Biology of the cell in general terms is known to everyone from the school curriculum. We invite you to remember what you once studied, as well as discover something new about it. The name "cell" was proposed as early as 1665 by the Englishman R. Hooke. However, it was only in the 19th century that it began to be studied systematically. Scientists were interested, among other things, in the role of the cell in the body. They can be part of many different organs and organisms (eggs, bacteria, nerves, erythrocytes) or be independent organisms (protozoa). Despite all their diversity, there is much in common in their functions and structure.
Cell functions
They are all different in form and often in function. Cells of tissues and organs of one organism can also differ quite strongly. However, the biology of the cell highlights the functions that are inherent in all their varieties. This is where protein synthesis always takes place. This process is controlled by the genetic apparatus. A cell that does not synthesize proteins is essentially dead. A living cell is one whose components change all the time. However, the main classes of substances remainunchanged.
All processes in the cell are carried out using energy. These are nutrition, respiration, reproduction, metabolism. Therefore, a living cell is characterized by the fact that energy exchange takes place in it all the time. Each of them has a common most important property - the ability to store energy and spend it. Other functions include division and irritability.
All living cells can respond to chemical or physical changes in their environment. This property is called excitability or irritability. In cells, when excited, the rate of decay of substances and biosynthesis, temperature, and oxygen consumption change. In this state, they perform the functions peculiar to them.
Cell structure
Its structure is quite complex, although it is considered the simplest form of life in such a science as biology. Cells are located in the intercellular substance. It provides them with breathing, nutrition and mechanical strength. The nucleus and cytoplasm are the main components of every cell. Each of them is covered with a membrane, the building element for which is a molecule. Biology has established that the membrane is made up of many molecules. They are arranged in several layers. Thanks to the membrane, substances penetrate selectively. In the cytoplasm are organelles - the smallest structures. These are the endoplasmic reticulum, mitochondria, ribosomes, cell center, Golgi complex, lysosomes. You will get a better idea of what cells look like by studying the pictures presented in this article.
Membrane
When examining a plant cell under a microscope (for example, an onion root), you can see that it is surrounded by a rather thick shell. The squid has a giant axon, the sheath 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 "stronghold of the cell". However, this is only true in the sense that it protects and shields its contents.
Both the membrane and the internal contents of each cell usually consist of the same atoms. These are carbon, hydrogen, oxygen and nitrogen. These atoms are at the beginning of the periodic table. The membrane is a molecular sieve, very fine (its thickness is 10 thousand times less than the thickness of a hair). Its pores resemble narrow long passages made in the fortress wall of some medieval city. Their width and height are 10 times less than their length. In addition, holes in this sieve are very rare. In some cells, the pores occupy only one millionth of the entire membrane area.
Core
Cell biology is also interesting from the point of view of the nucleus. This is the largest organoid, the first to attract 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 information is stored, processed, and then transferred to the cytoplasm, the volume of which is very large. The core is very important in the processheredity, in which it plays a major role. In addition, it performs the function of regeneration, that is, it is able to restore the integrity of the entire cellular body. This organoid regulates all the most important functions of the cell. As for the shape of the nucleus, most often it is spherical, as well as ovoid. Chromatin is the most important component of this organelle. This is a substance that stains well with special nuclear dyes.
A double membrane separates the nucleus from the cytoplasm. This membrane is associated with the Golgi complex and with the endoplasmic reticulum. The nuclear membrane has pores through which some substances easily pass, while others are more difficult to do so. Thus, its permeability is selective.
Nuclear juice is the inner content of the kernel. It fills the space between its structures. Necessarily in the nucleus there are nucleoli (one or more). They form ribosomes. There is a direct relationship between the size of the nucleoli and the activity of the cell: the larger the nucleoli, the more actively protein biosynthesis occurs; and, conversely, in cells with limited synthesis, they are either completely absent or small.
Chromosomes are in the nucleus. These are special filamentous formations. In addition to the sex chromosomes, there are 46 chromosomes in the nucleus of a cell in the human body. They contain information about the hereditary inclinations of the body, which is transmitted to offspring.
Cells usually have one nucleus, but there are also multinucleated cells (in muscles, liver, etc.). If the nuclei are removed, the remaining parts of the cell will become unviable.
Cytoplasm
Cytoplasm is a colorless mucous semi-liquid mass. It contains about 75-85% water, approximately 10-12% amino acids and proteins, 4-6% carbohydrates, 2 to 3% lipids and fats, as well as 1% inorganic and some other substances.
The content of the cell, located in the cytoplasm, is able to move. Due to this, the organelles are placed optimally, and biochemical reactions proceed better, as well as the process of excretion of metabolic products. Different formations are presented in the cytoplasm layer: superficial outgrowths, flagella, cilia. The cytoplasm is permeated by a mesh system (vacuolar), consisting of flattened sacs, vesicles, tubules that communicate with each other. They are connected to the outer plasma membrane.
Endoplasmic reticulum
This organelle was named so because it is located in the central part of the cytoplasm (from Greek, the word "endon" is translated as "inside"). EPS is a very branched system of vesicles, tubules, tubules of various shapes and sizes. They are separated from the cytoplasm of the cell by membranes.
There are two types of EPS. The first is granular, which consists of tanks and tubules, the surface of which is dotted with granules (grains). The second type of EPS is agranular, that is, smooth. Grans are ribosomes. Curiously, granular EPS is mainly observed in the cells of animal embryos, while in adult forms it is usually agranular. Ribosomes are known to be the site of protein synthesis in the cytoplasm. Based on this, it can be assumed that granular EPS occurs mainly in cells where active protein synthesis occurs. The agranular network is believed to be represented mainly in those cells where active synthesis of lipids occurs, that is, fats and various fat-like substances.
Both types of EPS are not just involved in the synthesis of organic substances. Here these substances accumulate and are also transported to the necessary places. EPS also regulates the metabolism that occurs between the environment and the cell.
Ribosome
These are cellular non-membrane organelles. They are made up of protein and ribonucleic acid. These parts of the cell are still not fully understood in terms of internal structure. In an electron microscope, ribosomes look like mushroom-shaped or rounded granules. Each of them is divided into small and large parts (subunits) using a groove. Several ribosomes are often joined together by a special RNA (ribonucleic acid) strand called i-RNA (messenger). Thanks to these organelles, protein molecules are synthesized from amino acids.
Golgi complex
Products of biosynthesis enter the lumen of the tubules and cavities of the EPS. Here they are concentrated into a special apparatus called the Golgi complex (indicated as the golgi complex in the figure above). This apparatus is located near the nucleus. It takes part in the transfer of biosynthetic products that are delivered to the cell surface. Also, the Golgi complex is involved in their removal from the cell, in the formationlysosomes, etc.
This organelle was discovered by Camilio Golgi, an Italian cytologist (life - 1844-1926). In honor of him, in 1898, he was named the apparatus (complex) of the Golgi. Proteins produced in ribosomes enter this organelle. When some other organoid needs them, part of the Golgi apparatus is separated. Thus, the protein is transported to the required place.
Lysosomes
Telling about how cells look and what organelles are included in their composition, it is necessary to mention lysosomes. They have an oval shape, they are surrounded by a single-layer membrane. Lysosomes contain a set of enzymes that break down proteins, lipids, and carbohydrates. If the lysosomal membrane is damaged, enzymes break down and destroy the contents inside the cell. As a result, she dies.
Cell center
It is found in cells that are capable of dividing. The cell center consists of two centrioles (rod-shaped bodies). 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 organelles include mitochondria (pictured above) and chloroplasts. Mitochondria are the original powerhouses of every cell. It is in them that energy is extracted from nutrients. Mitochondria have a variable shape, but most often they are granules or filaments. Their number and size are not constant. It depends on what is the functional activity of a particular cell.
If we consider an electron micrograph,It can be seen that mitochondria have two membranes: inner and outer. The inner one forms outgrowths (cristae) covered with enzymes. Due to the presence of cristae, the total surface of mitochondria increases. This is important for the activity of enzymes to proceed actively.
In mitochondria, scientists have discovered specific ribosomes and DNA. This allows these organelles to reproduce on their own during cell division.
Chloroplasts
As for chloroplasts, it is a disc or a ball in shape, having a double shell (inner and outer). Inside this organoid there are also ribosomes, DNA and grana - special membrane formations associated both with the inner membrane and with each other. Chlorophyll is found in the membranes of the gran. Thanks to him, the energy of sunlight is converted into the chemical energy of adenosine triphosphate (ATP). In chloroplasts, it is used to synthesize carbohydrates (formed from water and carbon dioxide).
Agree, the information presented above is necessary to know not only in order to pass a biology test. The cell is the building material that makes up our body. And all living nature is a complex set of cells. As you can see, they have many components. At first glance, it may seem that studying the structure of a cell is not an easy task. However, if you look, this topic is not so complicated. It is necessary to know it in order to be well versed in a science such as biology. The composition of the cell is one of its fundamental themes.
