Important words and
concepts from Chapter 4, Black, 2002 (3/28/2003):
by Stephen T. Abedon (abedon.1@osu.edu)
for Micro 509
at the Ohio State University
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Course-external links are
in brackets Click [index] to access site index Click here to access
text’s website Vocabulary
words
are found below |
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(1) Chapter Title: Characteristics of Prokaryotic and Eukaryotic Cells
(a)
Found
at this site are additional pages of possibly related interest including: [a
tour of the cell (MicroDude)] [membrane structure and
function (MicroDude)] [supplemental cell biology lectures (MicroDude)]
PROKARYOTES (them) vs.
EUKARYOTES (us)
(a)
Across
all types of organisms, cells may be classified into two fundamental
morphological types: Prokaryotes and Eukaryotes
(b)
A
given organism will possess cells of one of these types, but not both (though
there is an exception to this rule, endosymbiosis, that
we will discuss)
(c)
[cell theory (Google Search)] [index]
(a)
Organisms
classified as prokaryotes have a number of defining features that differentiate
their cell type from the eukaryote cell type
(i)
Prokaryotic
cells lack a nucleus
(ii)
Prokaryotic
cells tend to lack other membrane-bound organelles (the nucleus, itself, also
represents a membrane-bound organelle)
(iii)
[more-complete comparison of
prokaryotic and eukaryotic cell features (Doc Kaiser’s Microbiology Web Page)] [index]
(b)
We
will focus in this lecture on the cellular anatomy of prokaryotic cells since
the majority of this course will deal with bacteria, which are prokaryotes
(c)
We
will additionally call attention to the existence of prokaryote-like organelles that are found in most eukaryotic
cells
(d)
Finally,
we will consider how membranes function
(e)
Prokaryotes
typically, though not exclusively, exist as unicellular organisms
(f)
[prokaryotic cells (Google Search)] [a prokaryotic cell]
[composition and functions of
bacterial structures] [index]
(a)
Organisms
that possess the eukaryotic cell type include
(i)
Animals
(ii)
Plants
(iii)
Fungi
(iv)
Algae
(v)
Protozoa
(b)
See Table 4.1, Similarities
and differences between prokaryotic and eukaryotic cells
(c)
[eukaryotic cells (Google Search)] [a eukaryotic cell]
[index]
(a)
An
even more fundamental means of distinguishing organisms than into prokaryotes
and eukaryotes is their categorization into domains (supplanting “kingdoms” the
domain is now the highest of taxonomic categories)
(b)
There
exist three domains
(i)
Archaea
(archaeobacteria) which are prokaryotes
(ii)
Bacteria
(eubacteria) which are prokaryotes
(iii)
Eukarya
which are eukaryotes
(c)
Note
that Table 4.1 compares and contrasts Bacteria with Eukarya, leaving Archaea
out; this is a typical emphasis within microbiology, and among microbiologists,
and we won’t fight it
(d)
[three-domain system
(Google Search)]
[universal tree (MicroDude)] [index]
(a)
Prokaryotic cells are
typically much smaller than eukaryotic cells
(b)
This
gives prokaryotic cells a large surface-to-volume ratio which makes up for
their comparative morphological simplicity
(c)
Eukaryotic
cells are larger and possess numerous internal membranes that help to make up
for their small plasma-membrane-to-cytoplasmic-volume ratio
(d)
Mitochondria
and chloroplasts, found as organelles in eukaryotic cells, on the other hand,
approximate the size of prokaryotic cells
(e)
A
large surface-to-volume ratio is advantageous for an organism that acquires
nutrients by absorption since there is comparatively more absorption surface
(the plasma membrane) and comparatively less of a requirement for absorbed
nutrients (the cytoplasmic volume)
(f)
Thus,
the small size as well as simple morphology of bacteria is well suited to their
absorption-of-nutrients-from-the-environment ecological niche
(g)
[size of prokaryotes
(Google Search)]
[index]
BACTERIA MORPHOLOGY
(7) Bacterial shapes (coccus, bacillus, coccobacillus, spirillum, spirochete)
(a)
Consistent
with the simple morphology and small size of bacteria, their basic shapes also
tend to be relatively simple
(b)
Bacterial
shapes may be typically divided into the following categories
(i)
Coccus (cocci) = spherical [arrangements of cocci]
(ii)
Bacillus (bacilli) = rod-shaped [arrangements of bacilli]
(iii)
Coccobacillus = intermediate to coccus
and bacillus
(iv)
Spirillum = wavy spiral-shaped [shape of spirillium]
(v)
Spirochete = corkscrew spiral-shaped
(vi)
Etc.
= square-shaped, star-shaped, filamentous, etc.
(c)
Bacterial
shapes, depending on the organism, can change subtly when cells are growing or
existing under different conditions, e.g., a shortening of rods as nutrient
concentrations are used up and therefore as growth rates decline; this will be
especially obvious as you attempt to classify the shape of such things as
stationary-phase Escherichia coli
(d)
See Figure 4.1, The most
common bacterial shapes
(e)
[bacterial shapes (Google Search)] [index]
(a)
Some
bacteria do not display a constant shape even during growth in an otherwise
unchanging, homogeneous environment
(b)
Such
bacteria are termed pleomorphic to indicate that they do not possess a
relatively constant standard shape even under relatively constant, standard
conditions
(9) Bacterial cell arrangements (diplo-, strepto-, tetrad, sarcina,
staphylo-)
(a)
While
some bacteria cells separate completely following division, others remain
attached
(b)
Attached
cells typically take on a characteristic arrangement that differs depending on
the bacteria, the bacterial shape, and the planes in which cell division occurs
[arrangements of cocci]
[arrangements of bacilli]
(c)
Typical
bacterial arrangements include:
(i)
Diplo-
= cells remain attached in pairs (e.g., diplococcus) [image, diplococcus]
(ii)
Strepto-
= cells remain attached in chains (e.g., streptococcus) [image, streptococcus]
[image, streptobacillus]
(iii)
Tetrads
= cells arranged in squares (note two planes of division) [image, tetrad arrangement]
(iv)
Sarcinae
= cells arranged in cubes (note three planes of division) [image, sarcina arrangement]
(v)
Staphylo-
= random planes of division resulting in sheets and clumps [image, staphylococcus]
[image, Staphylococcus aureus]
(d)
Bacilli
typically divide within only a single plane of division so are limited to
diplo- or strepto-forms [arrangements of bacilli]
(e)
See Figure 4.2, Arrangements
of bacteria
(f)
(g)
["cellular
arrangements" and bacteria (Google Search)] [sizes, shapes, and
arrangements of bacteria (Biol 230 Microbiology – Gary E. Kaiser)] [index]
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Sample
question: Full credit for 13 entered correctly
(with credit off for incorrect entries):
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BACTERIA ANATOMY
(10) Bacterial cellular anatomy
(a)
For
the sake of organization, bacterial cellular anatomy may be categorized into
(i)
Those
things found associated with the cell envelope
·
E.g.,
the plasma membrane, the cell wall, etc.
(ii)
Those
things found internal to the cell envelope
·
E.g.,
cytoplasm,
ribosomes,
nuclear regions, etc.
(iii)
Those
things found external to the cell envelope
·
E.g.,
capsules,
flagella,
pili,
glycocalyx,
etc.
(b)
See Figure 4.3, A typical
prokaryotic cell
(a)
The
cell wall of a bacteria
(i)
Is
semirigid
(ii)
Is
found externally to the plasma membrane
(iii)
Is
responsible for maintaining the cell shape
(iv)
Is
responsible for protecting bacteria against osmotic lysis
(v)
Consists
of peptidoglycan, a.k.a., murein
(vi)
Consists,
in Gram-positive bacteria, additionally of teichoic acid
(b)
Though
most bacteria possess cell walls, not all do
(c)
[bacterial cell wall
(Google Search)]
[cell wall anatomy]
[index]
(a)
The
Gram-negative bacteria cell wall differs from the cell wall of Gram-positive
bacteria in terms of
(i)
The
structure of the cell wall itself
(ii)
The
covering of the cell wall by an outer membrane
(iii)
The
existence of a distinct periplasm located between the outer membrane
and the inner membrane
(b)
[gram-negative cell wall
(Google Search)]
[structure of a Gram-negative
cell wall] [index]
(a)
The
outer membrane is a feature of Gram-negative bacteria but not Gram-positive
bacteria
(b)
The
outer membrane is found externally to the cell wall
(c)
The
outer membrane helps protect the cell wall and plasma membrane
from environmental poisons
(d)
The
outer membrane additionally contains (i.e., surrounds) the periplasmic space
(e)
See Figure 4.6b, The
bacterial cell wall
(a)
Inner
membrane is another name for the Gram-negative plasma membrane
(b)
[bacterial inner membrane
(Google Search)]
[enzymes of the inner membrane]
[index]
(15) Lipopolysaccharide (LPS, endotoxin)
(a)
A
component of the outer-leaflet of the outer membrane of
Gram-negative bacteria is LPS
(b)
LPS
consists of polysaccharide and Lipid A (the latter anchors the LPS into the
outer membrane)
(c)
Another
name for Lipid A is endotoxin
(d)
(“The
major cause of death for patients with cystic fibrosis is the massive chronic
infections with Pseudomonas aeruginosa that they
acquire… Bacteria adapt to the particular environment of the patients’ lungs by
synthesizing lipopolysaccharides
with a specific structure. This modification in lipid A is associated with an increased inflammatory response and
resistance to antimicrobial agents.” 1999, Science
286:1441-1443)
(e)
[lipopolysaccharide and
"outer membrane", LPS and "outer
membrane", endotoxin and "outer
membrane" (Google Search)] [index]
(16) Periplasmic space (periplasm)
(a)
The
periplasm is the volume between the inner and outer
membranes
(b)
Gram-negative
bacteria digest nutrients in the periplasm prior to the transport of the
nutrients into the cytoplasm
(c)
(Gram-positive
bacteria, by contrast, function more like fungi, employing exoenzymes that act beyond the cell to digest nutrients into
forms that may then be taken up by the cell)
(d)
In
addition to breaking down nutrients, the periplasm additionally serves as a
region in which potentially harmful substances are broken down (i.e.,
destroyed)
(e)
See Figure 4.6b, The
bacterial cell wall
(f)
[periplasmic space, periplasmic space (Google Search)] [index]
(a)
Note
that you are likely already somewhat familiar with Gram-negative-bacterial
structures (e.g., inner membrane, outer membrane, periplasmic space) since these structures are equivalently
found in mitochondria and chloroplasts
(b)
This
is because mitochondria and chloroplasts are, in fact, Gram-negative bacteria
(c)
Their
similarity to Gram-negative bacteria continues further, including the existence
in these eukaryote organelles of a nucleoid (nuclear regions)
and Gram-negative-bacteria-like ribosomes
(d)
See Figure 4.21,
Mitochondria
(e)
[periplasm and bacteria
(Google Search)]
[index]
(a)
The
Gram-positive cell wall differs from the Gram-negative cell wall in at
least three ways
(i)
It
is considerably thicker than the Gram-negative cell wall
(ii)
It
contains teichoic acid
(iii)
It
is directly exposed to the extracellular environment (or, at least, is not
covered by an outer membrane)
(b)
The
thickness of the cell wall allows the retention of the Gram stain thus accounting
for the Gram-positive staining of these bacteria
(i)
See Figure 4.6a, The
bacterial cell wall
(c)
[gram-positive cell wall
(Google Search)]
[index]
(a)
A
Gram-positive cell that is treated with lysozyme (a peptidoglycan-digesting
enzyme) within an isotonic environment (as we’ll define later) becomes
spherical and is called a protoplast
(b)
[note
that there seems to be an amazing lack of information on bacteria protoplasts
on the web; please let me know of any sites you know of on this
subject]
(c)
[protoplast and bacteria
(Google Search)]
[note that plant cells
that have had their cell walls removed
are also called protoplasts] [index]
(a)
Unlike
Gram-positive bacteria, the digestion of a Gram-negative bacterium with
lysozyme does not result in a complete removal of the outer membrane and these
cells are termed spheroplasts rather than protoplasts
(b)
[spheroplast and bacteria
(Google Search)]
[yeasts may also be spheroplasted] [Mycobacterium
paratuberculosis may be found in either a bacillary or spheroplast form] [antibiotic-treated Borrelia burgdorferi can take on a pleomorphic, not replicating
spheroplast-L-form variant] [index]
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Sample
question: Full credit for 13 entered correctly
(with credit off for incorrect entries):
|
MOVEMENT ACROSS MEMBRANES
(a)
The
plasma membrane of prokaryotes and eukaryotes are functionally equivalent,
though the prokaryote plasma membrane additionally serves in roles that
eukaryotes reserve for internal membranes (e.g., cellular respiration)
(b)
Membranes
consist of phospholipids which form into lipid bilayers because they have
both a hydrophilic and a hydrophobic end
(c)
These
lipid bilayers are impermeable to charged or large substances (e.g., ions or
sugars); they are thus said to be selectively permeable
(d)
See Figure 4.7, The fluid
mosaic model of the cell membrane
(e)
[plasma
membrane (Google
Search)] [figure,
cytoplasmic membrane (that fails to show asymmetry)] [index]
(22) Movement across membranes
(a)
Small,
hydrophobic substances typically can readily
pass through plasma membranes by simple diffusion
(b)
Passage
of charged or large substances through lipid bilayers is mediated by integral
membrane proteins
(c)
Other
proteins found in or on membranes serve as enzymes
(d)
[movement across membranes
(Google Search)]
[index]
(a)
Movement
of substances across membranes, with their concentration gradient (i.e., from
areas of high concentration to areas of low concentration) and via facilitation
by integral membrane proteins, is termed facilitated diffusion
(b)
[facilitated diffusion (MicroDude)] [index]
(a)
Movement
of substances across membranes, against their concentration gradient (i.e.,
from areas of low concentration to areas of high concentration) via
facilitation by integral membrane proteins, is termed active transport
(b)
Note
that active transport additionally is defined by a requirement for an
expenditure of energy
(c)
In
a very real sense, active transport consists of a pumping of substances across
membranes, thus increasing the
substance's concentration on one side of the membrane
(d)
[active transport (MicroDude)] [index]
(25) Cells are defined by the asymmetry of their membranes
(a)
A
cell functions in part as a consequence of the both the selective permeability
of its membrane and the asymmetry of its membrane
(b)
Asymmetry
means that the two sides of the membrane do not fully resemble each other—and
that the proteins associated with the membrane have a directionality so that
there is an unambiguous inside of a protein as well as an unambiguous outside
(c)
See Figure 4.7, The fluid
mosaic model of the cell membrane
(d)
Because
of the cell membrane's asymmetry, cells allow or pump into their cytoplasm
those substances they want to allow or pump in, and allow or pump out those
substances that they want to get rid of
(e)
Thus,
a cell with an intact plasma membrane automatically (though typically with some
expenditure of energy) carries out the processes necessary for the maintenance,
growth, and replication of the cell
(f)
[assymetry membrane
(Google Search)]
[index]
(a)
Osmosis
is the movement of water into a cell by simple diffusion
occurs from regions of high water concentration to regions of low water
concentration
(b)
Water's
concentration may be lowered by dissolving substances in it
(c)
The
more that is dissolved in a water solution, the lower the concentration of
water in that solution
(d)
Across
membranes, water naturally moves from regions of high water concentration to
regions of low water concentration
(e)
This
movement is termed osmosis
(f)
[osmosis -reverse, osmolarity, osmotic pressure, osmosis (Google Search)]
[osmotic pressure (MicroDude)] [index]
(a)
"Tonicity describes the behavior of cells
in a fluid environment."
(b)
Essentially,
there exist a series of terms that describe the solute concentration of a
solution relative to the concentration exhibited by a reference solution
(typically, outside of the cell relative to inside of the cell, with the latter
the reference):
(i)
Isotonic
(ii)
Hypotonic
(iii)
Hypertonic
(c)
See Figure 4.31, Experiments
that examine the effects of tonicity on osmosis
(d)
[tonicity and osmolarity
(Google Search)]
[illustration, tonicity] [index]
(a)
An
isotonic solution is one that has the same solute concentration as that
displayed by the solution inside of a reference cell that is found suspended in
the solution
(b)
[isotonic and microbiology
(Google Search)]
[osmosis in isotonic
environment] [index]
(a)
A
hypotonic solution is one that has a lower
solute concentration than the reference cell's cytoplasm
(b)
Red
blood cells suspended in a hypotonic solution may burst following their osmotic
uptake of water
(c)
Cells
with cell walls (including most bacteria, plants, and fungi) will resist taking
in water and therefore will resist bursting
(d)
[hypotonic and microbiology
(Google Search)]
[osmosis in hypertonic environment]
[index]
(a)
A
hypertonic solution is one that has a higher solute concentration than the
reference cell's cytoplasm
(b)
Red
blood cells suspended in hypertonic solutions tend to shrivel
(c)
[hypertonic and microbiology
(Google Search)]
[osmosis in hypotonic
environment] [index]
(31) Cytoplasm
(a)
The
cytoplasm is simply the region of a bacterial cell that is internal to the
plasma membrane
(b)
[cytoplasm and bacteria
(Google Search)]
[index]
NUCLEIC ACIDS, AND THEIR
PROTECTION
(a)
Ribosomes
are the organelles responsible for making proteins
(b)
[ribosome (Google Search)] [index]
(33) Nuclear region (nucleoid)
(a)
This
is simply where the bacterial DNA is located
(b)
The
nucleoid is not a membrane-enclosed
region
(c)
["nuclear region" and
bacteria, nucleoid and bacteria
(Google Search)]
[index]
(a)
An
endospore is a non-metabolizing bacterial cell that are highly resistant to
numerous environment degradants including heat, drying, and all sorts of
chemical insults
(b)
Not
all bacteria produce endospores
(c)
Endospores
are produced within bacterial cells (hence the endo- part of their name)
(d)
Sporulation
= endospore formation
(e)
Germination
= endospore conversion back to a vegetative (i.e., metabolizing/growing)
bacterial cell
(f)
Much
of the elaborate efforts employed to sterilize bacteria media or instruments is
employed to create conditions that are sufficiently harsh that even endospores
are killed (and hence the media or instrument has been sterilized)
(g)
[endospore (Google Search)] [endospore stain of genus Bacillus, endospore stain of Clostridium tetani, endospore cycle ß if you are having trouble understanding
just what exactly an endospore is, then follow this series of cartoons
depicting endospore formation (Biol 230 Microbiology – Gary E. Kaiser)] [“Jurassic Park” bacterium] [hey! better use a pressure cooker] [index]
BACTERIA EXTERNAL ANATOMY
(a)
Attached
to the cell envelope and projecting into the external environment are flagella
(b)
These
are long, thin, helical structures that are used like propellers to move
bacteria
(c)
See figure 4.13, Structure
of two different bacterial flagella
(d)
Note
that bacteria flagella and eucaryotic flagella are not structurally similar
(e)
Bacteria
can have from one to many flagella, depending on bacterial species or strain
(f)
See Figure 4.12,
Arrangements of bacterial flagella
(g)
(h)
[bacteria and flagella,
flagellar arrangements
(Google Search)]
[what the heck is a bacterium’s
tail? (Microbiology at KU and Jack's
Place] [index]
(a)
Bacteria
lacking flagella
(b)
[atrichous (not much
on bacteria out there) (Google Search)] [index]
(a)
Bacilli
with a single flagellum located at a pole
(b)
[monotrichous (Google Search)] [index]
(a)
Bacilli
with two flagella, one located at each pole
(b)
[amphitrichous (Google Search)] [index]
(a)
Bacilli
with two or more flagella located at a single end or two or more each located
at both ends (i.e., for former that would be at least two flagella and for the
latter that would be at least four flagella)
(b)
[lophotrichous (Google Search)] [index]
(a)
Bacilli
with many flagella all over their surface
(b)
[peritrichous (Google Search)] [image of peritrichous bacteria]
[index]
(41) Axial filaments (endoflagella)
(a)
Axial
filaments are the spirochete equivalent of flagellum
(b)
These
are in contact with the spirochete cell envelope over their entire length and
cause the entire spirochete bacterium to rotate and move as a corkscrew.
(c)
(d)
[axial filaments, endoflagella (Google Search)] [index]
(42) Chemotaxis (positive chemotaxis, negative chemotaxis)
(a)
Chemotaxis
is the movement toward or away from a chemical stimulus
(b)
This
occurs via a “random walk” consisting of runs in which flagella propel the
bacterium forward and twiddles in which opposite-turning flagella cause the
bacteria to tumble
(c)
Directed
movement occurs because runs are longer in the direction in which the bacterium
is attempting to move
(d)
Movement
towards a specific something an organism wants to mover towards is called positive
chemotaxis while movement away from a specific something an organism wants
to avoid is called negative chemotaxis
(e)
See Figure 4.14, Chemotaxis
(f)
(g)
[chemotaxis and bacteria
(Google Search)]
[index]
(a)
Movement
towards light = positive phototaxis; away = negative phototaxis
(b)
[phototaxis and bacteria
(Google Search)]
[index]
(a)
A
rigid, proteinaceous projection from the surface of bacterium that is used to
attach the bacterium to various surfaces
(b)
By
allowing adherence to cells and tissue the existence of pili allows bacteria to
be pathogenic against certain hosts (i.e., those organisms to which they can
attach)
(c)
(d)
[bacteria pili (Google Search)] [index]
(a)
Typically
polysaccharide-containing secretions that collect around the bacterial cell
surface
(b)
[glycocalyx (Google Search)] [index]
(a)
A well organized bacterial
glycocalyx that is firmly attached to the bacterial cell wall
(b)
By
protecting bacteria from host defenses capsules can contribute to the
pathogenicity
(c)
[bacterial capsule (Google Search)] [index]
(a)
Slime
layers are a more-diffuse glycocalyx than capsules
(b)
Slime
layers protects cells from drying, serve to trap nutrients, or may bind cells
together
(c)
For
example, Slime layers can trap nutrients and water, acting, for example, as a
seal over a nutritious substrate, thus allowing a bacteria to use exoenzymes
(extracellular enzymes) in a limited area containing high concentrations of
substrate (i.e., to-be-digested nutrients)
(d)
[slime layer (Google Search)] [index]
(48) Vocabulary [index]
(a)
Active
transport
(b)
Amphitrichous
(c)
Atrichous
(d)
Axial
filaments
(e)
Bacillus
(f)
Bacterial cell arrangements
(g)
Bacterial cellular anatomy
(h)
Bacterial
shapes
(i)
Capsule
(j)
Cell
wall
(k)
Cells are defined by the
asymmetry of their membranes
(l)
Chemotaxis
(n)
Coccobacillus
(o)
Coccus
(p)
Cytoplasm
(r)
Domains
(s)
Endoflagella
(t)
Endospores
(v)
Endotoxin
(w)
Eukaryotes
(y)
Flagella
(z)
Glycocalyx
(cc)
Hypertonic
(dd)
Hypotonic
(ee)
Inner
membrane
(ff)
Isotonic
(gg)
Lipopolysaccharide
(hh)
Lophotrichous
(ii)
LPS
(jj)
Monotrichous
(kk)
Movement across membranes
(ll)
Negative chemotaxis
(mm)
Nuclear
region
(nn)
Nucleoid
(oo)
Osmosis
(pp)
Outer
membrane
(qq)
Periplasm
(rr)
Periplasmic space
(ss)
Peritrichous
(tt)
Phototaxis
(uu)
Pili
(vv)
Plasma
membrane
(ww)
Pleomorphic
(xx)
Positive chemotaxis
(yy)
Prokaryotes
(zz)
Protoplast
(aaa)
Ribosomes
(bbb)
Sarcina
(ccc)
Size of prokaryotes
(ddd)
Slime
layer
(eee)
Spheroplast
(fff)
Spirillum
(ggg)
Spirochete
(hhh)
Staphylo-
(iii)
Strepto-
(jjj)
Tetrad
(kkk)
Tonicity