Prokaryotes are ... Prokaryotes and Eukaryotes
From the moment the Earth became a full-fledged planet, life gradually began to emerge on it. First of all, cells appeared - a building material for all living things. The diversity of life forms now observed is not only pleasing to the eye, but also makes us think about the complexity of the evolutionary processes. Despite the dissimilarity of organisms, the cells of which they are composed resemble each other. But scientists nevertheless found differences and divided them into two large groups: prokaryotes and eukaryotes. At the same time, viruses are classified separately, and science cannot yet determine whether these are living organisms.
Microworld among us
Now people live in the big world, knowing that a small universe is nearby, teeming with various microorganisms: some of them are loyal to humans, others are dangerous.It is about the diversity of bacterial life. Bacteria belong to prokaryotes. Whereas more complex eukaryotes are schematically divided into several kingdoms: plants, animals, fungi and slizheviki.
Bacteria (prokaryotes) have the following characteristics:
- single, nuclear-free cell (nucleoid formation);
- binary division;
- difference of forms, sizes;
- the presence or absence of organelles.
Bacteria-prokaryotes are divided into convoluted (vibrios), rod-shaped (bacilli), similar to a corkscrew (spirilla) and spherical (cocci). The cells are moved either with the help of mucus or using flagella.
It has been proven that prokaryotes appeared first. If you translate a word from the Greek language, then "prokaryotes" are cells in which there is no nucleus.
But in such a categorical definition it is necessary to make some amendments. Prokaryotes contain nucleus-like structures that do not have membranes that are in the cytoplasmic fluid. Such unformed nuclei are called nucleoids. It is in them that the modest amount of genetic information of the cell is located.
The simplest cells appeared about 35 million centuries ago. Following this fantastic figure, it can be argued that prokaryotes are the first living matter on the then young Earth.
More. More voluminous. More difficult
Turning to the knowledge of the ancient Greeks, one can find out that "eukaryotes" means "possessing a nucleus", and this statement is completely untrue.
Such cells, in modern terms, are more advanced.The presence of a full core plays an important role in this. A fully formed core with two layers of the membrane reliably protects the genetic code contained in it. Partially, DNA molecules are located outside the nucleus, in chloroplasts and mitochondria. Among other things, eukaryotes are much more nuclear-free in size and volume.
Eukaryotes appeared about two billion years later, after the emergence of elementary prokaryotes. It can be said that they relate to prokaryotes, as if to the progenitors of truly nuclear.
Armed with a microscope
Prokaryotic cells are not only much smaller than eukaryotes, they differ significantly in their structural features.Prokaryotes and eukaryotes differ in unequal complexity of the structure, where the prokaryotic cell is much simpler.
- Mucous capsule. The function of the capsule comes down to protecting the cell: it protects against drying out and the action of antibodies. Consists mainly of polysaccharides, with polypeptide inclusions.
- The wall of the cell. Thanks to the murein, which this shell consists of, this structural component is distinguished by its rigidity. It performs a triple function: protective, transport, reliably fixes the shape and integrity of the cell.
- Cell ProtoplastDue to the difference in the growth of the protoplast and the outer cell membrane invaginations occur - internal deflections. Such processes allow the formation of organoids, called mesosomes. They perform the necessary cellular functions. While the ribosome is entrusted with the mission of protein synthesis.
- Nucleoid. An elongated, ellipsoidal structure that acts as a nucleus. It is not separated from the cytoplasm, so scientists do not classify it as a full-fledged nucleus. Extra DNA information may be carried by very small particles.–plasmids.
- Optional organelles. Presented by various patches: sulfur, polyphosphates, oils, glycogen, polysaccharide grains. Also organisms include flagella, which help the cell to move, and drank - protein inclusions that perform the function of attachment.
If we can talk about the simplicity of the structure applicable to such a complex living structure as a cell, then, of course, prokaryotes are simple structures.
The structure of a true nuclear
Eukaryotes, by contrast, have a complex structure. Arising, according to the assumptions of the academic world, on the basis of prokaryotes, they contain in their composition more perfect structures.
- Membrane. It performs a selective protective function.
- Cell wall, or glycolix (in animals). In mushrooms and plants, it plays a stabilizing and shape-retaining role. It consists of chitin and cellulose fibers, respectively. Animals do without a cell wall due to the action of other mechanisms.
- Cytoplasm. It consists of a solution of inorganic and organic substances under the general name hyaloplasm. The main component capable of carrying out chemical reactions is protein.
- Core. The most important component of the cell. It stores genetic information in chromosomes. The core is protected by two membranes.
- Organoids. Located on the territory of hyaloplasm and represented by a variety of names. The most important components: mitochondria, Golgi complex, chloroplasts, lysosomes, ribosomes.
The nucleus of eukaryotes can be divided in two ways: mitosis and meiosis. It is extremely important for the development and operation of the cell.
Differences between the two groups can be systematized and described in a language that is understandable to all. Especially since the cells of prokaryotes and eukaryotes obviously differ.comparison table
|Signs of||Prokaryotic cells||Eukaryotic cells|
|Chronological niche||3.5 billion||one and a half billion years|
|Magnitude||0.01 mm||0.1 mm (more than 1000 times)|
|Genome||is in the nucleoid, designed in the form of an ellipse||located in the nucleus containing chromosomes; partly DNA is located in mitochondria and chloroplasts|
|Organoids||sometimes found, but in small quantities and without membrane||in the set; plastids and mitochondria have their own genome and ability to reproduce; each organella has a well-defined function|
|Division method||binary (in half)||mitosis: division with chromosome preservation; meiosis: a twofold reduction in the number of chromosomes|
sometimes mucus helps to move, more often - protein threads
|using flagella (complex, layered processes) and cilia|
|The phenomenon of phagocytosis||absent||presumably appeared to ensure the vital activity of a large cell; thanks to this phenomenon appeared predators|
Features of prokaryotes
After the electron microscope appeared, it became possible to differentiate eukaryotes and prokaryotes, and also to study them in more detail.
The main difference between pre-nuclear cells is that prokaryotes are bacteria that are present everywhere: in the human body, in the water, in the air, in plants.A lot of bacteria are in the soil. They even live in nuclear reactors!
Despite their small size, prokaryotes are the custodians of coded genetic information that affects the vital activity of organisms. For example, in plasmids that are free-floating among the waters of a cytoplasmic cocktail, a gene may be found that affects the resistance of the bacterium to drugs.
In addition, the simplicity of the organization does not prevent bacteria from flourishing, actively proliferating, along with more complex eukaryotes.
Dilemma: good or harm
The value of eukaryotes is not subject to doubt: thanks to them, various forms of life have appeared. But with bacteria is not so simple. On the one hand, thanks to microorganisms in the intestine, people can successfully digest food, synthesize and absorb vitamins. Also, prokaryotes covering the skin or mucous membranes of a person perform a protective function.
Some bacteria are necessary for the production of cheese, sour cream, sauerkraut. Interestingly, bacteria have been isolated that have an effect similar to antibiotics.
On the other hand, certain types of nuclear-free can cause illness or spoil products.They are able not only to release toxins, but also to destroy the cells of an occupied organism.
Therefore, it is certainly impossible to talk about the benefits or harms of prokaryotes: it all depends on their types. But in any case, these smallest cells, humanity owes its existence.