Seemingly simple in structure and markedly different from eukaryote
and protist organisms, many scientists believe prokaryotic cells were amongst
the first on the Earth and very well may out-survive all other organisms.
Prokaryotes are, with few exceptions,
unicellular organisms; many bacteria live in colonies, making them appear
larger at first glance, but individual cells are visible under a microscope.
These cells do not possess membrane-based organelles, but the fundamentals of
cell theory still apply.
proposed by German scientists Matthias Schleiden and Theodor Schwann, and later
amended by Rudolf Virchow, four basic rules apply to eukaryotic, prokaryotic
and protist cells:
forms of life contain one or more cells
cells come from pre-existing cells
functions that make life possible occur within the boundaries of cells
cells possess genetic material required to regulate cell functions and
replicate, passing this genetic information to new cells
have expanded and refined cell theory with the advent of advanced microscopy
instruments, but these basic rules still apply to all cells.
vs. Eukaryotes – Similarities?
cells, like those in eukaryotic uni- and multi- cellular organisms contain
ribosomes and DNA – genetic matter that control all cell functions, including
cells require energy to survive and undergo chemical processes to sustain life.
Biochemical processes often involve the use of carbohydrates, proteins, lipids
and nucleic acids for cell functions such as:
food into usable energy
processes essential to the life – acquisition of energy, reproduction – are
similar in prokaryotic and eukaryotic cells, regardless of the difference in
structure and means.
Prokaryotes vs. Eukaryotes – Differences
as well as protists, a miscellany group made up of eukaryote-like plant, animal
and fungi missing one or more characteristics to be defined as purely
eukaryotic, differ greatly from prokaryotes
significant is the lack of a nucleus in prokaryotic cells as well as
membrane-based organelles found in all eukaryotic cells.
have DNA, but eukaryote-DNA contain histones and chromosomes in a linear
Mitochondria (or the plant equivalent chloroplasts) is one of the
many membrane-bound organelles present in eukaryotes, along with:
addition, while eukaryotes can be uni- or multi- cellular, heterotroph or
autotroph, prokaryotes are heterotrophic
The Prokaryotic Cell
from two to five micrometers (um), typical prokaryotic cell structure includes:
Wall – lends to the shape of the cell; two types are gram positive and gram
– hair-like projections surrounding the outer layer of the cell; enables bacteria
to stick-on surfaces or latch-on other cells
– thick covering of the cell wall that can provide protection from phagocytosis,
chemicals and dehydration; the sticky nature allows it to adhere to other
cells; found in gram-positive bacteria and blue-green algae
– attached to the cell wall, usually described as “whip-like;" most prokaryotes
are in constant motion and only able to move forward and backward
Membrane – a thin, flexible asymmetrical “sac" that essentially contains the
cell; serves as a passageway for anything that enters or leaves the cell such
as nutrients and gases; also holds the cytoplasm
– can be compared, in terms of purpose, as carrying out similar functions to
membrane-bound organelles; contains enzymes for and carries out metabolism;
important to note that nothing within the cytoplasm is separated via membrane
or well-defined sections, items are suspended in the semi-fluid gel
– tiny rings of DNA that can be transferred to other cells; anti-biotic
resistance is a prime illustration of the way prokaryotes share information with other prokaryote cells, enabling
cells to make adjustments that ensure survival
– combination of RNA and protein, the function of prokaryotic ribosomes widely
depends on the bacteria
Prokaryotes consist of two Kingdoms:
Monera or Bacteria (sometimes called eubacteria), which includes cyanobacteria
noted for the ability to carry out photosynthesis, and Archaea (archaebacteria).
With the greatest ability to withstand the most severe environmental
conditions, science believes the latter contains the oldest cells/organisms on
the planet, and sometimes referring to it as “ancient bacteria."
study of prokaryotic cells involves the study of bacteria – single cells that
can be as tiny as two microns and look like dots under a compound microscope.
Bacteria are fascinating subjects for many reasons:
of purpose – without the existences of many “good" bacteria, many species could
not exist, including humans
found everywhere – bacteria are not limited to causing disease, for example,
human intestines to help with digestion
in the digestive process of rudiment animals
decompose waste material
– some bacteria create endospores, enabling them to survive if placed in a
different or “harsh" environment
survive conditions that would kill other cells – for example, some live in
exceptionally hot or cold temperatures, gaseous environments or in places with
intense high or low Ph
– even though the cell structure seems simple, especially when compared to
eukaryotes, unicellular bacteria and archaea organisms not only perform complex
functions to survive, they are the oldest known cells
– many bacteria grow in colonies, yet each cell maintains its autonomy
– cells pass along genetic information via a process called binary fission;
cells create duplicate DNA and divide
Prokaryotes are classified through
characteristics such as shape, behavior, size, growth, and stains.
are separated into three classes based on shape: cocci, bacilli, and spirilla.
Although defined by morphology, they might not fall into the same
classification – the only commonality might be shape.
Also important to note,
due to the size of bacteria, shapes are the only aspects visible under a light
microscopes, such as electron microscopes, which offer more powerful
magnification, in order to see the internal structures of the cell.
are described as round, flat spheres and can be observed as lone cells, pairs,
chains, tetrads (4 cells), clusters or cubes (8 cells); streptococcus is a
chain of cocci-shaped bacteria cells responsible for the common sore throat
sometimes described as cylindrical and called as bacilli exist as singles,
pairs and chains; unlike the simpler cocci, the length of chains has no bearing
known for their spiral shape can appear as one curve, like elbow-macaroni,
twists or genuine spirals
way bacteria behaves is also important in identification; attributes include:
a culture grows in a warm or cold environment
behavior when exposed to a variety of filters, chemicals, elements, gases or
states (i.e., dehydration, change in Ph)
(i.e., observing sample in a Petri-dish over time, possibly changing the
cells are especially intriguing to individuals interested in microbiology and
Although shapes can be discerned under a compound microscope, powerful
electron microscopes are required to observe internal details of the cell. Separated
into Kingdoms Monera and Archaea, prokaryotes
consist primarily of bacteria cells.
from 2-5 um, these impressive one-celled organisms survived millions of years;
notorious for the result of diseases, most eukaryotic organisms could not exist
without “good" bacteria – including humans.
Using microscopy, researchers try
to understand their ability to adapt and survive, the way they help the human
body and how to use them to improve the earth.
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