In this article we will consider the structure of prokaryotes and eukaryotes. These organisms significantly differ in the level of organization. And the reason for this is the peculiarities of the structure of genetic information.
Prokaryotes are all living organisms, cellswhich do not contain a kernel. Of the representatives of the five modern realms of wildlife, only one thing belongs to them - Bacteria. Prokaryotes, the structure of which we are considering, also include representatives of blue-green algae and archaea.
Despite the absence in their cells issuednucleus, the genetic material they contain. This allows you to store and transmit hereditary information, but limits the variety of ways to multiply. Reproduction of all prokaryotes occurs by dividing their cells in two. They are not capable of mitosis and meiosis.
Features of the structure of prokaryotes and eukaryotes,which distinguish them, are quite significant. In addition to the structure of genetic material, this also applies to many organelles. Eukaryotes, which include plants, fungi and animals, contain mitochondria in the cytoplasm, the Golgi complex, the endoplasmic reticulum, and many plastids. In prokaryotes they are absent. The cell wall, which is present in both of them, differs in chemical composition. The bacteria in its composition include complex carbohydrates pectin or murine, while in plants it is based on cellulose, and in mushrooms - chitin.
Features of structure and vital functionsProkaryotes became known to scientists only in the 17th century. And this despite the fact that these creatures existed on the planet since its inception. In 1676, they were first considered in the optical microscope by its creator, Anthony van Leeuwenhoek. Like all microscopic organisms, the scientist called them "animalikulami." The term "bacteria" appeared only at the beginning of the 19th century. It was suggested by the famous German naturalist Christian Ehrenberg. The concept of "prokaryotes" arose later, in the era of the creation of an electron microscope. And first, scientists have established the fact of the difference in the structure of the genetic apparatus of cells of different creatures. E. Chatteron in 1937 proposed to unite on this basis organisms into two groups: pro- and eukaryotes. This division exists to this day. In the second half of the 20th century, a distinction was discovered among the prokaryotes themselves: archeas and bacteria.
Surface apparatus of prokaryotes consists ofmembrane and cell wall. Each of these parts has its own characteristics. Their membrane is formed by a double layer of lipids and proteins. Prokaryotes, whose structure is quite primitive, have two types of cell wall structure. Thus, in gram-positive bacteria, it consists mainly of peptidoglycan, has a thickness of up to 80 nm and is snug against the membrane. A characteristic feature of this structure is the presence of pores through which a number of molecules penetrate. The cell wall of gram-negative bacteria is very thin - a maximum of 3 nm. It is not snug against the membrane. Some prokaryotes have a mucous capsule outside. It protects organisms from drying out, mechanical damage, creates an additional osmotic barrier.
The structure of prokaryotes and eukaryotes has its ownEssential differences, which are primarily the presence of certain organelles. These permanent structures determine the level of development of organisms in general. In prokaryotes, most of them are absent. Synthesis of protein in these cells occurs ribosomes. The water prokaryotes contain aerosomes. These are gas cavities that provide buoyancy and regulate the degree of immersion of organisms. Only in cells of prokaryotes are mesosomes. These folds of the cytoplasmic membrane occur only during the use of chemical fixation methods during preparation of prokaryotic cells to microscopy. The organelles of the movement of bacteria and archaea are cilia or flagella. And attachment to the substrate is performed by saws. These structures, formed by protein cylinders, are also called villi and pili.
But the most significant difference is the structure of the geneprokaryotes and eukaryotes. Hereditary information is possessed by all these organisms. In eukaryotes, it is located inside a decorated nucleus. This double-membrane organelle has its own matrix, which is called nucleoplasm, membrane and chromatin. It is not only the storage of genetic information, but also the synthesis of RNA molecules. In the nucleoli of these, the subunits of the ribosomes, the organelles responsible for protein synthesis, are subsequently formed.
The structure of prokaryotic genes is simpler. Their hereditary material is represented by a nucleoid or nuclear region. DNA in prokaryotes is not packed into chromosomes, but has an annular closed structure. The nucleoid also includes RNA and protein molecules. The latter are similar in function to the histones of eukaryotes. They are involved in doubling DNA, synthesizing RNA, restoring the chemical structure and rupturing of nucleic acids.
Prokaryotes, the structure of which does not differcomplexity, carry out quite complex processes of life. This food, breathing, reproduction of their own kind, movement, metabolism ... And all this is capable of only one microscopic cell, the dimensions of which range from 250 microns! So it is possible to speak about primitiveness only relatively.
Features of the structure of prokaryotes determine andmechanisms of their physiology. For example, they are able to receive energy in three ways. The first is fermentation. It is carried out by some bacteria. This process is based on oxidation-reduction reactions, during which ATP molecules are synthesized. It is a chemical compound, the splitting of which releases energy in several stages. Therefore, it is not in vain called a "cellular battery". The next way is breathing. The essence of this process is the oxidation of organic substances. Some prokaryotes are capable of photosynthesis. Their examples are blue-green algae and purple bacteria, which contain plastids in cells. But the archaea are capable of chlorophilic photosynthesis. During this process, carbon dioxide is not fixed, but ATP molecules are formed directly. Therefore, in fact, this is a real photophosphorylation.
Bacteria and archaea are prokaryotes, a structurewhich allows them to implement and different ways of feeding. Some of them are autotrophs. These organisms synthesize organic substances themselves during photosynthesis. In the cells of such prokaryotes there is chlorophyll. Some bacteria get energy by splitting some organic compounds. Their type of food is called hemotropic. Representatives of this group are iron - and sulfur bacteria. Others absorb only ready-made compounds. They are called heterotrophs. Most of them lead a parasitic way of life and live only inside the cells of other beings. A variation of this group are saprotrophs. They feed on products of vital activity or decomposing organic substances. As you can see, the ways of eating prokaryotes are quite diverse. This fact and contributed to their wide distribution in all habitats.
Prokaryotes, whose structure is represented by onecell, multiply by dividing it into two parts or by budding. This feature is also due to the structure of their genetic apparatus. The process of binary division is preceded by a doubling, or DNA replication. In this case, the nucleic acid molecule is first untwisted, after which each strand is duplicated according to the principle of complementarity. The resulting chromosomes diverge to the poles. Cells increase in size, between them a constriction is formed and then their final isolation takes place. Some bacteria are also capable of forming cells of asexual reproduction - a spore.
For a long time, the archaea along with the bacteria wererepresentatives of the Kingdom of Droboyanka. And indeed, they have many similar features of the structure. This is primarily the size and shape of their cells. However, biochemical studies have shown that they have a number of similarities with eukaryotes. This is the nature of enzymes, under the influence of which the processes of synthesis of RNA and protein molecules occur.
By the way of feeding, most of them arehemotrophs. And the substances that are split in the process of obtaining the energy of the Archaean are more diverse. This complex carbohydrates, and ammonia, and metal compounds. There are among the archaea and autotrophs. Very often they enter into a symbiotic relationship. There are no parasites among the archaeas. Most often in the nature there are commensals and mutualists. In the first case, the archaea feed on the host substances, but do not do any harm to it. Unlike this kind of symbiosis, with mutualistic relationships, both organisms benefit. Some of them are metagenes. Such archaeans live in the digestive system of humans and ruminant mammals, causing excessive formation of gases in the intestine. These organisms multiply by binary division, budding or by fragmentation.
Archeans have mastered almost all habitats. They are especially diverse in the composition of plankton. Initially, all the archaeos were referred to the group of extremophiles, since they are able to inhabit both hot springs and in water bodies with increased salinity, and at depths with considerable pressure.
The role of prokaryotes in nature is significant. First of all, they are the first living organisms that arose on the planet. Scientists have established that bacteria and archeans arose about 3.5 billion years ago. The theory of symbiogenesis suggests that some organelles of eukaryotic cells also originated from them. In particular, we are talking about plastids and mitochondria.
Many prokaryotes find their application inbiotechnology for the purpose of obtaining medicines, antibiotics, enzymes, hormones, fertilizers, herbicides. Man has long used the useful properties of lactic acid bacteria for making cheese, kefir, yoghurt, sauerkraut products. With the help of these organisms, water bodies and soils are purified, and ores of various metals are enriched. Bacteria form the microflora of the intestine of man and many animals. Along with the Archean they circulate many substances: nitrogen, iron, sulfur, hydrogen.
On the other hand, many bacteria are the causative agent of dangerous diseases, regulating the number of many species of plants and animals. These include plague, syphilis, cholera, anthrax, diphtheria.
So, prokaryotes are called organisms, cellswhich are deprived of a decorated core. Their genetic material is represented by a nucleoid consisting of a circular DNA molecule. Among modern organisms, prokaryotes include bacteria and archaea.
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