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
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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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