A2. Which scientist discovered the cell? 1) A. Leeuwenhoek 2) T. Schwann 3) R. Hooke 4) R. Virchow
A3. The content of which chemical element predominates in the dry matter of the cell? 1) nitrogen 2) carbon 3) hydrogen 4) oxygen
A4. Which phase of meiosis is shown in the picture? 1) Anaphase I 2) Metaphase I 3) Metaphase II 4) Anaphase II
A5. What organisms are chemotrophs? 1) animals 2) plants 3) nitrifying bacteria 4) fungi A6. The formation of a two-layer embryo occurs during the period of 1) cleavage 2) gastrulation 3) organogenesis 4) postembryonic period
A7. The totality of all the genes of an organism is called 1) genetics 2) gene pool 3) genocide 4) genotype A8. In the second generation with monohybrid crossing and with complete dominance there is a splitting of characteristics in the ratio 1) 3:1 2) 1:2:1 3) 9:3:3:1 4) 1:1
A9. To physical mutagenic factors refers to 1) ultraviolet radiation 2) nitrous acid 3) viruses 4) benzopyrene
A10. In what part of the eukaryotic cell are ribosomal RNAs synthesized? 1) ribosome 2) rough ER 3) nucleolus 4) Golgi apparatus
A11. What is the term for a section of DNA that codes for one protein? 1) codon 2) anticodon 3) triplet 4) gene
A12. Name the autotrophic organism 1) boletus mushroom 2) amoeba 3) tuberculosis bacillus 4) pine
A13. What is nuclear chromatin made of? 1) karyoplasm 2) strands of RNA 3) fibrous proteins 4) DNA and proteins
A14. At what stage of meiosis does crossing over occur? 1) prophase I 2) interphase 3) prophase II 4) anaphase I
A15. What is formed from the ectoderm during organogenesis? 1) notochord 2) neural tube 3) mesoderm 4) endoderm
A16. A non-cellular form of life is 1) euglena 2) bacteriophage 3) streptococcus 4) ciliates
A17. Protein synthesis into mRNA is called 1) translation 2) transcription 3) reduplication 4) dissimilation
A18. In the light phase of photosynthesis, 1) carbohydrate synthesis occurs 2) chlorophyll synthesis 3) absorption carbon dioxide 4) photolysis of water
A19. Cell division with preservation of the chromosome set is called 1) amitosis 2) meiosis 3) gametogenesis 4) mitosis
A20. Plastic metabolism includes 1) glycolysis 2) aerobic respiration 3) assembly of an mRNA chain on DNA 4) breakdown of starch to glucose
A21. Select incorrect statement In prokaryotes, the DNA molecule 1) is closed in a ring 2) is not associated with proteins 3) contains uracil instead of thymine 4) is present in singular
A22. Where does the third stage of catabolism occur - complete oxidation or respiration? 1) in the stomach 2) in mitochondria 3) in lysosomes 4) in the cytoplasm
A23. TO asexual reproduction refers to 1) parthenocarpic formation of fruits in cucumbers 2) parthenogenesis in bees 3) reproduction of tulips by bulbs 4) self-pollination in flowering plants
A24. What organism develops without metamorphosis in the postembryonic period? 1) lizard 2) frog 3) Colorado potato beetle 4) fly
A25. The human immunodeficiency virus affects 1) gonads 2) T-lymphocytes 3) erythrocytes 4) skin and lungs
A26. Cell differentiation begins at the stage 1) blastula 2) neurula 3) zygote 4) gastrula
A27. What are protein monomers? 1) monosaccharides 2) nucleotides 3) amino acids 4) enzymes
A28. In which organelle does the accumulation of substances and the formation of secretory vesicles occur? 1) Golgi apparatus 2) rough ER 3) plastid 4) lysosome
A29. What disease is inherited in a sex-linked manner? 1) deafness 2) diabetes mellitus 3) hemophilia 4) hypertension
A30. Please indicate an incorrect statement. Biological significance meiosis is as follows: 1) increases genetic diversity organisms 2) the stability of the species increases when environmental conditions change 3) the possibility of recombination of characteristics as a result of crossing over appears 4) the likelihood of combinative variability of organisms decreases.
b) oxygen c) carbon d) hydrogen 2. Which chemical element is simultaneously included in the composition of bone tissue and nucleic acids? a) potassium b) phosphorus c) calcium d) zinc 3. When water freezes, the distance between the molecules: a) decreases b) increases c) does not change 4. Children develop rickets with a lack of: a) manganese and iron b) calcium and phosphorus c) copper and zinc d) sulfur and nitrogen 5. Which element is included in the chlorophyll molecule? a) sodium b) potassium c) magnesium d) chlorine 6. Write down from a number of chemical elements: O, C, H, N, Fe, K, S, Zn, Cu, contained in the cell, those that are: a) the basis organic compounds b) macroelements c) microelements 7. Write out from the proposed series of elements: O, Si, Fe, H, C, N, Al, Mg those that predominate: a) in living nature b) in inanimate nature 8. What is the importance of water for vital functions of the cell: a) a medium for chemical elements b) a solvent c) a source of oxygen during photosynthesis Chemical composition of the cell. Organic matter. 1. Which of the following chemical compounds is not a biopolymer? a) protein b) glucose c) DNA d) cellulose 2. From what compounds are hydrocarbons synthesized during photosynthesis? a) from O2 and H2O b) from CO2 and H2 c) from CO2 and H2O d) from CO2 and H2CO3 3. Which product is more advisable to give to a tired marathon runner at a distance to maintain strength? a) A piece of sugar b) a little butter c) a piece of meat d) a little mineral water 4. The ability of camels to tolerate thirst well is explained by the fact that fats: a) retain water in the body b) release water during oxidation c) create a heat-insulating layer that reduces evaporation 5. The largest amount of energy is released during the breakdown of one gram: a) C5H12O5 b) C6H10O6 c) C6H12O6 d) C6H12O5 6. In which case is the formula of the glucose molecule written correctly? a) ether b) alcohol c) water d) hydrochloric acid
Message about the chemical element Cu (copper)1.Meaning of chemical
element for the human body
2.Disadvantage of this element what does it lead to?
3.What does an excess of this element lead to?
4.What foods contain
Today discovered and allocated in pure form There are many chemical elements in the periodic table, and a fifth of them are found in every living organism. They, like bricks, are the main components of organic and inorganic substances.
What chemical elements are included in the composition of the cell, by the biology of what substances one can judge their presence in the body - we will consider all this later in the article.
What is the constancy of chemical composition?
To maintain stability in the body, each cell must maintain the concentration of each of its components at a constant level. This level is determined by species, habitat, and environmental factors.
To answer the question of what chemical elements are included in the composition of a cell, it is necessary to clearly understand that any substance contains any of the components of the periodic table.
Sometimes we're talking about about hundredths and thousandths of a percent of the content of a certain element in a cell, but a change in the said number by even a thousandth can already have serious consequences for the body.
Of the 118 chemical elements in a human cell, there must be at least 24. There are no components that would be found in a living organism, but are not part of inanimate objects nature. This fact confirms the close connection between living and nonliving things in an ecosystem.
The role of various elements that make up the cell
So what chemical elements make up a cell? Their role in the life of the body, it should be noted, directly depends on the frequency of occurrence and their concentration in the cytoplasm. However, despite different content elements in a cell, the significance of each of them in equally high. A deficiency of any of them can lead to a detrimental effect on the body, turning off the most important biochemicals from metabolism. chemical reactions.
When listing what chemical elements make up the human cell, we need to mention three main types, which we will consider further:
Basic biogenic elements of the cell
It is not surprising that the elements O, C, H, N are classified as biogenic, because they form all organic and many non-organic organic matter. It is impossible to imagine proteins, fats, carbohydrates or nucleic acids without these essential components for the body.
The function of these elements determined them high content in organism. Together they account for 98% of the total dry body mass. What else can the activity of these enzymes be manifested in?
- Oxygen. Its content in the cell is about 62% of the total dry mass. Functions: construction of organic and inorganic substances, participation in the respiratory chain;
- Carbon. Its content reaches 20%. Main function: included in all ;
- Hydrogen. Its concentration takes a value of 10%. In addition to the fact that this element is a component of organic matter and water, it also participates in energy transformations;
- Nitrogen. The amount does not exceed 3-5%. Its main role is the formation of amino acids, nucleic acids, ATP, many vitamins, hemoglobin, hemocyanin, chlorophyll.
These are the chemical elements that make up the cell and form most of the substances necessary for normal life.
Importance of Macronutrients
Macronutrients will also help tell you what chemical elements are included in the cell. From the biology course it becomes clear that, in addition to the main ones, 2% of the dry mass consists of other components periodic table. And macroelements include those whose content is not lower than 0.01%. Their main functions are presented in table form.
Calcium (Ca) | Responsible for the contraction of muscle fibers, is part of pectin, bones and teeth. Enhances blood clotting. |
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Phosphorus (P) | It is part of the most important energy source - ATP. |
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Participates in the formation of disulfide bridges during protein folding into a tertiary structure. Part of cysteine and methionine, some vitamins. |
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Potassium ions are involved in cells and also influence the membrane potential. |
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Main anion of the body |
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Sodium (Na) | An analogue of potassium, participating in the same processes. |
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Magnesium (Mg) | Magnesium ions are regulators of the process. In the center of the chlorophyll molecule there is also a magnesium atom. |
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Participates in the transport of electrons along the ETC of respiration and photosynthesis, is structural link myoglobin, hemoglobin and many enzymes. |
We hope that from the above it is not difficult to determine which chemical elements are part of the cell and belong to the macroelements.
Microelements
There are also components of the cell without which the body cannot function normally, but their content is always less than 0.01%. Let's determine which chemical elements are part of the cell and belong to the group of microelements.
It is part of the enzymes DNA and RNA polymerases, as well as many hormones (for example, insulin). |
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Participates in the processes of photosynthesis, hemocyanin synthesis and some enzymes. |
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It is a structural component of the hormones T3 and T4 thyroid gland |
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Manganese (Mn) | less than 0.001 | Included in enzymes and bones. Participates in nitrogen fixation in bacteria |
less than 0.001 | Affects the process of plant growth. |
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Part of bones and tooth enamel. |
Organic and inorganic substances
In addition to those listed, what other chemical elements are included in the composition of the cell? The answers can be found by simply studying the structure of most substances in the body. Among them, molecules of organic and inorganic origin are distinguished, and each of these groups contains a fixed set of elements.
The main classes of organic substances are proteins, nucleic acids, fats and carbohydrates. They are built entirely from basic nutrients: the skeleton of the molecule is always formed by carbon, and hydrogen, oxygen and nitrogen are part of the radicals. In animals, the dominant class is proteins, and in plants, polysaccharides.
Inorganic substances are all mineral salts and, of course, water. Among all the inorganics in the cell, the most is H 2 O, in which the remaining substances are dissolved.
All of the above will help you determine what chemical elements are part of the cell, and their functions in the body will no longer be a mystery to you.
>> Chemistry: Chemical elements in the cells of living organisms
More than 70 elements have been discovered in the substances that form the cells of all living organisms (humans, animals, plants). These elements are usually divided into two groups: macroelements and microelements.
Macroelements are found in cells in large quantities. First of all, these are carbon, oxygen, nitrogen and hydrogen. Together they make up almost 98% of the total contents of the cell. In addition to these elements, macroelements also include magnesium, potassium, calcium, sodium, phosphorus, sulfur and chlorine. Their total content is 1.9%. Thus, the share of other chemical elements accounts for about 0.1%. These are microelements. These include iron, zinc, manganese, boron, copper, iodine, cobalt, bromine, fluorine, aluminum, etc.
23 trace elements were found in mammalian milk: lithium, rubidium, copper, silver, barium, strontium, titanium, arsenic, vanadium, chromium, molybdenum, iodine, fluorine, manganese, iron, cobalt, nickel, etc.
The blood of mammals contains 24 trace elements, and the human brain contains 18 trace elements.
As you can see, there are no special elements in the cell that are characteristic only of living nature, i.e. atomic level There are no differences between living and inanimate nature. These differences are found only at the level complex substances- on molecular level. Thus, along with inorganic substances (water and mineral salts), the cells of living organisms contain substances characteristic only of them - organic substances (proteins, fats, carbohydrates, nucleic acids, vitamins, hormones, etc.). These substances are built mainly from carbon, hydrogen, oxygen and nitrogen, i.e. from macroelements. Microelements are contained in these substances in small quantities, however, their role in the normal functioning of organisms is enormous. For example, compounds of boron, manganese, zinc, cobalt sharply increase the yield of individual agricultural plants and increase their resistance to various kinds diseases.
Humans and animals receive the microelements they need for normal life through the plants they eat. If there is not enough manganese in food, then growth retardation, delayed puberty, and metabolic disorders during the formation of the skeleton are possible. Adding fractions of a milligram of manganese salts to the daily diet of animals eliminates these diseases.
Cobalt is part of vitamin B12, which is responsible for the functioning of blood-forming organs. Lack of cobalt in food often causes serious illness, which leads to depletion of the body and even death.
The importance of microelements for humans was first revealed during the study of a disease such as endemic goiter, which was caused by a lack of iodine in food and water. Taking salt containing iodine leads to recovery, and adding it to food in small quantities prevents disease. For this purpose, table salt is iodized, to which 0.001-0.01% potassium iodide is added.
Most biological enzyme catalysts contain zinc, molybdenum and some other metals. These elements, contained in very small quantities in the cells of living organisms, ensure the normal functioning of the finest biochemical mechanisms and are true regulators of vital processes.
Many microelements are contained in vitamins - organic substances of various chemical nature, entering the body with food in small doses and having a great impact on metabolism and the general functioning of the body. In my own way biological effect they are close to enzymes, but enzymes are formed by the body's cells, and vitamins usually come from food. Sources of vitamins are plants: citrus fruits, rose hips, parsley, onions, garlic and many others. Some vitamins - A, B1, B2, K - are obtained synthetically. Vitamins got their name from two words: vita - life and amine - containing nitrogen.
Microelements are also part of hormones - biologically active substances regulating the functioning of organs and organ systems of humans and animals. They take their name from Greek word Harmao - I win. Hormones are produced by the endocrine glands and enter the blood, which carries them throughout the body. Some hormones are obtained synthetically.
1. Macroelements and microelements.
2. The role of microelements in the life of plants, animals and humans.
3. Organic substances: proteins, fats, carbohydrates.
4. Enzymes.
5. Vitamins.
6. Hormones.
At what level of forms of existence of a chemical element does the difference between living and inanimate nature begin?
Why are individual macroelements also called biogenic? List them.
Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework controversial issues rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for a year guidelines discussion programs Integrated LessonsAll organisms on our planet consist of cells that are similar in chemical composition. In this article we will briefly talk about the chemical composition of the cell, its role in the life of the entire organism, and find out what science studies this issue.
Groups of elements of the chemical composition of the cell
The science that studies the components and structure of a living cell is called cytology.
All elements included in chemical structure organism can be divided into three groups:
- macroelements;
- microelements;
- ultramicroelements.
Macroelements include hydrogen, carbon, oxygen and nitrogen. They account for almost 98% of all constituent elements.
Microelements are present in tenths and hundredths of a percent. And a very low content of ultramicroelements - hundredths and thousandths of a percent.
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Translated from Greek, “macro” means big, and “micro” means small.
Scientists have found that there are no special elements that are unique to living organisms. Therefore, both living and inanimate nature consists of the same elements. This proves their relationship.
Despite the quantitative content of a chemical element, the absence or reduction of at least one of them leads to the death of the entire organism. After all, each of them has its own meaning.
The role of the chemical composition of the cell
Macroelements are the basis of biopolymers, namely proteins, carbohydrates, nucleic acids and lipids.
Microelements are part of vital organic substances and participate in metabolic processes. They are constituent components of mineral salts, which are in the form of cations and anions, their ratio determines alkaline environment. Most often it is slightly alkaline, because the ratio of mineral salts does not change.
Hemoglobin contains iron, chlorophyll - magnesium, proteins - sulfur, nucleic acids - phosphorus, metabolism occurs with a sufficient amount of calcium.
Rice. 2. Cell composition
Some chemical elements are components of inorganic substances, such as water. She plays big role in the life activity of both plants and animal cell. Water is a good solvent, because of this all substances inside the body are divided into:
- Hydrophilic - dissolves in water;
- Hydrophobic - do not dissolve in water.
Thanks to the presence of water, the cell becomes elastic and promotes the movement of organic substances in the cytoplasm.
Rice. 3. Cell substances.
Table “Properties of the chemical composition of the cell”
To clearly understand what chemical elements are part of the cell, we included them in the following table:
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Elements |
Meaning |
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Macronutrients |
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Oxygen, carbon, hydrogen, nitrogen |
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A constituent component of the shell in plants, in the animal body it is found in bones and teeth, and takes an active part in blood clotting. |
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Contained in nucleic acids, enzymes, bone tissue and tooth enamel. |
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Microelements |
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It is the basis of proteins, enzymes and vitamins. |
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Provides transmission nerve impulses, activates protein synthesis, photosynthesis and growth processes. |
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One of the components gastric juice, enzyme provocateur. |
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Takes an active part in metabolic processes, a component of the thyroid hormone. |
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Provides transmission of impulses to nervous system, maintains constant pressure inside the cell, provokes the synthesis of hormones. |
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A constituent element of chlorophyll, bone tissue and teeth, provokes DNA synthesis and heat transfer processes. |
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An integral part of hemoglobin, the lens, and the cornea, it synthesizes chlorophyll. Transports oxygen throughout the body. |
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Ultramicroelements |
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An integral part of the processes of blood formation and photosynthesis, it accelerates intracellular oxidation processes. |
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Manganese |
Activates photosynthesis, participates in blood formation, and ensures high productivity. |
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Component of tooth enamel. |
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Regulates plant growth. |
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What have we learned?
Each cell of living nature has its own set of chemical elements. By their composition, objects are living and inanimate nature have similarities, this proves their close relationship. Each cell consists of macroelements, microelements and ultramicroelements, each of which has its own role. The absence of at least one of them leads to illness and even death of the entire organism.
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The cell is the elementary unit of life on Earth. It has all the characteristics of a living organism: it grows, reproduces, exchanges substances and energy with the environment, reacts to external stimuli. The beginning of biological evolution is associated with the appearance of cellular life forms on Earth. Unicellular organisms are cells that exist separately from each other. The body of all multicellular organisms - animals and plants - is built from a greater or lesser number of cells, which are a kind of blocks that make up a complex organism. Regardless of whether a cell is an integral living system - a separate organism or constitutes only a part of it, it is endowed with a set of characteristics and properties common to all cells.
Chemical composition of the cell
About 60 elements were found in cells periodic table Mendeleev, which are also found in inanimate nature. This is one of the proofs of the commonality of living and inanimate nature. In living organisms, the most abundant are hydrogen, oxygen, carbon and nitrogen, which make up about 98% of the mass of cells. This is due to the peculiar chemical properties of hydrogen, oxygen, carbon and nitrogen, as a result of which they turned out to be most suitable for the formation of molecules that perform biological functions. These four elements are capable of forming very strong covalent bonds by pairing electrons belonging to two atoms. Covalently bonded carbon atoms can form the framework of countless different organic molecules. Since carbon atoms easily form covalent bonds with oxygen, hydrogen, nitrogen, and sulfur, organic molecules achieve exceptional complexity and structural diversity.
In addition to the four main elements, the cell contains noticeable quantities (10th and 100th fractions of a percent) of iron, potassium, sodium, calcium, magnesium, chlorine, phosphorus and sulfur. All other elements (zinc, copper, iodine, fluorine, cobalt, manganese, etc.) are found in the cell in very small quantities and are therefore called trace elements.
Chemical elements are part of inorganic and organic compounds. Inorganic compounds include water, mineral salts, carbon dioxide, acids and bases. Organic compounds are proteins, nucleic acids, carbohydrates, fats (lipids) and lipoids. In addition to oxygen, hydrogen, carbon and nitrogen, they may contain other elements. Some proteins contain sulfur. Phosphorus is a component of nucleic acids. The hemoglobin molecule includes iron, magnesium is involved in the construction of the chlorophyll molecule. Microelements, despite their extremely low content in living organisms, play important role in life processes. Iodine is part of the thyroid hormone - thyroxine, cobalt is part of vitamin B 12, the hormone of the islet part of the pancreas - insulin - contains zinc. In some fish, copper takes the place of iron in the oxygen-carrying pigment molecules.
Inorganic substances
Water. H 2 O is the most common compound in living organisms. Its content in different cells varies quite widely: from 10% in tooth enamel to 98% in the body of a jellyfish, but on average it makes up about 80% of body weight. The extremely important role of water in supporting life processes is due to its physical and chemical properties. Molecular polarity and ability to form hydrogen bonds make water a good solvent for a huge number of substances. Most chemical reactions occurring in a cell can only occur in aqueous solution. Water is also involved in many chemical transformations.
The total number of hydrogen bonds between water molecules varies depending on t °. At t ° When ice melts, approximately 15% of hydrogen bonds are destroyed, at t° 40°C - half. Upon transition to the gaseous state, all hydrogen bonds are destroyed. This explains the high specific heat water. When the temperature of the external environment changes, water absorbs or releases heat due to the rupture or new formation of hydrogen bonds. In this way, fluctuations in temperature inside the cell turn out to be smaller than in environment. The high heat of evaporation underlies the efficient mechanism of heat transfer in plants and animals.
Water as a solvent takes part in the phenomena of osmosis, which plays an important role in the life of the body's cells. Osmosis is the penetration of solvent molecules through a semi-permeable membrane into a solution of a substance. Semi-permeable membranes are those that allow solvent molecules to pass through, but do not allow solute molecules (or ions) to pass through. Therefore, osmosis is the one-way diffusion of water molecules in the direction of the solution.
Mineral salts. Most of the inorganic substances in cells are in the form of salts in a dissociated or solid state. The concentration of cations and anions in the cell and in its environment is not the same. The cell contains quite a lot of K and a lot of Na. In the extracellular environment, for example in blood plasma, in sea water, on the contrary, there is a lot of sodium and little potassium. Cell irritability depends on the ratio of concentrations of Na +, K +, Ca 2+, Mg 2+ ions. In the tissues of multicellular animals, K is part of the multicellular substance that ensures the cohesion of cells and their ordered arrangement. The osmotic pressure in the cell and its buffering properties largely depend on the concentration of salts. Buffering is the ability of a cell to maintain the slightly alkaline reaction of its contents at a constant level. Buffering inside the cell is provided mainly by H 2 PO 4 and HPO 4 2- ions. In extracellular fluids and blood, the role of a buffer is played by H 2 CO 3 and HCO 3 -. Anions bind H ions and hydroxide ions (OH -), due to which the reaction inside the cell of extracellular fluids remains virtually unchanged. Insoluble mineral salts (for example, Ca phosphate) provide strength to the bone tissue of vertebrates and mollusk shells.
Organic cell matter
Squirrels. Among the organic substances of the cell, proteins are in first place both in quantity (10–12% of the total mass of the cell) and in importance. Proteins are high molecular weight polymers (with molecular weight from 6000 to 1 million and above), the monomers of which are amino acids. Living organisms use 20 amino acids, although there are many more. The composition of any amino acid includes an amino group (-NH 2), which has basic properties, and a carboxyl group (-COOH), which has acidic properties. Two amino acids are combined into one molecule by establishing an HN-CO bond, releasing a water molecule. The bond between the amino group of one amino acid and the carboxyl group of another is called a peptide bond. Proteins are polypeptides containing tens and hundreds of amino acids. Molecules of various proteins differ from each other in molecular weight, number, composition of amino acids and the sequence of their location in the polypeptide chain. It is therefore clear that proteins are extremely diverse; their number in all types of living organisms is estimated at 10 10 - 10 12.
A chain of amino acid units connected covalently by peptide bonds in a specific sequence is called primary structure squirrel. In cells, proteins look like spirally twisted fibers or balls (globules). This is explained by the fact that in natural protein the polypeptide chain is laid out in a strictly defined way, depending on chemical structure the amino acids it contains.
First, the polypeptide chain folds into a spiral. Attraction occurs between atoms of neighboring turns and hydrogen bonds are formed, in particular, between NH- and CO groups, located on adjacent turns. A chain of amino acids, twisted in the form of a spiral, forms the secondary structure of the protein. As a result of further folding of the helix, a configuration specific to each protein arises, called the tertiary structure. The tertiary structure is due to the action of cohesion forces between hydrophobic radicals found in some amino acids and covalent bonds between the SH groups of the amino acid cysteine ( S-S-connections). The number of amino acids with hydrophobic radicals and cysteine, as well as the order of their arrangement in the polypeptide chain, are specific to each protein. Consequently, the features of the tertiary structure of a protein are determined by its primary structure. The protein exhibits biological activity only in the form of a tertiary structure. Therefore, replacing even one amino acid in a polypeptide chain can lead to a change in the configuration of the protein and to a decrease or loss of its biological activity.
In some cases, protein molecules combine with each other and can only perform their function in the form of complexes. Thus, hemoglobin is a complex of four molecules and only in this form is it capable of attaching and transporting oxygen. Such aggregates represent the quaternary structure of the protein. Based on their composition, proteins are divided into two main classes - simple and complex. Simple proteins consist only of amino acids, nucleic acids (nucleotides), lipids (lipoproteins), Me (metalloproteins), P (phosphoproteins).
The functions of proteins in a cell are extremely diverse. One of the most important is the construction function: proteins are involved in the formation of all cell membranes and cell organelles, as well as intracellular structures. Exclusively important has an enzymatic (catalytic) role of proteins. Enzymes accelerate chemical reactions occurring in the cell by 10 and 100 million times. Motor function is provided by special contractile proteins. These proteins are involved in all types of movements that cells and organisms are capable of: the flickering of cilia and the beating of flagella in protozoa, muscle contraction in animals, the movement of leaves in plants, etc. The transport function of proteins is to attach chemical elements (for example, hemoglobin adds O) or biologically active substances (hormones) and transfer them to the tissues and organs of the body. The protective function is expressed in the form of the production of special proteins, called antibodies, in response to the penetration of foreign proteins or cells into the body. Antibodies bind and neutralize foreign substances. Proteins play an important role as sources of energy. With complete splitting 1g. 17.6 kJ (~4.2 kcal) of proteins are released.
Carbohydrates. Carbohydrates, or saccharides, are organic substances with general formula(CH 2 O) n. Most carbohydrates have twice the number of H atoms more number O atoms, as in water molecules. That's why these substances were called carbohydrates. In a living cell, carbohydrates are found in quantities not exceeding 1-2, sometimes 5% (in the liver, in the muscles). Richest in carbohydrates plant cells, where their content in some cases reaches 90% of the dry matter mass (seeds, potato tubers, etc.).
Carbohydrates are simple and complex. Simple carbohydrates are called monosaccharides. Depending on the number of carbohydrate atoms in the molecule, monosaccharides are called trioses, tetroses, pentoses or hexoses. Of the six carbon monosaccharides - hexoses - the most important are glucose, fructose and galactose. Glucose is contained in the blood (0.1-0.12%). The pentoses ribose and deoxyribose are found in nucleic acids and ATP. If two monosaccharides are combined in one molecule, the compound is called a disaccharide. Table sugar, obtained from cane or sugar beets, consists of one molecule of glucose and one molecule of fructose, milk sugar - of glucose and galactose.
Complex carbohydrates formed from many monosaccharides are called polysaccharides. The monomer of polysaccharides such as starch, glycogen, cellulose is glucose. Carbohydrates perform two main functions: construction and energy. Cellulose forms the walls of plant cells. The complex polysaccharide chitin serves as the main structural component of the exoskeleton of arthropods. Chitin also performs a construction function in fungi. Carbohydrates play the role of the main source of energy in the cell. During the oxidation of 1 g of carbohydrates, 17.6 kJ (~4.2 kcal) is released. Starch in plants and glycogen in animals are deposited in cells and serve as an energy reserve.
Nucleic acids. The importance of nucleic acids in a cell is very great. The peculiarities of their chemical structure provide the possibility of storing, transferring and inheriting to daughter cells information about the structure of protein molecules that are synthesized in each tissue at a certain stage individual development. Since most of the properties and characteristics of cells are due to proteins, it is clear that the stability of nucleic acids is the most important condition normal functioning of cells and whole organisms. Any changes in the structure of cells or the activity of physiological processes in them, thus affecting vital activity. The study of the structure of nucleic acids is extremely important for understanding the inheritance of traits in organisms and the patterns of functioning of both individual cells and cellular systems - tissues and organs.
There are 2 types of nucleic acids – DNA and RNA. DNA is a polymer consisting of two nucleotide helices arranged to form a double helix. Monomers of DNA molecules are nucleotides consisting of a nitrogenous base (adenine, thymine, guanine or cytosine), a carbohydrate (deoxyribose) and a phosphoric acid residue. The nitrogenous bases in the DNA molecule are connected to each other by an unequal number of H-bonds and are arranged in pairs: adenine (A) is always against thymine (T), guanine (G) against cytosine (C). Schematically, the arrangement of nucleotides in a DNA molecule can be depicted as follows:
Fig. 1. Location of nucleotides in a DNA molecule
From Fig.1. it is clear that the nucleotides are connected to each other not randomly, but selectively. The ability for selective interaction of adenine with thymine and guanine with cytosine is called complementarity. The complementary interaction of certain nucleotides is explained by the peculiarities of the spatial arrangement of atoms in their molecules, which allow them to come closer and form H-bonds. In a polynucleotide chain, neighboring nucleotides are linked to each other through a sugar (deoxyribose) and a phosphoric acid residue. RNA, like DNA, is a polymer whose monomers are nucleotides. The nitrogenous bases of three nucleotides are the same as those that make up DNA (A, G, C); the fourth - uracil (U) - is present in the RNA molecule instead of thymine. RNA nucleotides differ from DNA nucleotides in the structure of the carbohydrate they contain (ribose instead of deoxyribose).
In a chain of RNA, nucleotides are connected by forming covalent bonds between the ribose of one nucleotide and the phosphoric acid residue of another. The structure differs between two-stranded RNA. Double-stranded RNAs are the custodians of genetic information in a number of viruses, i.e. They perform the functions of chromosomes. Single-stranded RNA transfers information about the structure of proteins from the chromosome to the place of their synthesis and participates in protein synthesis.
There are several types of single-stranded RNA. Their names are determined by their function or location in the cell. Most Cytoplasmic RNA (up to 80-90%) is ribosomal RNA (rRNA), contained in ribosomes. rRNA molecules are relatively small and consist of an average of 10 nucleotides. Another type of RNA (mRNA) that carries information about the sequence of amino acids in proteins that must be synthesized to ribosomes. The size of these RNAs depends on the length of the DNA region from which they were synthesized. Transfer RNAs perform several functions. They deliver amino acids to the site of protein synthesis, “recognize” (by the principle of complementarity) the triplet and RNA corresponding to the transferred amino acid, and carry out the precise orientation of the amino acid on the ribosome.
Fats and lipoids. Fats are compounds of fatty high molecular weight acids and trihydric alcohol glycerol. Fats do not dissolve in water - they are hydrophobic. There are always other complex hydrophobic fat-like substances called lipoids in the cell. One of the main functions of fats is energy. During the breakdown of 1 g of fats to CO 2 and H 2 O, a large number of energy – 38.9 kJ (~9.3 kcal). The fat content in the cell ranges from 5-15% of the dry matter mass. In living tissue cells, the amount of fat increases to 90%. The main function of fats in the animal (and partly plant) world is storage.
When 1 g of fat is completely oxidized (to carbon dioxide and water), about 9 kcal of energy is released. (1 kcal = 1000 cal; calorie (cal, cal) - a non-systemic unit of the amount of work and energy, equal to the quantity heat required to heat 1 ml of water by 1 °C at standard atmospheric pressure 101.325 kPa; 1 kcal = 4.19 kJ). When 1 g of proteins or carbohydrates is oxidized (in the body), only about 4 kcal/g is released. In a wide variety of aquatic organisms - from single-celled diatoms to giant sharks - the fat will “float”, reducing average density bodies. The density of animal fats is about 0.91-0.95 g/cm³. The density of vertebrate bone tissue is close to 1.7-1.8 g/cm³, and the average density of most other tissues is close to 1 g/cm³. It is clear that you need quite a lot of fat to “balance” a heavy skeleton.
Fats and lipids also perform a construction function: they are part of cell membranes. Due to poor thermal conductivity, fat is capable of protective function. In some animals (seals, whales) it is deposited in the subcutaneous adipose tissue, forming a layer up to 1 m thick. The formation of some lipoids precedes the synthesis of a number of hormones. Consequently, these substances also have the function of regulating metabolic processes.