3
Bacteria and Archaea
CHAPTER OVERVIEW
This chapter provides a description of the prokaryotic cell, including bacterial and archaeal cells. The
discussion begins with the general features of size, shape, and arrangement of prokaryotic cells. Then the
general features of biological membranes and the specific features of prokaryotic membranes are given. The
cell wall is discussed with special reference to the differences between the cell walls of gram-positive bacteria
and gram-negative bacteria, differential staining reactions, and the nature of S-layers. Important internal
structures of prokaryotes, such as the cytoplasmic matrix, ribosomes, inclusion bodies, and the nucleoid are
described. Structures external to the cell, such as pili, fimbriae, and flagella lead into a discussion of cell
motility and chemotaxis. The chapter concludes with a description of the structure and functions of bacterial
endospores.
CHAPTER OBJECTIVES
After reading this chapter you should be able to:
•
•
•
•
•
•
•
•
•
identify major prokaryotic cell structures in a drawing or photomicrograph
describe the various sizes, shapes, and cellular arrangements exhibited by prokaryotes
describe the bacterial plasma membrane and the limited internal membrane structures found in
prokaryotes
compare the structure of gram-positive and gram-negative bacterial cell walls and explain how the
differences between the two contribute to their Gram reaction
describe the appearance, composition, and function of the various internal structures found in prokaryotic
organisms (such as inclusions, ribosomes, and the nucleoid)
describe external structures such as capsules, fimbriae, and flagella
diagram and describe the various arrangements of bacterial flagella
describe how bacteria use their locomotive ability to swim toward chemical attractants and away from
chemical repellents
describe the production of the bacterial endospore and how it enables endospore-forming bacteria to
survive harsh environmental conditions and renew growth when the environment becomes conducive to
growth
CHAPTER OUTLINE
I.
II.
Prokaryotes
A. Bacteria and Archaea are grouped together as prokaryotes because they lack a nucleus and
generally do not have membrane-bound organelles or an endomembrane system
B. Bacteria and Archaea are very distinct and the broad term, prokaryote, is misleading
Common Features of Bacterial and Archaeal Cell Structure
A. Shape, arrangement, and size
1. Most prokaryotes are spheres (cocci) or rods (bacilli)
a. During the reproductive process, some cocci remain attached to each other to form pairs
(diplococci), chains, clusters, square planar configurations (tetrads), or cubic
configurations (sarcinae)
b. Some rods are so short and wide that they appear to be ovals (coccobacilli); most rods
occur singly, but some form pairs or chains
19
2.
Other shapes include: curved rods (vibrios); rigid helices (spirilla), and flexible helices
(spirochetes); a few are flat; filaments, which can produce a network, are called a mycelium;
bacteria that exhibit more than one form are called pleomorphic
3. Prokaryotic cells vary in size (generally 1 to 5 µm) although they are typically smaller than
most eukaryotic cells; there have been reports of nanobacteria (0.2 µm to less than 0.05 µm in
diameter) and of very large prokaryotes (up to 750 µm in diameter)
4. Microbial sizes provide advantages such as greater surface-to-volume ratios (small cells) or
resistance to predation (large cells)
B. Prokaryotic cell structure
1. A variety of structures (cell wall, periplasmic space, plasma membrane, nucleoid, ribosomes,
inclusion bodies, flagella, capsules, and slime layers) are observed in prokaryotic cells
2. Not all structures are found in every genus; prokaryotic cells are morphologically simpler than
eukaryotic cells
C. Cell organization
1. Bacterial and archaeal cells often share a common organization
2. Bacterial and archaeal cells are surrounded by a cell envelope with complex cell walls; they
lack many internal features common in eukaryotic cells
III. Bacterial Cell Envelopes
A. The cell envelope includes the plasma membrane, cell wall, and other external layers of the cell
B. The plasma membrane serves several functions:
1. It retains the cytoplasm and separates the cell from its environment
2. It serves as a selectively permeable barrier
3. It contains transport systems used for nutrient uptake, waste excretion, and protein secretion
4. It is the location of a variety of crucial metabolic processes including respiration,
photosynthesis, lipid synthesis, and cell wall synthesis
5. It contains special receptor molecules that enable detection of and response to chemicals in the
surroundings
C. The fluid mosaic model of membrane structure
1. This model, proposed by Singer and Nicholson, states that membranes are lipid bilayers with
floating proteins
2. Cell membranes are very thin (5–10 nm thick); the lipids are amphipathic, having hydrophilic
(interact with water) head groups and long hydrophobic (insoluble in water) tails; the head
groups face out of the membrane while the tails are buried in the membrane to form bilayers
3. Two types of proteins are associated with the lipid bilayer of the membrane: peripheral
(loosely associated and easily removed) and integral (embedded within the membrane and not
easily removed)
D. Bacterial lipids
1. The plasma membrane of bacteria consists of a phospholipid bilayer with hydrophilic surfaces
and a hydrophobic interior; bacterial membranes lack sterols, but many contain sterol-like
molecules called hopanoids that help stabilize the membrane
2. Bacteria do not have membranous organelles, but can have internal membrane systems with
specialized functions such as photosynthesis or respiration
IV. Bacterial Cell Walls
A. The cell wall is a rigid structure that lies just outside the plasma membrane; it creates characteristic
shapes for the bacteria and protects from osmotic lysis and toxins, often while increasing
pathogenicity
B. Overview of bacterial cell wall structure
1. The cell walls of most bacteria contain peptidoglycan (murein)
2. The cell walls of gram-positive bacteria and gram-negative bacteria differ greatly, but both
have the periplasmic space between the cell wall material and the plasma membrane
C. Peptidoglycan structure
1. Peptidoglycan is a polysaccharide polymer composed of two sugar derivatives with peptide
linkers; the polysaccharide polymer is a linear chain of alternating N-acetylglucosamine
(NAG) and N-acetylmuramic acid(NAM) moieties
20
2.
Polysaccharide chains of peptidoglycan are cross-linked via a peptide interbridge attached to
the sugar backbone via a short peptide chain; these peptides contain some amino acids not
found in proteins; cross-linking adds strength to the peptidoglycan mesh
3. Variations in peptidoglycan structure are seen in certain bacterial groups and can be diagnostic
D. Gram-positive cell walls
1. They consist of a thick wall composed of many layers of peptidoglycan and large amounts of
teichoic acids
2. Techoic acids are polymers with a glycerol and phosphate backbone that span the cell wall and
likely enhance its structural stability
3. The periplasmic space of gram-positive cells is usually thin and contains only a few secreted
proteins (exoenzymes)
4. Most gram-positive bacteria also have a layer of proteins (S-layer proteins) on the outer
surface of the peptidoglycan that have a role in wall synthesis and virulence
5. Acid-fast bacteria include mycolic acids in their cell walls
E. Gram-negative cell walls
1. The gram-negative cell wall is more complex than the gram-positive cell wall; and has a thin
layer of peptidoglycan surrounded by an outer membrane
2. The periplasmic space is often wide and contains many different proteins; some are involved
with energy conservation or nutrient acquisition
3. The outer membrane is composed of lipids, lipoproteins, and lipopolysaccharides (LPS);
Braun's lipoprotein attaches the outer membrane to the peptidoglycan
4. LPS are large complex molecules composed of lipid A, core polysaccharides, and O antigen
carbohydrate side chains; LPS stabilize the outer membrane, protect against some toxins, and
can cause strong host immunological responses, acting as an endotoxin
5. The outer membrane is more permeable than the plasma membrane because of porin proteins
that form channels through which molecules smaller than 600 daltons can pass
F. Mechanism of Gram staining
1. After staining with crystal violet, constriction of the thick peptidoglycan layer of gram-positive
cells during decolorization prevents the loss of the crystal violet stain
2. The thinner, less cross-linked peptidoglycan layer of gram-negative bacteria does not retain the
stain, and thus more readily decolorized when treated with alcohol
G. Cell walls and osmotic protection
1. The cell wall prevents swelling and lysis of bacteria in hypotonic solutions; in hypertonic
habitats, the plasma membrane shrinks away from the cell wall in a process known as
plasmolysis
2. Bacteria without cell walls (by removal with lysozyme or through peptidoglycan synthesis
inhibition by penicillin) called spheroplasts are osmotically sensitive
3. Mycoplasmas lack a cell wall and tend to be pleomorphic
V. Layers Outside the Cell Wall
A. Capsules and slime layers
1. Capsules and slime layers (also known as glycocalyx) are layers of polysaccharides lying
outside the cell wall; they protect the bacteria from phagocytosis, desiccation, viral infection,
and hydrophobic toxic materials such as detergents; they also aid bacterial attachment to
surfaces and gliding motility
2. Capsules are well organized, whereas slime layers are diffuse and unorganized
B. S-layers
1. S-layers are regularly structured layers of protein or glycoprotein outside of the cell wall
2. S-layers protect against ion and pH fluctuations, osmotic stress, and hydrolytic enzymes; can
help maintain cell shape and envelope rigidity, promote cell adhesion, and protect against host
defenses
VI. Archaeal Cell Envelopes
A. Archaeal plasma membranes
1. Lipids have branched isoprene hydrocarbons attached to glycerol by ether links rather than
straight-chain fatty acids attached to glycerol by ester links, as seen in bacteria and eukaryotes
21
2.
Long diether and tetraether structures that form monolayer membranes are found in some
archaea
B. Archaeal Cell Walls
1. Archaea can stain either gram positive or gram negative, but their cell wall structure differs
significantly from that of bacteria
2. The most common archaeal cell wall is an S-layer of protein or glycoprotein; other protein
layers or condroitin-like materials can be found outside of the S-layer
3. Pseudomurein is often found between the plasma membrane and the S-layer; it is similar to
peptidoglycan but has different amino acids in its cross-links, uses N-acetyltalosaminuronic
acid, and has different glycosidic linkages
4. Some archaea have no S-layer, but have a thick layer of pseudomurein
VII. Cytoplasm of Bacteria and Archaea
A. The cytoplasmic matrix is the substance bounded by the plasma membrane; it is often packed with
ribosomes and inclusion bodies
B. The prokaryotic cytoskeleton has homologs of the elements seen in eukaryotes, filaments of actin,
tubulin, and intermediate filament proteins
C. Intracytoplasmic membranes are often involved in energy metabolism in nitrifying and
photosynthetic bacteria; unique ladderene lipids are found in anammoxosomes
D. Inclusions
1. Many inclusions are granules of organic or inorganic material that are stockpiled by the cell
for future use; some are not bounded by a membrane, but others are enclosed by a singlelayered membrane
2. Storage inclusions include glycogen (carbon storage), poly--hydroxybutyrate (carbon
storage), polyphosphate granules (energy and phosphorus storage), sulfur globules (wastes),
and cyanophycin granules (nitrogen storage in cyanobacteria)
3. Carboxysomes are microcompartments that accumulate carbon dioxide and the enzyme
ribulose-1,5-bisphosophate carboxylase
4. Gas vacuoles are composed of hollow protein sacs that are filled with gases and used for
buoyancy control in aquatic environments; magnetosomes are magnetite granules that provide
orientation in the Earth's magnetic field
E. Ribosomes
1. Ribosomes are the site of protein synthesis (translation)
2. They are complex structures consisting of protein and rRNA (ribosomal RNA)
3. Bacterial and archaeal ribosomes are 70S with 50S and 30S subunits; although differences are
apparent in ribosomal protein and rRNA components, ribosomes are similar across cells from
all three Domains
VIII. The Nucleoid
A. The nucleoid is an irregularly shaped region in which the chromosome of the prokaryote is found
1. In most prokaryotes, the nucleoid contains a single circular chromosome, though some have
more than one chromosome or have one or more linear chromosomes
2. The nucleoid is not membrane bound, although rare exceptions have been reported
B. The bacterial chromosome is an efficiently packed DNA molecule that is looped and supercoiled
extensively; there is evidence of histone-like proteins
IX. Plasmids
A. Plasmids are small, circular DNA molecules that are not part of the bacterial chromosome
1. Plasmids have their own replication origins, replicate autonomously, and are stably inherited
2. Episomes are plasmids that can exist either with or without being integrated into the host
chromosome
3. Plasmids can be eliminated from a cell by a process called curing, which can occur either
spontaneously or as a result of treatments that inhibit plasmid replication but do not affect host
cell reproduction
B. Conjugative plasmids (fertility factors, F factors, or F plasmids) are episomes that usually have
genes for sex pili and can transfer copies of themselves to other bacteria during conjugation
22
C.
Resistance factors (R plasmids) have genes for resistance to various antibiotics; some are
conjugative; however, they usually do not integrate into the host chromosome; R factors can be
transferred to other cells even across species lines, spreading antibiotic resistance, a major public
health concern
D. Col plasmids carry genes for the synthesis of bacteriocins (e.g., colicins), proteins that kill other
bacterial species
E. Other types of plasmids include virulence plasmids, which may carry a gene for toxin production,
and metabolic plasmids, which carry genes for enzymes that utilize certain substances as nutrients
(aromatic compounds, pesticides, etc.)
X. External Structures
A. Pili and fimbriae are short, thin, hairlike appendages that mediate bacterial attachment to surfaces
(fimbriae) or to other bacteria during sexual mating (sex pili); fimbriae tend to be narrower in
diameter and shorter than sex pili
B. Flagella
1. Flagella are threadlike locomotor appendages extending outward from the plasma membrane
and cell wall; they may be arranged in various patterns:
a. Monotrichous—a single flagellum
b. Amphitrichous—a single flagellum at each pole
c. Lophotrichous—a cluster (tuft) of flagella at one or both ends
d. Peritrichous—a relatively even distribution of flagella over the entire surface of the
bacterium
2. The flagellum consists of a hollow filament composed of a single protein known as flagellin;
the hook is a short, curved segment that links the filament to the basal body, a series of rings
that drives flagellar rotation
3. Flagellar synthesis involves many genes for the hook and basal body, as well as the gene for
flagellin; new molecules of flagellin are transported through the needlelike structure (like a
type III secretion system) so that the growth of the flagellum is from the tip, not from the base
4. Archaeal flagella tend to be thinner with more than one type of flagellin subunit, are not
hollow, and have unique hook and basal body analogs
XI. Motility and Chemotaxis
A. Motility
1. Motility in prokaryotes is not aimless; responses are made to temperature, light, oxygen,
osmotic pressure, and gravity; chemotaxis is directed movement of bacteria either toward a
chemical attractant or away from a chemical repellent
2. Prokaryotic flagella rotate to create motion (like a propeller); the direction of flagellar rotation
determines the nature of bacterial movement: counterclockwise rotation causes forward motion
(called a run) and clockwise rotation disrupts forward motion (resulting in a tumble)
3. The basal body is the motor that drives the flagellum; it is powered by a proton motive force
4. Although archaeal flagella rotate in both directions, run and tumble movement is not observed
5. Prokaryotes can move by other mechanisms: in spirochetes, axial fibrils cause movement by
flexing and spinning; other prokaryotes exhibit twitching or gliding motility, a mechanism
involving pili by which they move along solid surfaces
B. Chemotaxis
1. The concentrations of attractants and repellents are detected by chemoreceptors in the
periplasmic space or the plasma membrane
2. Directional travel toward a chemoattractant (biased random walk toward attractant) is caused
by lowering the frequency of tumbles (twiddles), thereby lengthening the runs when traveling
up the gradient, but allowing tumbling to occur at normal frequency when traveling down the
gradient
3. Directional travel away from a chemorepellent (biased random walk away from repellent)
involves similar but opposite responses
XII. Bacterial Endospores
A. The bacterial endospore is a special, resistant, dormant structure formed by some bacteria; it enables
them to resist harsh environmental conditions
23
B.
C.
D.
Endospore structure is complex, consisting of an outer covering called the exosporium, a spore coat
beneath the exosporium, the cortex beneath the spore coat, and the spore cell wall, which is inside
the cortex and surrounds the core
Endospore formation (sporulation) normally commences when growth ceases because of lack of
nutrients; it is a complex, multistage process
Transformation of dormant endospores into active vegetative cells is also a complex, multistage
process that includes activation (preparation) of the endospore, germination (breaking of the
endospore’s dormant state), and outgrowth (emergence of the new vegetative cell)
TERMS AND DEFINITIONS
Place the letter of each term in the space next to the definition or description that best matches it.
____ 1.
____ 2.
____ 3.
____ 4.
____ 5.
____ 6.
____ 7.
____ 8.
____ 9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
____ 15.
____ 16.
____ 17.
____ 18.
____ 19.
____ 20.
____ 21.
Bacteria that are roughly spherical in shape
Bacteria that are rod shaped
Short, thin, hairlike structures that mediate bacterial
attachment to other bacteria during mating
Curved, rod-shaped bacteria
The vegetative cell (mother cell) in which an
endospore forms
Branched network of hyphae
Long, rod-shaped bacteria that are twisted into rigid
helices
Long, rod-shaped bacteria that are twisted into flexible
helices
The domain of prokaryotic organisms distinguished by
their rRNA, cell wall composition, lipids, and other
features
Bacteria that lack a single characteristic shape and that
therefore vary in shape
The structural component of bacterial cell walls that is
also called peptidoglycan
Molecules or regions of molecules that readily interact
with water
Molecules or regions of molecules that are insoluble in
water, or do not readily react with water
Proteins that are loosely associated with a membrane
and that can therefore be easily removed
Proteins that are not easily extracted from membranes
and that are insoluble in aqueous solutions when freed
of lipids
Plasma membrane and everything contained within
A unit of measure of the sedimentation velocity in a
centrifuge
The nonmembrane-bound region of a prokaryotic cell
in which the DNA is located
A circular, double-stranded DNA molecule in
prokaryotes that can exist and replicate independently
of the chromosome
A gap between the plasma membrane and the cell wall
of bacteria
Organisms with a peptidoglycan-like polymer with
L-amino acids instead of D-amino acids
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____ 22. Enzymes that are
secreted out of the cell to
aid in the acquisition and
digestion of nutrients
from the environment
____ 23. Movement of water
across selectively
permeable membranes
from dilute solutions
(higher water
concentration) to more
concentrated solutions
(lower water
concentration)
____ 24. Bursting of cells that
occurs when cells are
placed in hypotonic
solutions so that water
flows in the cell
____ 25. Shrinkage of the plasma
membrane away from
the cell wall that occurs
when cells are placed in
hypertonic solutions so
that water flows out of
the cell
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
o.
p.
q.
r.
s.
t.
u.
v.
w.
x.
y.
z.
aa.
bb.
cc.
dd.
ee.
ff.
gg.
hh.
ii.
jj.
kk.
ll.
mm.
nn.
oo.
pp.
qq.
rr.
Archaea
axial filament
bacilli
capsule
carboxysomes
chemotaxis
cocci
conjugative plasmid
cyanophycin granules
endospore
episome
exoenzymes
fimbriae
germination
glycocalyx
glycogen
hydrophilic
hydrophobic
inclusion bodies
integral proteins
lysis
metabolic plasmid
murein
mycelium
nucleoid
osmosis
peripheral proteins
periplasmic space
plasmid
plasmids
plasmolysis
pleomorphic
protoplast
R factor
sex pili
S-layer
slime layer
spirilla
spirochetes
sporangium
sporogenesis (sporulation)
Svedberg unit
Vibrios
virulence plasmid
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____ 26. Well-organized polysaccharides outside
the cell wall that are not easily washed
off
____ 27. Diffuse, unorganized polysaccharides
outside the cell wall that are easily
removed
____ 28. Protein or glycoprotein layer that
exhibits a pattern not unlike floor tiles
____ 29. Hairlike appendages that are thinner
than flagella and are usually involved in
attachment rather than motility
____ 30. A flexible filament that is used for
motility by spirochetes
____ 31. Movement toward chemical attractants
or away from repellents
____ 32. A structure formed by some species of
bacteria that is resistant to some
environmental stresses
____ 33. The process of forming endospores
within a vegetative cell
____ 34. The breaking of an endospore’s
dormant state as it begins to form a
vegetative cell
____ 35. Granules of organic or inorganic
material that are stockpiled by the cell
for future use
____ 36. A network of polysaccharides extending
from the surface of bacteria and other
cells
____ 37. Inclusion bodies that serve as a reserve
of the enzyme ribulose-1,5bisphosphate carboxylase; they may
also be the site of CO2 fixation
____ 38. Inclusion bodies that store extra
nitrogen for bacteria
____ 39. A polymer of glucose units; it serves as
a carbon storage reservoir for many
bacteria
____40. Small, circular DNA molecules that can
exist independently of the host
chromosome, that have their own
replication origins, that are
autonomously replicated, and that are
stably inherited
____41. A plasmid that can exist independent of
the host chromosome or be integrated
into it
____42. A plasmid that has genes for pili and
can transfer copies of itself to other
bacteria
____43. A plasmid that carries genes that encode
resistance to antibiotics
____44.
____45.
26
A plasmid that carries genes for a toxin,
and thus renders the host bacterium
pathogenic
A plasmid that carries genes for
enzymes that degrade environmental
substances such as aromatic compounds
and pesticides
IDENTIFICATION OF PROKARYOTIC STRUCTURES
Label the appropriate structures indicated on the accompanying figure. The terms to be used are listed below.
In the space beside each term provide a brief description of its structure and/or function.
1.
Capsule:
2.
Cell wall:
3.
Flagellum:
4.
Inclusion:
5.
Nucleoid:
6.
Periplasmic space:
7.
Plasma membrane:
8.
Ribosome:
9.
S-layer:
27
FLAGELLAR ARRANGEMENTS
Label each flagellar arrangement with the appropriate name.
1.
_______________________________
2.
_______________________________
3.
_______________________________
4.
_______________________________
BACTERIAL SHAPES
Label each bacterial shape.
1.
_______________________________
2.
_______________________________
3.
_______________________________
4.
_______________________________
5.
_______________________________
6.
_______________________________
rigid
flexible
28
BACTERIAL ARRANGEMENTS
Label each arrangement of spherical bacteria with the appropriate term.
1.
_______________________________
2.
_______________________________
3.
_______________________________
4.
_______________________________
planar configuration of four cells
5.
_______________________________
cubic configuration of eight cells
29
FILL IN THE BLANK
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
The
encompasses the cytoplasm of both prokaryotic and eukaryotic cells. It
is the chief point of contact with the cell’s ____________ and thus is responsible for much of its
relationship with the outside world.
The amphipathic property of lipids enables them to form a ____________ in membranes. Thus the outer
surface of the membrane is ____________, and the ____________ ends of the lipids are buried in the
interior of the membrane, away from the surrounding water.
The most widely accepted structural model for membranes is called the
model. In this model, proteins are associated with or embedded in a fluid lipid bilayer. Those proteins
embedded in the membrane are called
proteins; those proteins loosely attached to the
surface of the membrane are called
proteins.
An important constituent of the cell walls of gram-negative bacteria is lipopolysaccharide (LPS). This
complex molecule is composed of
___,
___
, and
side chain
(antigen).
In ____________ environments, a cell will lose water so that the plasma membrane shrinks away from
the cell wall. This is referred to as ____________.
The space between the cell wall and the plasma membrane is called the
. In
gram-negative bacteria, this space contains many proteins that participate in nutrient acquisition. In grampositive bacteria, this same function is performed by ____________ that are secreted out of the cell.
Solutes are less concentrated in ____________ environments than in cells. When cells are placed in this
type of environment, water will flow ____________, causing the cell to swell and eventually burst if the
plasma membrane is unprotected because the cell lacks a
.
Many bacteria are motile by means of
, which are composed of three parts. The largest
and most obvious part is the
, which extends from the cell surface. The
is embedded in the cell. The
is a short, curved segment that acts as a flexible coupling,
joining the basal body to the filament.
The direction of flagellar rotation determines the nature of bacterial movement. For bacteria with
peritrichous flagella, rotation in the ____________ direction propels the bacterium forward, while
rotation in the ____________ direction disrupts the bundle of flagella and causes the bacterium to
____________.
A bacterium travels in a straight line (a _____________) for a few seconds; then it stops and
____________; this is followed by a ____________ in a different direction. When exposed to a chemical
attractant gradient, a bacterium tumbles ____________ frequently when traveling up the gradient, but
tumbles at ____________ frequency if moving down the gradient.
A thin delicate covering called the
surrounds an endospore and the
lies directly below it. The latter is composed of several protein layers and may be fairly thick. As much as
half of the volume of the endospore may be occupied by the
, which is made of
peptidoglycan, and within this is the
(also called the core
wall), which surrounds the protoplast or
of the endospore.
Many aquatic bacteria contain
, which give the cells buoyancy and are composed of
many small, hollow, cylindrical structures called
.
The enzyme
hydrolyzes the bond connecting the sugars in peptidoglycan and therefore can
cause bacterial cells to lyse.
A
is a cell with its cell wall completely removed. A
is a cell having a
weakened or partially removed cell wall. The latter can be formed when gram-negative bacteria are
treated with penicillin. The penicillin inhibits
synthesis, but the outer membrane remains
intact.
If a bacterium is deflagellated, it will regenerate a flagellar filament. It is believed that
subunits, the protein subunits that make up the filament, are transported through the filament’s hollow
core. When they reach the tip, the subunits spontaneously aggregate. This is an example of
.
Chains of the polysaccharide
, which is observed in most bacterial cell walls, are
joined by cross-links between the peptides of each chain. In many cases the carboxyl group of the
30
terminal D-alanine in one peptide is connected directly to the amino group of diaminopimelic acid in the
other chain. However, in some bacteria a
connects the two peptides.
MULTIPLE CHOICE
For each of the questions below select the one best answer.
1.
2.
3.
Which of the following is NOT a function of
the plasma membrane?
a. It retains the cytoplasm.
b. It acts as a selectively permeable
barrier, allowing some molecules to
pass while preventing the movement of
others.
c. It maintains the various shapes of the
bacteria.
d. It is the location of a variety of
metabolic processes, including
respiration and photosynthesis.
Which of the following is NOT true of
prokaryotic plasmids?
a. They can exist and replicate
independently of the chromosome.
b. They are required for host growth
and/or reproduction.
c. They may carry genes for drug
resistance.
d. They may carry genes that give the
bacterium new useful metabolic
activities.
Lipopolysaccharide (LPS), which is found in
the outer membrane of gram-negative
bacteria, is also known as
a. teichoic acid.
b. exotoxin.
c. endotoxin.
d. murein.
4.
5.
6.
7.
31
Why is it thought that gram-positive cells
retain the primary stain of the Gram stain
while gram-negative cells do not?
a. Because the stain is bound to the thicker
peptidoglycan layer.
b. Because the alcohol removes the lipids
of the outer membrane, and thus the
trapped stain, from gram-negative
bacteria.
c. Because the alcohol shrinks the pores of
the thick peptidoglycan layer of grampositive cells.
d. Both (b) and (c) are correct.
Penicillin inhibits cell wall synthesis, but
cells will continue to grow normally in the
presence of penicillin if they are maintained
in a(n) ____________ environment.
a. hypotonic
b. isotonic
c. hypertonic
d. nonpolar
Which of the following refers to a network of
polysaccharides that extends from the surface
of a bacterium and aids in attachment of the
bacterium to surfaces?
a. lipoteichoic acid
b. lipopolysaccharide
c. outer membrane
d. glycocalyx
Which of the following is true of capsules?
a. They help bacteria resist phagocytosis
by host phagocytic cells.
b. They protect bacteria from desiccation.
c. They prevent the entry of bacterial
viruses.
d. All of the above are true of capsules.
8.
What will motile bacteria do when they are in
the presence of both attractants and
repellents?
a. move toward the attractant
b. compare both signals and respond to the
chemical with the most effective
concentration
c. move away from the repellent
d. move in a random fashion
9. Why are endospores of great practical
importance in industrial and medical
microbiology?
a. Because they are resistant to harsh
environments and thus increase the
survival of spore-forming bacteria as
compared to that of bacteria that do not
form spores.
b. Because many endospore-formers are
dangerous pathogens.
c. Both (a) and (b) are correct.
d. Neither (a) nor (b) is correct.
10. Where are extensive invaginations of the
plasma membrane usually observed?
a. in cyanobacteria and other
photosynthetic bacteria
b. in bacteria with high respiratory activity
c. Both (a) and (b) are correct.
d. Neither (a) nor (b) is correct.
11. Which of the following are examples of
inclusion bodies or materials found in
inclusion bodies?
a. volutin granules
b. poly-β-hydroxybutyrate (PHB)
c. polyphosphate
12.
13.
14.
15.
d. magnetosomes
e. All of the above.
Which of the following is the primary lipid
component of the membranes of extreme
thermophiles?
a. C20 diethers
b. C40 tetraethers
c. sulfolipids
d. cholesterol
Which of the following strengthens the cell
membranes of cell wall-less archaea?
a. diglycerol tetraethers
b. lipopolysaccharides
c. glycoproteins
d. All of the above are correct.
Populations can be cured of their plasmids by
treatments that inhibit plasmid replication but
that do not affect host DNA replication.
Which of the following has been used as a
curing agent?
a. UV and ionizing radiation
b. acridine mutagens
c. thymine starvation
d. All of the above have been used as
curing agents.
Which of the following is NOT encoded
within a virulence plasmid?
a. proteins that destroy other bacteria
b. genes that render the bacterium less
susceptible to host defense mechanisms
c. genes for the production of toxigenic
substances
d. All of the above may be encoded within
virulence plasmids.
TRUE/FALSE
____ 1.
____ 2.
____ 3.
____ 4.
____ 5.
____ 6.
____ 7.
____ 8.
The cell membrane is a rigid and relatively static structure.
Gas vacuoles are membranous structures that regulate buoyancy in cyanobacteria and other
photosynthetic bacteria. However, even though they are membranous, their vesicle walls contain no
lipids.
Sedimentation coefficients (measured in Svedberg units) are directly proportional to the molecular
weight of a particle and are unaffected by volume or shape.
Gram-positive cell walls have a thick layer of peptidoglycan but a rather simple overall structure,
while gram-negative cell walls have a thinner peptidoglycan layer but a more complex overall
structure.
Lipoteichoic acids are teichoic acids that are connected to lipids in the plasma membrane.
Porin proteins are found in the outer membrane of gram-negative bacteria and function in the
transport of molecules into the cell.
Mycoplasmas must be maintained in an isotonic environment because they lack a cell wall.
In the construction of flagella, the protein flagellin is added at the base of the flagellum so that first
the tip is constructed and then pushed outward by the addition of new material at the base.
32
____ 9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
____ 15.
____ 16.
____ 17.
____ 18.
____ 19.
Bacterial flagellar rotation appears to be powered by proton gradients or sodium gradients, but not
by ATP hydrolysis.
Prokaryotic organisms are so remarkably uniform that nearly all genera contain all of the structures
described in this chapter.
Pleomorphic bacteria are uniformly club-shaped.
Chemotactic receptors are directly coupled to the basal body of the flagella.
Archaeal membranes often have a monolayer rather than a bilayer structure.
The cytoplasmic matrix of prokaryotic cells contains a cytoskeleton.
Gliding motility is a means by which bacteria coast along solid surfaces.
Endospores have a high content of dipicolinic acid.
The glycocalyx is also called the cell envelope.
A plasmid that can exist independent of the host chromosome but that cannot be integrated into the
host chromosome is called an episome.
For a bacterium to be resistant to five different antibiotics, it must carry five different R factor
plasmids simultaneously.
CRITICAL THINKING
1.
Discuss why the plasma membrane is considered the external boundary of the cell, even though other
structures outside of the plasma membrane are considered part of the cellular anatomy.
2.
Discuss the nature of flagellar-mediated movement of bacteria. In particular, discuss how the direction of
rotation affects the direction of movement, and speculate how this movement is altered in the presence of
chemical attractants and repellents for which the bacterium has the appropriate chemoreceptors. Give
plausible mechanisms of the response to chemical attractants and/or repellents.
33
ANSWER KEY
Terms and Definitions
1. g, 2. c, 3. ii, 4. qq, 5. nn, 6. x, 7. ll, 8. mm, 9. a, 10. ff, 11. w, 12. q, 13. r, 14. aa, 15. t, 16. gg, 17. pp, 18. y,
19. cc, 20. bb, 21. a, 22. l, 23. z, 24. u, 25. ee, 26. d, 27. kk, 28. jj, 29. m, 30. b, 31. f, 32. j, 33. oo, 34. n, 35. s,
36. o, 37. e. 38. i. 39. p, 40. dd, 41. k, 42. h, 43. hh, 44. rr, 45. v
Flagellar Arrangements
1. monotrichous, 2. amphitrichous, 3. lophotrichous, 4. peritrichous
Bacterial Shapes
1. coccus, 2. coccobacillus, 3. bacillus, 4. vibrio, 5. spirilla, 6. spirochete
Bacterial Arrangements
1. diplococcus, 2. streptococcus, 3. staphylococcus, 4. tetrad, 5. sarcinae
Fill in the Blank
1. plasma membrane; environment 2. bilayer; hydrophilic; hydrophobic 3. fluid mosaic; integral; peripheral
4. lipid A; core polysaccharide; O 5. hypertonic; plasmolysis 6. periplasmic space; exoenzymes
7. hypotonic; inward; cell wall 8. flagella; filament; basal body; hook 9. counterclockwise; clockwise; tumble
(twiddle) 10. run; tumbles (twiddles); run; less; normal 11. exosporium; spore coat; cortex; spore cell wall;
core 12. gas vacuoles; gas vesicles 13. lysozyme 14. protoplast; spheroplast; peptidoglycan
15. flagellin; self-assembly 16. peptidoglycan; peptide interbridge
Multiple Choice
1. c, 2. b, 3. c, 4. d, 5. b, 6. d, 7. d, 8. b, 9. c, 10. c, 11. e, 12. b, 13. d, 14. d, 15. a
True/False
1. F, 2. T, 3. F, 4. T, 5. T, 6. T, 7. F, 8. F, 9. T, 10. F, 11. F, 12. F, 13. T, 14. F, 15. T, 16. T, 17. F, 18. F, 19. F
34