Important words and concepts from Chapter 27,
Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu)
for Biology 113 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: Prokaryotes and the
Origins of Metabolic Diversity
(a)
"The history of prokaryotic life is
a success story spanning at least 3.5 billion years. Prokaryotes were the
earliest organisms, and they lived and evolved all alone on Earth for 2 billion
years. They have continued to adapt and flourish on an evolving Earth, and in
turn they have helped to change the Earth."
(b)
[prokaryotes and the origins of
metabolic diversity (Google Search)]
[index]
(a)
The impact of prokaryotes is vast with prokaryotes
responsible for either all or significant portions of all of the following
(i)
Nutrient (re)cycling
(ii)
Decomposition
(iii)
Disease
(iv)
Inventors of biochemical pathways
(v)
Extreme biochemical diversity
(vi)
Producers of oxygen
(vii)
Consumers of oxygen
(viii)
Progenitors of eukaryotes
(ix)
Symbionts
(x)
Endosymbionts
(b)
Arguably, eukaryotes could not survive the loss of
all the world's free living prokaryotes, though one could readily imagine a
world consisting solely of prokaryotes. Such a world, in fact, would be
equivalent to that which existed prior to the rise of the eukaryotic lineage, a
span which includes a majority of the time on earth during which life existed
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Impact of Prokaryotes (supplemental discussion) ·
Earliest cells ·
Inventors of biochemical pathways (a)
Heterotrophs (b)
Autotrophs (c)
Chemotrophs (d)
Phototrophs ·
Extreme biochemical diversity (a)
Ditto (above) ·
Nutrient (re)cycling (a)
Mineralization (b)
Nitrogen fixing / denitrification ·
Decomposition (a)
Mineralization ·
Disease (infectious) (a)
Endotoxins / exotoxins ·
Symbionts (a)
Commensalism (b)
Mutualism (c)
Parasitism (infectious disease) ·
Producers of oxygen (a)
Cyanobacteria (b)
But not purple and green nonsulfur ·
Consumers of oxygen (but not all) (a)
Aerobes (b)
Obligate aerobes (c)
Anaerobes (d)
Obligate anaerobes (e)
Facultative anaerobes ·
Progenitors of Eukaryotes ·
Endosymbionts |
(c)
[“impact of prokaryotes”, impact
of prokaryotes (Google Search)]
[index]
(3) Prokaryotic morphological diversity
(a)
Bacteria come in a variety of shapes though
typically one finds
(i)
Cocci (spheres)
(ii)
Bacilli (rods)
(iii)
Spirals
(b)
See Figure 27.3, The most
common shapes of prokaryotes
(c)
Most bacteria occur as individual cells but there
also exist numerous examples of bacteria that exist within arrangements with
other bacterial cells of the same species (i.e., linked together)
(d)
A few bacteria even display differentiation within these groupings of
cells; some degree of differentiation within colonies of cells represents
multicellularity at its most primitive
(e)
[bacterial shapes (MicroDude)] [prokaryotes morphological diversity (Google Search)]
[bacterial architecture: the
virtual bacterium (Microbiology 101/102
– Washington State University)] [index]
(4) Cell envelopes (Gram-negative cell wall, Gram-positive cell wall)
(a)
Among the eubacteria there exist two fundamental types of cell
envelopes termed Gram-positive and Gram-negative
(b)
Both have cell walls that consist of peptidoglycan (a characteristic of
eubacteria but not archaebacteria cell walls)
(c)
The Gram-positive cell wall
is thicker and is not surrounded by a second membrane
(d)
The Gram-negative cell wall
is thinner and is surrounded by a
second membrane (termed outer membrane)
(e)
Note that Gram-negatives tend to the more pathogenic (disease causing) though certainly there are a large number of
Gram-positives among pathogenic bacteria
(f)
See Figure 27.5,
Gram-positive and gram-negative bacteria
(g)
Basically, Gram-positives make more effective use of exoenzymes, digesting nutrients surrounding cells, and then
absorbing the digestive products
(h)
Gram-negatives, on the other hand, are better at protecting themselves
while causing disease, but are at the same time more dependent on the existence
of predigested nutrients in their environment
(i)
(external to cell envelopes there exist additional bacterial structures
including capsules, pili, and flagella)
(j)
See Figure 27.6, Pili
(k)
[capsule (MicroDude)] [flagella (MicroDude)] [pili
(MicroDude)] [peptidoglycan (Google Search)]
[index]
(a)
The most common form of bacterial motility is effected by bacteria flagella
(b)
These are propeller-like appendages that are morphologically unlike the
flagella found in eukaryotes
(c)
Basically, bacterial flagella are whip-like appendages that are spun to
effect forward thrust through viscous liquid media
(d)
See Figure 27.7, Form and
function of prokaryotic flagella
(e)
[motility, bacteria flagella (Google Search)]
[flagella (MicroDude)] [index]
(6) Taxis (positive taxis, negative taxis, chemotaxis,
phototaxis)
(a)
Bacteria are able to move up and down gradients
via their employment of flagella
(b)
This is accomplished not by their steering themselves in a specific
direction, but instead by their interspersing movement with random tumbling; by
moving for longer periods when heading in the direction they want to head in,
they bias their movement in that direction (essentially a biased random walk)
(c)
Movement towards or away from a stimulus is termed taxis
(d)
Movement toward a specific chemical (up its concentration gradient) is
termed positive chemotaxis
(e)
Movement away from a specific chemical (down its concentration
gradient) is termed negative chemotaxis
(f)
Movement toward light is termed positive phototaxis
(g)
[positive taxis, negative taxis, chemotaxis, phototaxis (Google Search)]
[index]
(a)
(b)
Recall additionally that the bacterial chromosome
is found as a double-stranded circle (while the eukaryotic chromosome is double-stranded, but linear)
(c)
The bacterial chromosome does tend to be confined to a compact region
within the bacterial cytoplasm termed the nucleoid region; “n”
marks the nucleoid regions these electron micrographs
of diplococci à
(d)
Recall that bacteria also have plasmids which are
also double-stranded, circular pieces of DNA, but which tend to contain genes which are expendable to the bacteria except in certain
environments (e.g., antibiotic resistance genes)
(e)
[nucleoid (Google Search)]
[(Nucleoid structure and
localization in Sulfolobus species) (The Archaea Group)]
[index]
(8) Bacterial growth
(a)
Recall that bacteria grow via a non-mitotic or meiotic process known as binary fission
(b)
”The word growth as applied
to bacteria actually refers more to the multiplication of cells and population
growth than to the enlargement of individual cells. The conditions for optimal
growth—temperature, pH, salt concentrations, nutrient sources, and so on—vary
according to species."
(c)
Variations in environmental conditions away from optimal for a
species of bacteria tends to result in a lack of bacterial growth including
such things as
(i)
(ii)
Absence of proper nutrients
(iii)
Relative lack of water
(iv)
High salt concentrations
(v)
Extremes in pH
(d)
Lack of growth for many bacteria tends to lead to subsequent cell death
(e)
Other bacteria are capable of forming extremely stable states under
adverse conditions; these are know as endospores, the
bacterial equivalent to a bomb shelter
(f)
Endospores forming within bacilli à
(g)
[growth and culturing of bacteria (MicroDude)] [(Google
Search)] [index]
(a)
Describing an organism in terms of its nutritional patterns tends to
focus on the sources of two key items
(i)
Energy
(ii)
Carbon
(b)
All other nutrients, necessary as they may be, are essentially just
details
(c)
There exist two energy requirement types
(ii)
Chemotrophs
(d)
There exist two carbon requirement types
(i)
Autotrophs
(ii)
Heterotrophs
(e)
There exist examples among microbes of all four combinations
(i)
Photoautotrophs
(ii)
Photoheterotrophs
(iii)
Chemoautotrophs
(iv)
Chemoheterotrophs
(f)
See Table 27.1, Major
nutritional modes
(a)
Phototrophs obtain their energy from photons
(b)
[phototrophs (Google Search)]
[index]
(a)
Chemotrophs obtain their energy from reduced
chemical bonds
(b)
Note that the compounds supplying these reduced chemical bonds are not
necessarily organic compounds
(c)
[chemotrophs (Google Search)]
[index]
(a)
Autotrophs obtain their carbon from CO2
(b)
Another term for autotroph is "self feeder"
(c)
Another term for autotroph is "primary producer"
(d)
[autotrophs (Google Search)]
[index]
(a)
Hetertrophs obtain their carbon from organic
sources, i.e., they eat other organisms
(b)
Another term for heterotroph is "consumer"
(c)
[heterotrophs (Google Search)]
[index]
(a)
An organism which gets its energy from light
and its carbon from CO2
(b)
Examples include
(i)
Green plants
(ii)
Algae
(iii)
Cyanobacteria
(c)
The photoautotrophs are additionally the generators of molecular oxygen
(d)
[photoautotroph (MicroDude)] [(Google
Search)] [index]
(a)
Not all photosynthetic organisms are capable of carbon fixing all of
their carbon
(b)
Those that must obtain carbon in a reduced form (i.e., other than as CO2)
are termed photoheterotrophs
(c)
Certain bacteria are the sole photoheterotrophs
(d)
Note that photoheterotrophs probably represent a more primitive form of
photosynthetic
metabolism
(e)
[photoheterotroph (MicroDude)] [(Google Search)]
[index]
(a)
A chemoheterotroph is an organism that gets
its carbon from CO2 but its energy from reduced chemical bonds
(b)
For chemoautotrophs, as with photoautotrophs,
energy and carbon are not derived from the same sources
(c)
Instead, chemoautotrophs obtain their energy from reduced, non-organic
(not carbon-containing) compounds
(d)
Such compounds are found in such places as deep-sea hydrothermal vents
where, since there is no light, chemoautotrophic bacteria represent the producers
(e)
[chemoautotroph (MicroDude)] [(Google Search)]
[index]
(a)
Chemoheterotrophs tend to get their carbon and energy from the same source (e.g., glucose)
(b)
These are the more familiar of nutrient patterns and is found among
(i)
Animals
(ii)
Fungi
(iii)
Protists
(iv)
Most bacteria
(v)
Almost all cellular pathogens
(c)
"There is such a diversity of chemoheterotrophs that almost any
organic molecule can serve as food for at least some species."
(d)
[chemoautotroph (MicroDude)] [(Google
Search)] [index]
(18) Nitrogen metabolism (denitrification,
nitrogen fixing)
(a)
Together, bacterial species are very adept at metabolizing different
forms of nitrogen, far more adept than are the sum of the eukaryotes
(b)
Nitrogen fixing is the conversion of
atmospheric nitrogen (N2) into bioavailable nitrogen (e.g., NH3,
ammonia)
(c)
Denitrification is the conversion of
non-atmospheric nitrogen (nitrate and nitrite, NO3- and
NO2-) to N2 (thus making the nitrogen no
longer bioavailable except to nitrogen fixers); note that the process by which
denitrification occurs is known as anaerobic respiration, cellular respiration in which something other
than molecular oxygen is reduced as the final electron acceptor
(d)
"In terms of nutrition, nitrogen-fixing cyanobacteria are the most self-sufficient of all organisms.
They are photoautotrophs that require only light energy, CO2,
N2, water, and some
minerals in order to grow."
(e)
[denitrification (Google Search)]
[nitrogen fixing (Google Search)]
[nitrogen sources (MicroDude)] [index]
(19) Oxygen requirements (obligate
aerobes, facultative anaerobes, obligate anaerobes)
(a)
Some organisms require molecular oxygen (O2) to stay alive;
these are called obligate aerobes, e.g., animals as well as numerous bacteria
(b)
Other organisms can do without molecular oxygen but can make use of
molecular oxygen if it is available; these are called facultative anaerobes, e.g., bakers yeast and
bacteria such as Escherichia coli
(c)
Yet additional organisms cannot survive in the presence of molecular
oxygen; these are called obligate anaerobes
and include, for example, a number of exotoxins producers of the Clostridium genera (e.g., the bacteria responsible for
botulism, tetanus, and gas gangrene)
(d)
[oxygen requirements (MicroDude)] [(Google
Search)] [index]
(20) Evolution of metabolic pathways (supplemental
discussion)
(a)
"All forms of nutrition and nearly all metabolic pathways evolved
among prokaryotes before eukaryotes arose. As early prokaryotes evolved, they were
constantly changing physical and biological environments. In response to these
changes, new metabolic capabilities evolved that, in turn, changed the
environment faced by the next community of prokaryotes."
(b)
Metabolic pathways probably evolved in steps, where the first step to
evolve was the utilization of the end product
(c)
That is, the environment in which life evolved must have supplied all
necessary nutrients and thus early "life" required no synthesis
capabilities beyond those involved in the combination of nutrients into novel
molecules
(d)
Key among those nutrients presumably was an energy currency, e.g., ATP
or, instead, pyrophosphate
(e)
When a key nutrient was no longer available (because organisms utilized
it faster than it could be replenished abiotically), organisms would come to
dominate if they were able to synthesize the no-longer-available nutrient by
modifying a still-available nutrient
(f)
The next nutrient up this ladder would then be depleted, with selective
advantage going to the organisms that could either synthesize the first
nutrient by a different means, or could synthesize the second nutrient by
modifying a still available nutrient, and so on
(g)
Obviously, all of this evolving probably took a very long time
(h)
A core metabolic pathway which probably remains from (i.e., dates back
to) these days of metabolic experimentation is glycolysis
(i)
In addition to simply evolving more and more elaborate ways of doing
basically the same thing, organisms could co-opt existing metabolic pathways to
do things other than producing the stuff for which these existing pathways
evolved
(j)
Thus, metabolic evolution involves
(i)
Increasing the kinds of substrates from
which key molecules may be synthesized
(ii)
Elaboration on metabolic pathways to produce molecules other than those
for whose synthesis the pathway evolved in the first place
(k)
Your text additionally speculates that such things as chemiosmosis and photosynthesis evolved from processes that
served to protect the organism from toxic substances (e.g., excessive hydrogen
ions or light), chemiosmosis and photosynthesis serving simply as means of
tapping into the energy potentials created by concentrating these substances or
their associated energy
(l)
[evolution of metabolism
(Google Search)]
[index]
(21) Archaebacteria metabolism (methanogens, extreme
halophiles, extreme thermophiles, sulfur-metabolizing bacteria)
(a)
Archaebacteria are unusual in terms of the environments in which they
live, the substrates they consume, and the products they
release
(b)
Included among archaebacteria are
(i)
Mathanogens, which release methane as a metabolic waste product, thus
producing marsh gas and flatulence from cellulose consuming herbivores (e.g.,
cattle, termites) [methanogens (Google Search)]
(ii)
Extreme halophiles, organisms which live in extremely salty
environments such as inland seas [extreme halophiles
(Google Search)]
(iii)
Extreme thermophiles, organisms which live in extremely hot environments
including
(iv)
Various sulfur-metabolizing bacteria [sulfur-metabolizing bacteria
(Google Search)]
(c)
Archaebacteria are also found in less extreme environments but those
species of archaebacteria have not been studied as extensively as
archaebacteria that live in extreme environments (
(d)
See Figure 27.2, The three domains
of l
(e)
See Figure 27.13, Some major
groups of prokaryotes
(f)
See Table 27.2, A comparison
of the three domains of life
(g)
[archaebacteria, archaeobacteria (note alternative spelling), archaebacteria metabolism
(Google Search)]
[index]
(22)
Symbiosis (host, symbiont)
(a)
Microbes are often involved in symbiotic relationships with other
organisms, including other microbes
(b)
A symbiosis is a close (i.e., intimate) relationship between two or
more organisms that lasts over a reasonably long span of one or both lives
(c)
Note that the long-term aspect of symbiosis precludes the inclusion of
such things as predation from the realm of symbiosis
(d)
In a symbiosis between a microbe and a large organism, the microbe is
typically considered the symbiont and the larger organism is the host
(e)
Symbiotic relationships are defined typically in terms of the degree of
harm, or help, one partner does to the other, as
(i)
Mutualism
(ii)
Commensalism
(iii)
Parasitism
(f)
[symbiosis and bacteria
(Google Search)]
[index]
(a)
In mutualism both symbiont and host benefit
(b)
[mutualism, mutualism and bacteria
(Google Search)]
[index]
(a)
Commensalism is a symbiosis in which
one organism benefits while the other is neither helped nor harmed
(b)
[commensalism, commensalism and bacteria (Google Search)]
[index]
(a)
Parasitism is a symbiosis in which one organism is hurt
(typically the host) and the other organism is helped (the symbiont, here,
a.k.a., the parasite)
(b)
[parasitism, parasitism and bacteria
(Google Search)]
[index]
(a)
Diseases caused by microbes typically are a consequence of either a parasitic
symbiosis
or the exposure of an organism to a toxic product of a
microbe
(b)
During parasitism, the host typically is harmed as its
interests clash with those of the parasite
(c)
In particular, the parasite tends to either steal food from the host or
eat the tissues of the host
(d)
In addition, various attempts the parasite makes to keep from being
destroyed by the host can also harm the host
(e)
Two chemical mechanisms by which bacterial parasites harm their hosts
are the release of exotoxins
and the release of endotoxins
(f)
[endotoxin (MicroDude)] [infectious disease
(Google Search)]
[index]
(a)
Exotoxins are substances that bacteria (typically Gram-positive)
release that do the host harm (though they are also employed by Gram-negative pathogens, thye are
observed among Gram-negatives to a lesser degree than among Gram-positives)
(b)
Very often these substances are enzymes involved in
the destruction of host tissue
(c)
The symptoms associated with exposure to different
exotoxins vary with the exotoxin
(d)
Exotoxins include some of the most powerful toxins known, including
botulism toxin
(e)
[exotoxins (MicroDude)] [(Google Search)]
[index]
(a)
Endotoxin is a component of the Gram-negative outer membrane (and
not an enzyme)
(b)
The body uses the presence of endotoxin as a signal that a
Gram-negative infection is going on
(c)
(d)
Since antibiotic treatment can result in
bacterial cell breakdown and subsequent endotoxin release, the treatment of
severe Gram-negative infections (e.g., septicemia) is very
difficult, since killing the organism can lead to a worsening of symptoms
(e)
This is what endotoxin (lipid A of LPS)
looks like (note the long hydrocarbon tails towards the bottom of the structure
that serve to anchor LPS into the Gram-negative outer membrane—no, you are not
responsible for knowing this structure) à
(f)
[endotoxin (MicroDude)] [septic shock (Google Search)]
[index]
(29)
Vocabulary [index]
(b)
Autotrophs
(c)
Bacterial growth
(d)
Cell envelopes
(e)
Chemoautotroph
(f)
Chemoheterotroph
(g)
Chemotaxis
(h)
Chemotrophs
(i)
Commensalism
(j)
Endotoxin
(k)
Exotoxins
(o)
Flagella
(p)
Denitrification
(t)
Heterotrophs
(u)
Host
(w)
Methanogens
(y)
Motility
(z)
Mutualism
(aa)
Negative taxis
(bb)
Nitrogen
fixing
(cc)
Nitrogen metabolism
(dd)
Nutritional patterns
(ee)
Obligate aerobes
(ff)
Obligate anaerobes
(gg)
Oxygen requirements
(hh)
Parasitism
(ii)
Photoautotroph
(jj)
Photoheterotroph
(kk)
Phototaxis
(ll)
Phototrophs
(mm)
Positive taxis
(nn)
Prokaryotic morphological diversity
(oo)
Sulfur-metabolizing bacteria
(pp)
Symbiont
(qq)
Symbiosis
(rr)
Taxis