Organisms of living nature mainly have cellular structure. In this article we will tell you in more detail about the structural features and functioning of cells, and introduce them to their chemical composition and varieties.
Structural features
The cell is the unit of structure and vital activity of all living things on our planet. They can have different sizes (from 3 to 100 microns) and shapes (cylindrical, spherical, oval), perform various functions, and participate in all kinds of metabolic processes.
From common features chemical composition and structure can be identified.
The main elements of the chemical composition are carbon, oxygen, nitrogen and hydrogen. These macroelements make up the bulk of all components. Among not organic matter Of particular importance are water and mineral salts, which are presented in the form of ions. These include iron, iodine, potassium, calcium, phosphorus, chlorine, etc.
Rice. 1. Chemical composition.
Also constituent elements are organic substances: carbohydrates, proteins, nucleic acids, lipids. The following table will help you understand the functions of each of them:
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The structural elements of a cell are the cell membrane, nucleus and cytoplasm with organelles. Each of the constituent elements has its own characteristics and functions. For example:
- core contains the genetic code and regulates all processes occurring within the cellular organism;
- cell membrane protects from environmental influences, gives shape;
The cell membrane of plants is much denser than that of animals. This is possible due to the presence of cellulose in the composition.
- cytoplasm ensures the interconnection of all organelles within the cell.
Among the organelles in all cells one can find ribosomes, lysosomes, the Golgi apparatus, mitochondria, and the endoplasmic reticulum.
Rice. 2. Cell structure.
Plant and animal cells are different from each other. Thus, a plant organism has vacuoles and plastids, which animals do not have. And the animal body contains cell centrioles, which are involved in division processes.
Features of life
The main manifestations of cell life are metabolic processes and energy conversion.
The formation of organic substances, which is accompanied by energy consumption, is called assimilation.
The breakdown or breakdown of organic substances, which releases energy, is called dissimilation.
Rice. 3. Cell activity
The sun is the main source of energy on Earth. Plants under the influence sun rays produce ATP molecules. Adenosine triphosphate (ATP) is an organic substance that acts as a kind of battery in living organisms.
Photosynthesis, which occurs in plant cells, gives oxygen to the atmosphere. Thanks to it, breathing is possible, and therefore the existence of all life on the planet.
Inside plants, under the influence of the Sun, organic substances are formed, which are consumed by other species of living nature (fungi, animals, bacteria).
Thanks to plants, all living organisms are provided not only with oxygen, but also with nutrients.
What have we learned?
The cell, like all living organisms, has its own characteristics in structure and life. Every cellular organism has a shell, nucleus and cytoplasm with organelles. The chemical composition of all cells is the same. The main components are carbon, oxygen, hydrogen and nitrogen. The main manifestations of cell life are the processes of assimilation and dissimilation.
Test on the topic
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A cell is an elementary living system, the basis of the structure and vital activity of all living organisms. It is known that they are unicellular (for example, various, as well as protozoa) or multicellular. The names themselves indicate that the structure of these organisms is based on structural unit- cell.
Living matter is divided into two superkingdoms - and (in Lately some are divided into two superkingdoms - true and archaebacteria). Cyanobacteria are also prokaryotic organisms; all other organisms, from unicellular protozoa to multicellular plants and animals, are eukaryotic.
The cells of organisms of these superkingdoms have common basic properties: they have similar basic systems, systems for transmitting genetic information (replication according to the matrix principle), energy supply, etc. But there are many differences between them. Firstly, in prokaryotic cells, the DNA molecules that determine the hereditary properties of organisms are not assembled in the cellular form characteristic of eukaryotic cells. Secondly, prokaryotic cells do not have many of the special structures inside the cells, the so-called organelles, characteristic of eukaryotic cells. Eukaryotic cells are more complexly organized; they can specialize within very wide limits and be part of multicellular organisms(see Cellular specialization (differentiation)).
In their structure and basic biochemical properties, different cells are very similar, which indicates the unity of their origin at the dawn of the living world (see).
What is a cell? A cell is a system consisting of complex organic molecules and also containing small organic and inorganic molecules. The main properties of this system are: self-reproduction, constant and energy with the external environment, its structural isolation from external environment.
All cells are separated both from their environment and from each other by a thin surface film - a membrane (plasma membrane). This membrane is built from lipoproteins and surrounds the contents of the cell, the cytoplasm and, on all sides. Plasma membrane has very important properties: it limits the free movement of substances from the cell to the outside and, conversely, selectively allows substances and molecules to pass through, thus maintaining the constancy of the composition and properties of the cytoplasm. In addition, special structures are located on the plasma membrane protein complexes(), which “recognize” substances, select them and, with the help of others (carriers), actively transport them in or out of the cell.
In the cytoplasm of cells there are special, complexly organized systems that perform various loads (functions). These are organelles.
The organelles of prokaryotic cells () include a nucleoid - a component containing DNA, a small number of membrane vesicles (for example, membrane vesicles carrying photosensitive - and some) and special movement organelles -
Basic concepts and terms on the topic: Organoids; cytolemma; hyaloplasm; metabolism; DNA; RNA; gene; heredity.
Topic study plan(list of questions required to study):
1. A cell is a unit of structure and vital activity of an organism.
2. Metabolism and energy conversion in the cell.
3. The DNA molecule is a carrier of hereditary information.
1 . All cells are characterized by the following manifestations of vital activity:
The main manifestations of cell activity
Plant and animal cells have overall plan buildings. Let's look at the main parts of the cell:
Components of a cell
Table 4. Cell structure and functions
| Plasma membrane | Isolates the cell from the external environment. Selectively permeable. | |
| Cell wall | Contains cellulose and is the “framework” of plants. | |
| EPS | ||
| Ribosomes | The organelle is round or mushroom-shaped. Consists of RNA and protein. | Protein synthesis |
| Mitochondria | It has a double-membrane structure. The inner membrane forms cristae (folds) on which there are many enzymes that ensure energy metabolism in the cell. | Is respiratory energy center cells. |
| Lysosomes | Single-membrane organelle of round shape. Formed on the Golgi Apparatus. | Carries out intracellular digestion of nutrients. Destroys the structures of the cell itself when they die and removes them from it. |
| Plastids | Chloroplasts - acquire green color, have their own DNA. | Provide the process of photosynthesis. |
| Leukoplasts – White color | Place where nutrients are deposited. | |
| Chromoplasts are colored. | Give the petals different colors. | |
| Pigment | Provides skin color. | |
| Vacuoles | The cavities are filled with cell sap. | In plants - contain nutrients and final products of metabolism. |
| Nuclear membrane | Protective function; Communication with the cytoplasm | |
| Chromatin substance | XX, XY | Forms genes and then chromosomes; There are 23 pairs or 46. |
Rice. 9. Cell structures
2. In living organisms, any process is accompanied by the transfer of energy. Energy is defined as the ability to do work. Metabolism and energy is a set of physical, chemical and physiological processes of transformation of substances and energy in living organisms, as well as the exchange of substances and energy between the body and the environment. Metabolism in living organisms consists of the intake of various substances from the external environment, their transformation and use in vital processes and the release of the resulting decomposition products into environment.
All transformations of matter and energy occurring in the body are combined common name - metabolism(metabolism).
Metabolism can be divided into two interrelated but multidirectional processes: anabolism (assimilation) and catabolism (dissimilation).
Anabolism is a set of processes of biosynthesis of organic substances (cell components and other structures of organs and tissues). It ensures growth, development, renewal of biological structures, as well as energy accumulation (synthesis of macroergs).
Catabolism is a set of processes of splitting complex molecules into simpler substances, using some of them as substrates for biosynthesis and splitting the other part into final metabolic products with the formation of energy. The end products include carbon (about 230 ml/min), carbon monoxide (0.007 ml/min), urea (about 30 g/day), and other substances.
3. Deoxyribonucleic acid (DNA) - a macromolecule that ensures storage, transmission from generation to generation and implementation of the genetic program for the development and functioning of living organisms. The main role of DNA in cells is the long-term storage of information about the structure of RNA and proteins.
In eukaryotic cells (for example, animals or plants), DNA is found in the cell nucleus as part of the chromosomes, as well as in some cellular organelles (mitochondria and plastids). In the cells of prokaryotic organisms (bacteria and archaea), a circular or linear DNA molecule, the so-called nucleotide, is attached from the inside to cell membrane. In prokaryotes and lower eukaryotes (for example, yeast), small autonomous, mostly circular DNA molecules called plasmids are also found. In addition, single- or double-stranded DNA molecules can form the genome of DNA viruses.
From a chemical point of view, DNA is a long polymer molecule consisting of repeating blocks - nucleotides. Each nucleotide consists of a nitrogenous base, a sugar (deoxyribose) and a phosphate group. The bonds between nucleotides in the chain are formed by deoxyribose and a phosphate group. In the vast majority of cases (except for some viruses containing single-stranded DNA), the DNA macromolecule consists of two chains oriented with nitrogenous bases towards each other. This double-stranded molecule is helical. The overall structure of the DNA molecule is called a “double helix.”
There are four types of nitrogenous bases found in DNA (adenine, guanine, thymine and cytosine). The nitrogenous bases of one of the chains are connected to the nitrogenous bases of the other chain by hydrogen bonds according to the principle of complementarity: adenine connects only with thymine, guanine - only with cytosine. The nucleotide sequence allows you to “encode” information about various types RNA, the most important of which are messenger RNA (mRNA), ribosomal RNA (r RNA) and transport RNA (t RNA). All these types of RNA are synthesized on the template.
Decoding the structure of DNA (1953) was one of the turning points in the history of biology. For their outstanding contributions to this discovery, Francis Crick, James Watson, and Maurice Wilkins were awarded Nobel Prize in Physiology or Medicine 1962
Examination of cells and tissues through an optical microscope.
Tasks for independent completion:
1. Prepare an abstract on the topic “Cell structure”.
2. Prepare a message and electronic presentation on the topic: “Structure and functions of the cell.”
3. Prepare a laboratory report.
form of control independent work:
Protect your presentation and message.
Submitting a laboratory report.
Questions for self-control
A cell is an elementary part of an organism, capable of independent existence, self-reproduction and development. The cell is the basis of the structure and life activity of all living organisms and plants. Cells can exist as independent organisms or as part of multicellular organisms (tissue cells). The term “Cell” was proposed by the English microscopist R. Hooke (1665). The cell is the subject of study of a special branch of biology - cytology. More systematic study of cells began in the nineteenth century. One of the largest scientific theories of that time was the Cell Theory, which asserted the unity of structure of all living nature. The study of all life at the cellular level is at the core of modern biological research. In the structure and functions of each cell, signs are found that are common to all cells, which reflects the unity of their origin from primary organic substances. The particular characteristics of various cells are the result of their specialization in the process of evolution. Thus, all cells regulate metabolism in the same way, double and use their hereditary material, receive and utilize energy. At the same time, different single-celled organisms (amoebas, slippers, ciliates, etc.) differ quite greatly in size, shape, and behavior. The cells of multicellular organisms differ no less sharply. Thus, a person has lymphoid cells - small (about 10 microns in diameter) round cells involved in immunological reactions, and nerve cells, some of which have processes more than a meter long; These cells carry out the main regulatory functions in the body.
Cell structure.
The cells of all organisms have a single structural plan, which clearly shows the commonality of all life processes. Each cell includes two inextricably linked parts: the cytoplasm and the nucleus. Both the cytoplasm and the nucleus are characterized by complexity and strictly ordered structure and, in turn, they include many different structural units that perform very specific functions. Shell. It directly interacts with the external environment and interacts with neighboring cells (in multicellular organisms). The shell is the custom of the cell. She vigilantly ensures that currently unnecessary substances do not penetrate into the cell; on the contrary, the substances that the cell needs can count on its maximum assistance. The core shell is double; consists of inner and outer nuclear membranes. Between these membranes is the perinuclear space. The outer nuclear membrane is usually associated with endoplasmic reticulum channels. The core shell contains numerous pores. They are formed by the closure of the outer and inner membranes and have different diameters. Some nuclei, such as egg nuclei, have many pores and are located at regular intervals on the surface of the nucleus. The number of pores in the nuclear envelope varies in different cell types. The pores are located at an equal distance from each other. Since the diameter of the pore can vary, and in some cases its walls have a rather complex structure, it seems that the pores are contracting, or closing, or, conversely, expanding. Thanks to the pores, the karyoplasm comes into direct contact with the cytoplasm. Quite large molecules of nucleosides, nucleotides, amino acids and proteins easily pass through the pores, and thus an active exchange takes place between the cytoplasm and the nucleus.
