
Sporangium engulfs
forespore for further
development.
Early spore
5
Cortex and
outer coat layers
are deposited.
Sporangium begins to
actively synthesize
spore layers around
forespore.
© George Chapman/Visuals Unlimited
Archaea
• 
Prokaryotic microorganisms
• 
Many are found in extreme environments (i.e.
psychrophiles)
• 
Different from members of the domains Bacteria and Eukarya
in terms of: cell structure, metabolism, genetics
Classification Systems
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Table 3.2 Comparison of Three Cellular Domains
Characteristic
Bacteria
Archaea
Eukarya
Cell type
Prokaryotic
Prokaryotic
Eukaryotic
Chromosomes
Single, or few circular
Single, circular
Several, linear
Types of ribosomes
70S
80S
Contains unique ribosomal RNA
signature sequences
Number of sequences shared
with Eukarya
Protein synthesis similar to Eukarya
+
70S but structure is similar
to 80S
+
1
3
(all)
+
+
Presence of peptidoglycan in cell wall
+
Cell membrane lipids
Fatty acids with ester linkages Long-chain, branched
Fatty acids with ester
hydrocarbons with ether linkages linkages
Sterols in membrane
•  For differentiating and identifying unknown microbial species
i.e. Bergey s Manual of Determinative Bacteriology (phenotypic data)
+
•  For studying prokaryotic relationships and origins
i.e. Bergey s Manual of Systematic Bacteriology (rRNA sequencing data)
(some exceptions)
+
Prokaryotic Classification Systems
Case File
Artwork
• Bergey s Manual of Determinative Bacteriology
organizes the prokaryotes into four major divisions
based on cell wall structure:
-  Gracilicutes: gram-negative cell walls and
thus are thin-skinned
-  Firmicutes: gram-positive cell walls that
are thick and strong
-  Tenericutes: lack a cell wall and thus are
soft
-  Mendosicutes: archaea with unusual cell
walls
Species and Subspecies in Prokaryotes
Case File
Artwork
• Theoretically, a collection of bacterial cells, all of
which share an overall similar pattern of traits
and 70%–80% of their genes
• Members of given species can show variations
-  subspecies, strain, or type are terms used
to designate bacteria of the same species
that have differing characteristics
-  serotype refers to representatives of a
species that stimulate a distinct pattern of
antibody (serum) responses in their hosts