Prokaryotes: structure and features of vital functions

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.

Peculiarities of the structure of prokaryotic cells

Prokaryotes are all living organisms whose cells do not contain a nucleus. Of the representatives of the five modern realms of living nature, 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 of a nucleus in their cells, they contain the genetic material. 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.

The structure of prokaryotes and eukaryotes

The peculiarities 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 its basis is cellulose, and in mushrooms - chitin.

History of the discovery

The peculiarities of the structure and vital activity of prokaryotes 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. Chatton in 1937 proposed to unite the 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.

Features of the surface apparatus

The surface apparatus of prokaryotes consists of a membrane and a 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 closely adhered to 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 representatives of prokaryotes have a mucous capsule outside. It protects organisms from drying out, mechanical damage, creates an additional osmotic barrier.

Prokaryotic organelles

The structure of the prokaryotic cell and eukaryotic cells has its significant differences, which primarily consist in 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 the 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.

What is a nucleoid

But the most significant difference is in the structure of the prokaryotic and eukaryotic gene. Hereditary information is possessed by all these organisms. In eukaryotes, it is located inside the decorated nucleus. This double-membrane organelle has its own matrix, which is called nucleoplasm, envelope and chromatin. It is not only the storage of genetic information, but also the synthesis of RNA molecules. In the nucleolus of them, subunits of ribosomes - 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 molecules of RNA and protein. 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.

Features of life activity

Prokaryotes, whose structure is not difficult, carry out rather complex processes of vital activity. This food, breathing, reproduction of their own kind, movement, metabolism ... And all this is possible only one microscopic cell, the dimensions of which range from 250 microns! So you can only talk about primitiveness relatively.

Features of the structure of prokaryotes determine the mechanisms 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, and ATP molecules are directly formed. Therefore, in fact, this is a real photophosphorylation.

Type of food

Bacteria and archaea are prokaryotes, the structure of which allows them to carry out different ways of feeding. Some of them are autotrophs. These organisms themselves synthesize organic substances 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.

Forms of reproduction

Prokaryotes, whose structure is represented by a single cell, 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 occurs. Some bacteria are also capable of forming cells of asexual reproduction - a spore.

Bacteria and Archaea: distinctive features

For a long time, the archaea, along with the bacteria, were representatives of the Kingdom of Drobyanka. 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 they eat, most of them are hemotrophs. And the substances that are split in the process of obtaining the energy of the Archaean are more diverse. This and 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 archaea. Most often in the nature there are commensals and mutualists. In the first case, the archaea feed on the substances of the host organism, 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 of animals, 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 archaeos were referred to the group of extremophiles, because they are able to inhabit both hot springs and in water bodies with increased salinity, and at depths with considerable pressure.

The meaning of prokaryotes in nature and human life

The role of prokaryotes in nature is considerable. First of all, they are the first living organisms that arose on the planet. Scientists have established that bacteria and archeas 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 in biotechnology with the aim 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 humans 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, the cells of which are devoid of a formal nucleus. Their genetic material is represented by a nucleoid consisting of a circular DNA molecule. Among modern organisms, prokaryotes include bacteria and archaea.