Biology: cells. Structure, function, functions

Cell biology is generally known to each of the school's curriculum. We suggest you to remember what you learned once, and also to discover something new about it. The name "cage" was proposed back in 1665 by the Englishman R. Hooke. However, it was not until the 19th century that it began to be studied systematically. Scientists are interested, among other things, and the role of cells in the body. They can be in a variety of different organs and organisms (eggs, bacteria, nerves, erythrocytes) or be independent organisms (protozoa). Despite all their diversity, many similarities are found in their functions and structure.

Cell functions

All of them are different in form and often in function. Can differ quite strongly and cells of tissues and organs of one organism. However, the biology of the cell distinguishes functions that are inherent in all of their varieties. It is here that protein synthesis always takes place. This process is controlled by a genetic apparatus. A cell that does not synthesize proteins is essentially dead. A living cell is one whose components are constantly changing. However, the main classes of substances remain unchanged.

All processes in the cell are carried out using energy. This food, breathing, reproduction, metabolism. Therefore, a living cell is characterized by the fact that energy metabolism is constantly taking place in it. Each of them has a common most important property - the ability to store energy and spend it. Among other functions, division and irritability can be noted.

All living cells can react to chemical or physical changes in the environment surrounding them. This property is called excitability or irritability. In cells, when excited, the rate of decomposition of substances and biosynthesis, temperature, oxygen consumption changes. In this state they perform the functions peculiar to them.

Cell structure

Its structure is rather complicated, although it is considered the simplest form of life in science such as biology. The cells are located in the intercellular substance. It provides them with breath, food and mechanical strength. The nucleus and cytoplasm are the main components of each cell. Each of them is covered with a membrane, the building element for which is a molecule. Biology has established that the membrane consists of a multitude of molecules. They are arranged in several layers. Due to the membrane, substances penetrate selectively. In the cytoplasm are organoids - the smallest structures. These are endoplasmic reticulum, mitochondria, ribosomes, cell center, Golgi complex, lysosomes. You will better understand how cells look, having studied the drawings presented in this article.

Membrane

When examining a plant cell in a microscope (for example, the root of a bow), one can notice that it is surrounded by a rather thick shell. The squid has a giant axon, the shell of which is of a completely different nature. However, it does not decide which substances should or should not be allowed into the axon. The function of the cell membrane is that it is an additional means of protecting the cell membrane. The membrane is called the "fortress wall of the cell." However, this is only true in the sense that it protects and protects its contents.

Both the membrane and the inner contents of each cell consist usually of the same atoms. We are talking about carbon, hydrogen, oxygen and nitrogen. These atoms are at the beginning of the periodic table. The membrane is a molecular sieve, very small (its thickness is 10 thousand times less than the thickness of the hair). Its pores resemble the narrow long passages made in the fortress wall of some medieval city. Their width and height are 10 times smaller than the length. In addition, the holes in this sieve are very rare. In some cells, the pores occupy only one millionth of the entire area of the membrane.

Core

Cell biology is also interesting from the point of view of the nucleus. This is the largest organelle, which first attracted the attention of scientists. In 1981, the cell nucleus was discovered by Robert Brown, a Scottish scientist. This organoid is a kind of cybernetic system, where the storage, processing, and then transfer to the cytoplasm of information, the volume of which is very large. The nucleus is very important in the process of heredity, in which it plays the main role. In addition, it performs the function of regeneration, that is, it can restore the integrity of the whole cell body. This organoid regulates all the most important cell functions. As for the shape of the nucleus, most often it is spherical, and also ovoid. Chromatin is the most important component of this organoid. It is a substance that is well colored by special nuclear paints.

A double membrane separates the nucleus from the cytoplasm. This membrane is associated with the Golgi complex and with the endoplasmic reticulum. On the nuclear membrane there are pores through which some substances easily pass, while others do it more difficult. Thus, its permeability is selective.

Nuclear juice is the inner core content. It fills the space between its structures. Nucleos (one or several) are necessarily present in the nucleus. They form ribosomes. There is a direct relationship between the size of the nucleoli and the activity of the cell: the nucleoli are the larger the more active the biosynthesis of the protein takes place ; And, on the contrary, in cells with limited synthesis they are either completely absent or small.

There are chromosomes in the nucleus. These are special threadlike formations. In addition to genital cells , there are 46 chromosomes in the nucleus of the cell of the human body. They contain information about hereditary predispositions of the organism, which is transmitted to the offspring.

Cells usually have one nucleus, but there are also multi-nuclear cells (in muscles, in the liver, etc.). If you remove the nucleus, the remaining parts of the cell become unviable.

Cytoplasm

The cytoplasm is a colorless mucous semisolid mass. It contains about 75-85% of water, about 10-12% of amino acids and proteins, 4-6% of carbohydrates, 2 to 3% of lipids and fats, and 1% of inorganic and some other substances.

The content of the cell in the cytoplasm is able to move. Due to this, organelles are placed optimally, and biochemical reactions proceed better, as is the process of separation of metabolic products. Different formations are represented in the cytoplasm layer: superficial outgrowths, flagella, cilia. The cytoplasm is permeated by a reticular system (vacuolar) consisting of flattened sacs, vesicles, tubules communicating with each other. They are associated with the outer plasma membrane.

Endoplasmic reticulum

This organoid was named so because it is located in the central part of the cytoplasm (from the Greek language the word "endon" is translated as "inside"). EPS - a very branched system of bubbles, tubules, tubules of various shapes and sizes. They are delimited from the cytoplasm of the cell by membranes.

There are two types of EPS. The first is granular, which consists of cisterns and tubules, the surface of which is strewn with granules (granules). The second type of EPS is agranular, that is, smooth. The edges are ribosomes. It is curious that basically granular EPS is observed in the cells of the embryos of animals, whereas in adult forms it is usually agranular. As is known, ribosomes are the site of protein synthesis in the cytoplasm. Proceeding from this, it can be assumed that granular EPS is mainly in cells where active protein synthesis occurs. The agranular network is believed to be represented mainly in those cells where active lipid synthesis takes place, that is, fats and various fat-like substances.

Both types of EPS do not just take part in the synthesis of organic substances. Here, these substances accumulate, as well as transported to the necessary places. EPS also regulates the metabolism that occurs between the environment and the cell.

Ribosomes

These are cellular non-membrane organelles. They consist of protein and ribonucleic acid. These parts of the cell are still not fully understood from the point of view of the internal structure. In an electron microscope, the ribosomes look like mushroom-like or rounded granules. Each of them is divided into a small and a large part (subunits) by means of a groove. Several ribosomes are often combined with a strand of a special RNA (ribonucleic acid), called i-RNA (information). Due to these organoids, protein molecules are synthesized from amino acids.

Golgi Complex

Products of biosynthesis enter the lumens of tubules and cavities of EPS. Here they are concentrated in a special apparatus called the Golgi complex (in the figure above it is designated as golgi complex). This device is near the nucleus. He takes part in the transfer of biosynthetic products, which are delivered to the surface of the cell. Also, the Golgi complex participates in their removal from the cell, in the formation of lysosomes, etc.

This organoid was discovered by Camilio Golgi, an Italian cytologist (years of life - 1844-1926). In honor of him in 1898 he was called the Golgi apparatus (complex). The proteins produced in the ribosomes enter this organelle. When they are needed by some other organelle, part of the Golgi apparatus is separated. Thus, the protein is transported to the desired location.

Lysosomes

Telling about the appearance of cells and what organelles are included in their composition, it is necessary to mention also about lysosomes. They have an oval shape, they are surrounded by a single-layer membrane. In lysosomes, there is a set of enzymes that destroy proteins, lipids, carbohydrates. If the lysosomal membrane is damaged, the enzymes break down and destroy the contents inside the cell. As a result, she dies.

Cellular Center

It is found in cells that are able to divide. The cell center consists of two centrioles (rod-shaped corpuscles). Being near the Golgi complex and the nucleus, it participates in the formation of the division spindle, in the process of cell division.

Mitochondria

Energy organoids include mitochondria (pictured above) and chloroplasts. Mitochondria are the unique energy stations of each cell. It is in them that energy is extracted from nutrients. Mitochondria have a variable form, but most often they are granules or filaments. The number and size of them are unstable. It depends on what is the functional activity of a cell.

If you consider an electronic micrograph, you can see that the mitochondria have two membranes: the inner and the outer. The inner forms outgrowths (cristae), lined with enzymes. Due to the presence of crista, the total surface of the mitochondria increases. This is important for the activity of enzymes to be active.

In mitochondria, scientists discovered specific ribosomes and DNA. This allows these organoids to multiply independently in the process of cell division.

Chloroplasts

As for chloroplasts, in form it is a disk or a ball having a double shell (inner and outer). Inside this organoid there are also ribosomes, DNA and granules - special membrane formations, connected both with the inner membrane and with each other. Chlorophyll is located in the membranes of the gran. Thanks to it, the energy of sunlight turns into chemical energy adenosine triphosphate (ATP). In chloroplasts, it is used to synthesize carbohydrates (formed from water and carbon dioxide).

Agree, the information above should be known not only to pass a biology test. A cage is the building material that our body is made of. And all living nature is a complex set of cells. As you can see, there are many components in them. At first glance it may seem that studying the structure of the cell is not an easy task. However, if you understand, this topic is not so complicated. It is necessary to know it in order to understand well such a science as biology. The composition of the cell is one of its fundamental themes.