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)