Defined as pre-nucleus, prokaryotes are cells that contain no membrane-based organelles, including a nucleus.
Mostly recognized as bacteria, two prokaryotic kingdoms exist: Monera or Bacteria and Archaea.
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.
Initially 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:
Scientists have expanded and refined cell theory with the advent of advanced microscopy instruments, but these basic rules still apply to all cells.
Prokaryotic cells, like those in eukaryotic uni- and multi- cellular organisms contain ribosomes and DNA – genetic matter that control all cell functions, including replication.
All 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:
Elemental processes essential to the life – acquisition of energy, reproduction – are similar in prokaryotic and eukaryotic cells, regardless of the difference in structure and means.
Eukaryotes 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 in structure.
Most significant is the lack of a nucleus in prokaryotic cells as well as membrane-based organelles found in all eukaryotic cells.
Both have DNA, but eukaryote-DNA contain histones and chromosomes in a linear structure. Mitochondria (or the plant equivalent chloroplasts) is one of the many membrane-bound organelles present in eukaryotes, along with:
In addition, while eukaryotes can be uni- or multi- cellular, heterotroph or autotroph, prokaryotes are heterotrophic single-celled organisms.
Ranging from two to five micrometers (um), typical prokaryotic cell structure includes:
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.”
The 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:
· Range of purpose – without the existences of many “good” bacteria, many species could not exist, including humans
· Are found everywhere – bacteria are not limited to causing disease, for example, they:
· Adaptability – some bacteria create endospores, enabling them to survive if placed in a different or “harsh” environment
· Can 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
· Function – 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
· Colonization – many bacteria grow in colonies, yet each cell maintains its autonomy
· Reproduction – 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.
Bacteria 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.
The way bacteria behaves is also important in identification; attributes include:
In addition, bacteria are separated into gram positive and gram negative, easily discerned from one another by the use of a stain.
Prokaryote cells are especially intriguing to individuals interested in microbiology and microscopy.
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.
Ranging 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.
See Also: Bacteria under the Microscope
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