Prokaryotic cell | Eukaryotic cell |
Size of the cell is generally small(1- 10 µm) | Size of the cell is generally large (5- 100µm) |
The nuclear region is poorly defined, not bound by membrane. | Nuclear region is well defined, bounded by nuclear membrane. |
The undefined nuclear region containing only nucleic acid is called nucleoid. | Nuclear region consist of both histones (proteins ) and nucleic acid. |
Single chromosome is present. | Many chromosomes are present. |
Membrane-bound organelles are absent | Membrane-bound organelles are present |
Nucleolus absent | Nucleolus present |
Prokaryotic cells are found in prokaryotic organisms ( bacteria) such as blue green algae. | Eukaryotic cells are found in eukaryotic organisms such as fungi, plants and animals. |
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Prokaryotic cells:
Eukaryotic cells:
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Pro = “before”, karyon = “nucleus” Prokaryotes, the first living organisms to evolve, are primarily distinguished by the fact that they lack a membrane-bound nucleus. In fact, the only membrane in prokaryotic cells is the plasma membrane--the outer boundary of the cell itself. Their genetic material is naked within the cytoplasm, ribosomes their only type of organelle. Prokaryotes are most always single-celled, except when they exist in colonies. These ancestral cells, now represented by members of the domains Archaea and Eubacteria, reproduce by means of binary fission, duplicating their genetic material and then essentially splitting to form two daughter cells identical to the parent. Features of Eukaryotes Eu = “true”, karyon = “nucleus” The most noticeable feature that differentiates these more complex cells from prokaryotes is the presence of a nucleus, a double membrane-bound control center separating the genetic material, DNA (deoxyribonucleic acid), from the rest of the cell. In addition to the plasma membrane, eukaryotic cells contain internal membrane-bound structures called organelles. Organelles, such as mitochondria and chloroplasts, are both believed to have evolved from prokaryotes that began living symbiotically within eukaryotic cells. These vital organelles are involved in metabolism and energy conversion within the cell. Other cellular organelles within eukaryotic cell structure carry out the many additional functions required for the cell to survive, thrive, grow and reproduce. Eukaryotic cells can reproduce in one of several ways, including meiosis (sexual reproduction) and mitosis (cell division producing identical daughter cells).Features of Prokaryotes
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Part of our definition/description of what it means to be a living thing on Earth includes the assertion that living things are made of cells and cell products. In other words, we consider the cell to be a pretty fundamental structural aspect of life. Cells in our world come in two basic types, prokaryotic and eukaryotic. "Karyose" comes from a Greek word which means "kernel," as in a kernel of grain. In biology, we use this word root to refer to the nucleus of a cell. "Pro" means "before," and "eu" means "true," or "good." So "Prokaryotic" means "before a nucleus," and "eukaryotic" means "possessing a true nucleus." This is a big hint about one of the differences between these two cell types. Prokaryotic cells have no nuclei, while eukaryotic cells do have true nuclei. This is far from the only difference between these two cell types, however. Here's a simple visual comparison between a prokaryotic cell and a eukaryotic cell: This particular eukaryotic cell happens to be an animal cell, but the cells of plants, fungi and protists are also eukaryotic. Despite their apparent differences, these two cell types have a lot in common. They perform most of the same kinds of functions, and in the same ways. Both are enclosed by plasma membranes, filled with cytoplasm, and loaded with small structures called ribosomes. Both have DNA which carries the archived instructions for operating the cell. And the similarities go far beyond the visible--physiologically they are very similar in many ways. For example, the DNA in the two cell types is precisely the same kind of DNA, and the genetic code for a prokaryotic cell is exactly the same genetic code used in eukaryotic cells. Some things which seem to be differences aren't. For example, the prokaryotic cell has a cell wall, and this animal cell does not. However, many kinds of eukaryotic cells do have cell walls. Despite all of these similarities, the differences are also clear. It's pretty obvious from these two little pictures that there are two general categories of difference between these two cell types: size and complexity. Eukaryotic cells are much larger and much more complex than prokaryotic cells. These two observations are not unrelated to each other. If we take a closer look at the comparison of these cells, we see the following differences: Examination of these differences is interesting. As mentioned above, they are all associated with larger size and greater complexity. This leads to an important observation. Yes, these cells are different from each other. However, they are clearly more alike than different, and they are clearly evolutionarily related to each other. Biologists have no significant doubts about the connection between them. The eukaryotic cell is clearly developed from the prokaryotic cell. One aspect of that evolutionary connection is particularly interesting. Within eukaryotic cells you find a really fascinating organelle called a mitochondrion. And in plant cells, you'd find an additional family of organelles called plastids, the most famous of which is the renowned chloroplast. Mitochondria (the plural of mitochondrion) and chloroplasts almost certainly have a similar evolutionary origin. Both are pretty clearly the descendants of independent prokaryotic cells, which have taken up permanent residence within other cells through a well-known and very common phenomenon called endosymbiosis. One structure not shown in our prokaryotic cell is called a mesosome. Not all prokaryotic cells have these. The mesosome is an elaboration of the plasma membrane--a sort of rosette of ruffled membrane intruding into the cell. This diagram shows a trimmed down prokaryotic cell, including only the plasma membrane and a couple of mesosomes. A mitochondrion is included for comparison: The similarities in appearance between these structures are pretty clear. The mitochondrion is a double-membrane organelle, with a smooth outer membrane and an inner membrane which protrudes into the interior of the mitochondrion in folds called cristae. This membrane is very similar in appearance to the prokaryotic plasma membrane with its mesosomes. But the similarities are a lot more significant than appearance. Both the mesosomes and the cristae are used for the same function: the aerobic part of aerobic cellular respiration. Cellular respiration is the process by which a cell converts the raw, potential energy of food into biologically useful energy, and there are two general types, anaerobic (not using oxygen) and aerobic (requiring oxygen). In practical terms, the big difference between the two is that aerobic cellular respiration has a much higher energy yield than anaerobic respiration. Aerobic respiration is clearly the evolutionary offspring of anaerobic respiration. In fact, aerobic respiration really is anaerobic respiration with additional chemical sequences added on to the end of the process to allow utilization of oxygen (a very common evolutionary pattern--adding new parts to old systems). So it's pretty reasonable of biologists to think that a mitochondrion evolved from a once-independent aerobic prokaryotic cell which entered into an endosymbiotic relationship with a larger, anaerobic cell. So is there any real evidence that the distant ancestors of mitochondria were independent cells? Quite a lot, actually. And of a very convincing type. Mitochondria (and chloroplasts, for that matter) have their own genetic systems. They have their own DNA, which is not duplicated in the nucleus. That DNA contains a number of the genes which are necessary to make the materials needed for aerobic cellular respiration (or photosynthesis, in the case of the chloroplast). Mitochondrial and chloroplast DNA molecules are naked and circular, like prokaryotic DNA. These organelles also have their own population of ribosomes, which are smaller and simpler than the ribosomes out in the general cytoplasm. Mitochondria and chloroplasts also divide on their own, in a manner similar to the binary fission of prokaryotic cells. Then there's that interesting outer membrane, another feature chloroplasts share with mitochondria. The manners by which large objects enter cells automatically create an outer membrane (actually a part of the big cell's plasma membrane) around the incoming object. This discussion suggests a very interesting question. Endosymbiosis is a very widespread phenomenon. The more we look, the more examples we find throughout the kingdoms of life. So, if a mitochondrion is the distant descendent of an independent prokaryotic cell, is it then an organism living inside a larger cell? Or is it just a part of that larger cell? Is it an independent organism or not? Before you leap to a conclusion, think a bit. Certainly, mitochondria are absolutely dependent upon the cells in which they reside. Like any long-time endosymbiont, they long ago gave up many of the basic life processes needed for independent life. And the cells in which they reside are completely dependent upon their mitochondria, because the anaerobic respiration they could do without the mitochondria wouldn't provide nearly enough energy for the cell's needs. In fact, it's very probable that the evolution of big, complex eukaryotic cells wasn't possible until the "invention" of aerobic respiration. But there are many endosymbiotic relationships in nature which are just as interdependent. For example, no termite could survive without the population of endosymbionts that lives inside its guts, digesting its woody diet for it. And the protists and bacteria that make up that population can't survive outside the termite. Complete interdependency. Now, the termite and its passengers look a lot more like independent creatures to us than a cell and its mitochondria. But they are actually no more independent of each other. So if we decide that the mitochondrion is just a part of the cell, then don't we have to also decide that the endosymbionts inside the termite's guts are just parts of the termite? If not, how do we justify insisting that there's a difference? Before you get too frustrated trying to sort this out, allow me to relieve your mind. There is, in fact, no answer to this question. Just the reinforcement of a very important lesson. Despite our human need to sort our world into neat, clean categories, the real universe often doesn't cooperate, and this is just such a case. We want to be able to decide "two separate organisms" or "parts of the same organism" in cases like this, but reality shows us that there are many situations which fall somewhere between these two categories. This is a lesson we learned when we examined the "alive" vs "not alive" issue, and again when we tried to decide how to functionally describe species. We want neat categories; nature doesn't cooperate.
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The main difference between prokaryotic and eukaryotic cells is that prokaryotic cellsdo not have a nucleus or membrane-bound organelles. Eukaryotes have both of these features.
Both prokaryotic and eukaryotic cells have DNA.
Flagella exist both in prokaryotic and eukaryotic cells. They are more prevalent, however in prokaryotic cells because they are single-celled organisms and depend on it for movement.
Both eukaryotic and prokaryotic cells have cell membranes.
Chloroplasts are only found in plant cells (eukaryotic).
Prokaryotic cells and eukaryotic cells have ribosomes
Mitochondria are found in most eukaryotic cells.
Cell walls can be found in plants (eukaryotic) as well as many prokaryotic cells.
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All cells fall into one of the two major classifications: prokaryotes or eukaryotes.
Prokaryotic Cells
Prokaryotes are evolutionarily ancient. They were here first and for billions of years were the only form of life. And even with the evolution of more complex eukaryotic cells, prokaryotes are supremely successful. All bacteria and bacteria-like Archaea are prokaryotic organisms.
Eukaryotic Cells
Eukaryotic cells are more complex, evolving from a prokaryote-like predecessor. Most of the living things that we are typically familiar with are composed of eukaryotic cells; animals, plants, fungi and protists. Eukaryotic organisms can either be single-celled or multi-celled.
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Prokaryotic cells lack a nucleus and membrane-bound organelles, which are present in eukaryotic cells. Bacteria and archaebacteria are prokaryotes, and plants, animals, and some single-celled organisms are eukaryotic. Prokaryotic cells do not have chromosomes, unlike eukaryotic cells.
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