The cell consists of organic and mineral substances.
Mineral composition of cells
Of the inorganic substances, the cell composition includes 86 elements of the Periodic Table, about 16-18 elements are vital for the normal existence of a living cell.
Among the elements there are: organogens, macroelements, microelements and ultramicroelements.
Organogens
These are the substances that make up organic matter: oxygen, carbon, hydrogen and nitrogen.
Oxygen(65-75%) - found in a huge number of organic molecules - proteins, fats, carbohydrates, nucleic acids. In the form of a simple substance (O2), it is formed during oxygenic photosynthesis (cyanobacteria, algae, plants).
Functions: 1. Oxygen is a strong oxidizing agent (oxidizes glucose during cellular respiration, energy is released in the process)
2. Part of the organic substances of the cell
3. Part of the water molecule
Carbon(15-18%) - is the basis of the structure of all organic substances. Carbon dioxide is released during respiration and absorbed during photosynthesis. It can be in the form of CO - carbon monoxide. In the form of calcium carbonate (CaCO3) it is part of bones.
Hydrogen(8 - 10%) - like carbon, it is part of any organic compound. It is also part of the water.
Nitrogen(2 - 3%) - is part of amino acids, and therefore proteins, nucleic acids, some vitamins and pigments. Fixed by bacteria from the atmosphere.
Macronutrients
Magnesium (0,02 - 0,03%)
1. In the cell - part of enzymes, involved in DNA synthesis and energy metabolism
2. In plants - part of chlorophyll
3. In animals - part of the enzymes involved in the functioning of muscle, nervous and bone tissues.
Sodium (0,02 - 0,03%)
1. In the cell - part of potassium-sodium channels and pumps
2. In plants - participates in osmosis, which ensures the absorption of water from the soil
3. In animals - participates in kidney function, maintaining heart rhythm, is part of the blood (NaCl), helps maintain acid-base balance
Calcium (0,04 - 2,0%)
1. In the cell - participates in the selective permeability of the membrane, in the process of connecting DNA with proteins
2. In plants - forms salts of pectin substances, imparts hardness to the intercellular substance connecting plant cells, and also participates in the formation of intercellular contacts
3. In animals - is part of the bones of vertebrates, shells of mollusks and coral polyps, participates in the formation of bile, increases the reflex excitability of the spinal cord and the center of salivation, participates in the synaptic transmission of nerve impulses, in blood clotting processes, is a necessary factor in the reduction of striated muscles
Iron (0,02%)
1. In the cell - part of cytochromes
2. In plants - participates in the synthesis of chlorophyll, is part of enzymes involved in respiration, is part of cytochromes
3. In animals - part of hemoglobin
Potassium (0,15 - 0,4%)
1. In the cell - maintains the colloidal properties of the cytoplasm, is part of potassium-sodium pumps and channels, activates enzymes involved in protein synthesis during glycolysis
2. In plants - participates in the regulation of water metabolism and photosynthesis
3. Necessary for proper heart rhythm, participates in the conduction of nerve impulses
Sulfur (0,15 - 0,2%)
1. In the cell - it is part of some amino acids - citine, cysteine and methionine, forms disulfide bridges in the tertiary structure of protein, is part of some enzymes and coenzyme A, is part of bacteriochlorophyll, some chemosynthetics use sulfur compounds to produce energy
2. In animals - part of insulin, vitamin B1, biotin
Phosphorus (0,2 - 1,0%)
1. In the cell - in the form of phosphoric acid residues it is part of DNA, RNA, ATP, nucleotides, coenzymes NAD, NADP, FAD, phosphorylated sugars, phospholipids and many enzymes; it forms membranes as part of phospholipids
2. In animals - part of bones, teeth, in mammals it is a component of the buffer system, maintains the acid balance of tissue fluid relatively constant
Chlorine (0,05 - 0,1%)
1. In the cell - participates in maintaining the electroneutrality of the cell
2. In plants - participates in the regulation of turgor pressure
3. In animals - participates in the formation of the osmotic potential of blood plasma, as well as in the processes of excitation and inhibition in nerve cells, is part of the gastric juice in the form of hydrochloric acid
Microelements
Copper
1. In the cell - part of the enzymes involved in the synthesis of cytochromes
2. In plants - part of the enzymes involved in the reactions of the dark phase of photosynthesis
3. In animals - participates in the synthesis of hemoglobin, in invertebrates it is part of hemocyanins - oxygen carriers, in humans - it is part of the skin pigment - melanin
Zinc
1. Participates in alcoholic fermentation
2. In plants - part of the enzymes involved in the breakdown of carbonic acid and in the synthesis of plant hormones-auxins
Iodine
1. In vertebrates - part of the thyroid hormones (thyroxine)
Cobalt
1. In animals - part of vitamin B12 (takes part in the synthesis of hemoglobin), its deficiency leads to anemia
Fluorine
1. In animals - gives strength to bones and tooth enamel
Manganese
1. In the cell - part of enzymes involved in respiration, fatty acid oxidation, increases carboxylase activity
2. In plants - as part of enzymes, it participates in dark reactions of photosynthesis and in the reduction of nitrates
3. In animals - part of the phosphatase enzymes necessary for bone growth
Bromine
1. In the cell - part of vitamin B1, which is involved in the breakdown of pyruvic acid
Molybdenum
1. In the cell - as part of enzymes, it participates in the fixation of atmospheric nitrogen
2. In plants - as part of enzymes, it participates in the work of stomata and enzymes involved in the synthesis of amino acids
Bor
1. Affects plant growth
1. What substances are called mineral?
Answer. Minerals are chemical elements necessary for a living organism to ensure normal functioning (calcium, phosphorus, potassium, magnesium)
Magnesium is a vital element; its participation helps muscles relax. Magnesium inhibits the excitation of nerve endings, participates in many catalytic processes, has the ability to stimulate intestinal motility, thereby promoting the removal of toxins (including cholesterol) and increasing the secretion of bile. Magnesium has a vasodilating effect and improves blood supply to the heart muscle.
Potassium is a mineral that is necessary for the normal functioning of cells of the peripheral and central nervous system, to maintain osmotic pressure, and for the normal functioning of all muscles. They help remove water from the body, and therefore harmful metabolic products.
Sodium. Table salt is necessary for our body. It is a component of blood and tissue fluid. The necessary amount enters the body with food.
Phosphorus is an essential element that is part of nucleic acid proteins and bone tissue; It affects growth and restoration processes in tissues. Phosphorus is needed for bones and is also needed in muscles. The human energy accumulator is adenosine triphosphoric acid (ATP). When a person works, this acid disintegrates, releasing the energy contained in it.
A vital element is sulfur, the significance of which is primarily determined by the fact that it is included in proteins in the form of sulfur-containing amino acids (cysteine and methionine), as well as in the composition of some hormones and vitamins. A person's need for sulfur is satisfied (about 1 g per day) with a normal daily diet.
Chlorine is also a vital element that is involved in the formation of gastric juice, forms plasma, and activates a number of enzymes. The chlorine content in food products ranges from 2-160 mg/%. Without the addition of table salt, the diet would contain 1.6 g of chlorine.
Iron is necessary for hematopoiesis; it ensures the transport of oxygen from the lungs to the tissues. Iron is part of hemoglobin - the red pigment of blood. Red blood cells are formed in the bone marrow; They enter the blood and circulate in it for 6 weeks. They then disintegrate into their component parts, and the iron contained in them enters the spleen and liver, depositing there “until required.”
Zinc is found in blood and muscle tissue. This element is necessary, the significance of which is determined by the fact that it is part of the pancreatic hormone insulin, which regulates blood sugar levels. It is also important for complete wound healing, participates in the regulation of blood pressure and promotes the formation of prostaglandins, which have an anti-inflammatory effect; helps remove cholesterol from the body.
2. What process is called dissociation?
Answer. Electrolytic dissociation is the process of decomposition of an electrolyte into ions when it is dissolved in water or upon melting.
Dissociation into ions occurs due to the interaction of a solute with a solvent; According to spectroscopic methods, this interaction is largely chemical in nature. Along with the solvating ability of solvent molecules, a certain role in electrolytic dissociation is also played by the macroscopic property of the solvent - its dielectric constant
3. What are ions?
Answer. An ion is a particle in which the total number of protons is not equivalent to the total number of electrons. An ion in which the total number of protons is greater than the total number of electrons has a positive charge and is called a cation. An ion in which the total number of protons is less than the total number of electrons has a negative charge and is called an anion.
In the form of independent particles, ions are found in all aggregate states of matter: in gases (in particular, in the atmosphere), in liquids (in melts and solutions), in crystals and in plasma (in particular, in interstellar space).
Questions after §8
1. In what form are minerals present in living organisms?
Answer. Most of the mineral substances of the cell are in the form of salts, dissociated into ions, or in the solid state.
In the cytoplasm of almost any cell there are crystalline inclusions, usually consisting of slightly soluble calcium and phosphorus salts. In addition to them, they may contain silicon dioxide and other inorganic substances. They are used to form supporting structures of the cell (for example, the mineral skeleton of radiolarians) and the body - the mineral substance of bone tissue (calcium and phosphorus salts), mollusk shells (calcium salts), chitin (calcium salts), etc.
2. What is the role of inorganic ions in the cell?
Answer. Inorganic ions, which are of no small importance for ensuring the vital processes of the cell, are represented by cations (K+, Na+, Ca2+, Mg2+, NH) and anions (Cl-, HPO, H2PO, HCO, NO, PO, CO) of mineral salts. The concentration of cations and anions in the cell and in its environment is different. As a result, a potential difference is formed between the contents of the cell and its surrounding environment, providing such important processes as irritability and transmission of excitation along a nerve or muscle.
3. What is the role of ions in the body’s buffer systems?
Answer. The constant pH in cells is maintained due to the buffering properties of their contents. A buffer solution is a solution containing a mixture of a weak acid and its soluble salt. When acidity (the concentration of H+ ions) increases, the free anions that come from the salt readily combine with the free H+ ions and remove them from solution. When acidity decreases, additional H+ ions are released. This way, a relatively constant concentration of H+ ions is maintained in the buffer solution. Some organic compounds, in particular proteins, also have buffering properties.
Being components of the body's buffer systems, ions determine their properties - the ability to maintain pH at a constant level (close to a neutral reaction), despite the fact that acidic and alkaline products are continuously formed during the metabolic process. Thus, the phosphate buffer system of mammals, consisting of HPO42- and H2PO4-, maintains the pH of the intracellular fluid in the range of 6.9–7.4. The main buffer system of the extracellular environment (blood plasma) is the bicarbonate system, consisting of H2CO3 and HCO4- and maintaining a pH of 7.4
4. Why does the lack or absence of certain metal ions lead to disruption of cell functioning?
Answer. Ions of some metals (Mg, Ca, Fe, Zn, Cu, Mn, Mo, Br, Co) are components of many enzymes, hormones and vitamins or activate them. For example, the Fe ion is part of blood hemoglobin, and the Zn ion is part of the hormone insulin. With their deficiency, the most important processes of cell life are disrupted.
Inorganic ions, or minerals, perform the following functions in the body:
1. Bioelectric function. This function is associated with the occurrence of a potential difference on cell membranes. The ion concentration gradient on both sides of the membrane creates a potential of about 60-80 mV in different cells. The inner side of the cell membrane is negatively charged relative to the outer. The higher the electrical potential of the membrane, the higher the protein content and its ionization (negative charge) inside the cell and the concentration of cations outside the cell (the diffusion of Na + and K + ions through the membrane into the cell is difficult). This function of inorganic ions is used to regulate the functions of especially excitable cells (nerve, muscle) and to conduct nerve impulses.
2. Osmotic function used to regulate osmotic pressure. A living cell obeys the law of isosmopolarity: in all environments of the body, between which there is a free exchange of water, the same osmotic pressure is established. If the number of ions in a certain medium increases, then water rushes after them until a new equilibrium and a new level of osmotic pressure are established.
3. Structural function due to the complexing properties of metals. Metal ions interact with anionic groups of proteins, nucleic acids and other macromolecules and thereby ensure, along with other factors, the maintenance of certain conformations of these molecules. Since the biological activity of biopolymers depends on their conformations, the normal implementation of their functions by proteins, the unhindered implementation of information contained in nucleic acids, the formation of supramolecular complexes, the formation of subcellular structures and other processes are unthinkable without the participation of cations and anions.
4. Regulatory function is that metal ions are enzyme activators and thereby regulate the rate of chemical transformations in the cell. This is a direct regulatory effect of cations. Indirectly, metal ions are often necessary for the action of another regulator, for example, a hormone. Let's give a few examples. The formation of the active form of insulin is impossible without zinc ions. The tertiary structure of RNA is largely determined by the ionic strength of the solution, and cations such as Cr 2+, Ni 2+, Fe 2+, Zn 2+, Mn 2+ and others are directly involved in the formation of the helical structure of nucleic acids. The concentration of Mg 2+ ions affects the formation of such a supramolecular structure as ribosomes.
5. Transport function manifests itself in the participation of certain metals (as part of metalloproteins) in the transfer of electrons or simple molecules. For example, iron and copper cations are part of cytochromes, which are carriers of electrons in the respiratory chain, and iron in hemoglobin binds oxygen and participates in its transfer.
6. Energy function associated with the use of phosphate anions in the formation of ATP and ADP (ATP is the main carrier of energy in living organisms).
7. Mechanical function. For example, the Ca +2 cation and phosphate anion are part of the hydroxylapatite and calcium phosphate of bones and determine their mechanical strength.
8. Synthetic function. Many inorganic ions are used in the synthesis of complex molecules. For example, iodine ions I¯ are involved in the synthesis of iodothyronines in thyroid cells; anion (SO 4) 2- - in the synthesis of ester-sulfur compounds (during the neutralization of harmful organic alcohols and acids in the body). Selenium is important in the mechanism of protection against the toxic effects of peroxide. It forms selenocysteine, an analogue of cysteine, in which selenium atoms replace sulfur atoms. Selenocysteine is a component of the enzyme glutathione peroxidase, which catalyzes the reduction of hydrogen peroxide with glutathione (tripeptide - γ-glutamyl-cysteinylglycine)
It is important to note that, within certain limits, interchangeability of some ions is possible. If there is a deficiency of a metal ion, it can be replaced by another metal ion that is similar in physicochemical properties and ionic radius. For example, the sodium ion is replaced by a lithium ion; calcium ion - strontium ion; molybdenum ion - vanadium ion; iron ion - cobalt ion; sometimes magnesium ions - manganese ions.
Due to the fact that minerals activate the action of enzymes, they affect all aspects of metabolism. Let us consider how the metabolism of nucleic acids, proteins, carbohydrates and lipids depends on the presence of certain inorganic ions.
Organisms are made up of cells. Cells of different organisms have similar chemical compositions. Table 1 presents the main chemical elements found in the cells of living organisms.
Table 1. Content of chemical elements in the cell
Based on the content in the cell, three groups of elements can be distinguished. The first group includes oxygen, carbon, hydrogen and nitrogen. They account for almost 98% of the total composition of the cell. The second group includes potassium, sodium, calcium, sulfur, phosphorus, magnesium, iron, chlorine. Their content in the cell is tenths and hundredths of a percent. Elements of these two groups are classified as macronutrients(from Greek macro- big).
The remaining elements, represented in the cell by hundredths and thousandths of a percent, are included in the third group. This microelements(from Greek micro- small).
No elements unique to living nature were found in the cell. All of the listed chemical elements are also part of inanimate nature. This indicates the unity of living and inanimate nature.
A deficiency of any element can lead to illness and even death of the body, since each element plays a specific role. Macroelements of the first group form the basis of biopolymers - proteins, carbohydrates, nucleic acids, as well as lipids, without which life is impossible. Sulfur is part of some proteins, phosphorus is part of nucleic acids, iron is part of hemoglobin, and magnesium is part of chlorophyll. Calcium plays an important role in metabolism.
Some of the chemical elements contained in the cell are part of inorganic substances - mineral salts and water.
Mineral salts are found in the cell, as a rule, in the form of cations (K +, Na +, Ca 2+, Mg 2+) and anions (HPO 2-/4, H 2 PO -/4, CI -, HCO 3), the ratio of which determines the acidity of the environment, which is important for the life of cells.
(In many cells, the environment is slightly alkaline and its pH almost does not change, since a certain ratio of cations and anions is constantly maintained in it.)
Of the inorganic substances in living nature, plays a huge role water.
Without water, life is impossible. It makes up a significant mass of most cells. A lot of water is contained in the cells of the brain and human embryos: more than 80% water; in adipose tissue cells - only 40.% By old age, the water content in cells decreases. A person who has lost 20% of water dies.
The unique properties of water determine its role in the body. It is involved in thermoregulation, which is due to the high heat capacity of water - the consumption of a large amount of energy when heating. What determines the high heat capacity of water?
In a water molecule, an oxygen atom is covalently bonded to two hydrogen atoms. The water molecule is polar because the oxygen atom has a partially negative charge, and each of the two hydrogen atoms has
Partially positive charge. A hydrogen bond is formed between the oxygen atom of one water molecule and the hydrogen atom of another molecule. Hydrogen bonds provide the connection of a large number of water molecules. When water is heated, a significant part of the energy is spent on breaking hydrogen bonds, which determines its high heat capacity.
Water - good solvent. Due to their polarity, its molecules interact with positively and negatively charged ions, thereby promoting the dissolution of the substance. In relation to water, all cell substances are divided into hydrophilic and hydrophobic.
Hydrophilic(from Greek hydro- water and filleo- love) are called substances that dissolve in water. These include ionic compounds (for example, salts) and some non-ionic compounds (for example, sugars).
Hydrophobic(from Greek hydro- water and Phobos- fear) are substances that are insoluble in water. These include, for example, lipids.
Water plays an important role in the chemical reactions that occur in the cell in aqueous solutions. It dissolves metabolic products that the body does not need and thereby promotes their removal from the body. The high water content in the cell gives it elasticity. Water facilitates the movement of various substances within a cell or from cell to cell.
Bodies of living and inanimate nature consist of the same chemical elements. Living organisms contain inorganic substances - water and mineral salts. The vitally important numerous functions of water in a cell are determined by the characteristics of its molecules: their polarity, the ability to form hydrogen bonds.
INORGANIC COMPONENTS OF THE CELL
About 90 elements are found in the cells of living organisms, and about 25 of them are found in almost all cells. Based on their content in the cell, chemical elements are divided into three large groups: macroelements (99%), microelements (1%), ultramicroelements (less than 0.001%).
Macroelements include oxygen, carbon, hydrogen, phosphorus, potassium, sulfur, chlorine, calcium, magnesium, sodium, iron.
Microelements include manganese, copper, zinc, iodine, fluorine.
Ultramicroelements include silver, gold, bromine, and selenium.
| ELEMENTS | CONTENT IN THE BODY (%) | BIOLOGICAL SIGNIFICANCE |
| Macronutrients: | ||
| O.C.H.N. | 62-3 | Contains all organic matter in cells, water |
| Phosphorus R | 1,0 | They are part of nucleic acids, ATP (forms high-energy bonds), enzymes, bone tissue and tooth enamel |
| Calcium Ca +2 | 2,5 | In plants it is part of the cell membrane, in animals - in the composition of bones and teeth, activates blood clotting |
| Microelements: | 1-0,01 | |
| Sulfur S | 0,25 | Contains proteins, vitamins and enzymes |
| Potassium K+ | 0,25 | Causes the conduction of nerve impulses; activator of protein synthesis enzymes, photosynthesis processes, plant growth |
| Chlorine CI - | 0,2 | It is a component of gastric juice in the form of hydrochloric acid, activates enzymes |
| Sodium Na+ | 0,1 | Ensures the conduction of nerve impulses, maintains osmotic pressure in the cell, stimulates the synthesis of hormones |
| Magnesium Mg +2 | 0,07 | Part of the chlorophyll molecule, found in bones and teeth, activates DNA synthesis and energy metabolism |
| Iodine I - | 0,1 | Part of the thyroid hormone - thyroxine, affects metabolism |
| Iron Fe+3 | 0,01 | It is part of hemoglobin, myoglobin, the lens and cornea of the eye, an enzyme activator, and is involved in the synthesis of chlorophyll. Provides oxygen transport to tissues and organs |
| Ultramicroelements: | less than 0.01, trace amounts | |
| Copper Si +2 | Participates in the processes of hematopoiesis, photosynthesis, catalyzes intracellular oxidative processes | |
| Manganese Mn | Increases plant productivity, activates the process of photosynthesis, affects hematopoietic processes | |
| Bor V | Affects plant growth processes | |
| Fluorine F | It is part of the tooth enamel; if there is a deficiency, caries develops; if there is an excess, fluorosis develops. | |
| Substances: | ||
| N 2 0 | 60-98 | It makes up the internal environment of the body, participates in hydrolysis processes, and structures the cell. Universal solvent, catalyst, participant in chemical reactions |
ORGANIC COMPONENTS OF CELLS
| SUBSTANCES | STRUCTURE AND PROPERTIES | FUNCTIONS |
| Lipids | ||
| Esters of higher fatty acids and glycerol. The composition of phospholipids additionally includes the residue H 3 PO4. They have hydrophobic or hydrophilic-hydrophobic properties and high energy intensity | Construction- forms the bilipid layer of all membranes. Energy. Thermoregulatory. Protective. Hormonal(corticosteroids, sex hormones). Components of vitamins D, E. Source of water in the body. Reserve nutrient |
|
| Carbohydrates | ||
| Monosaccharides: glucose, fructose, ribose, deoxyribose |
Highly soluble in water | Energy |
| Disaccharides: sucrose, maltose (malt sugar) |
Soluble in water | Components DNA, RNA, ATP |
| Polysaccharides: starch, glycogen, cellulose |
Poorly soluble or insoluble in water | Spare nutrient. Construction - the shell of a plant cell |
| Squirrels | Polymers. Monomers - 20 amino acids. | Enzymes are biocatalysts. |
| I structure is the sequence of amino acids in the polypeptide chain. Bond - peptide - CO-NH- | Construction - are part of membrane structures, ribosomes. | |
| II structure - a-helix, bond - hydrogen | Motor (contractile muscle proteins). | |
| III structure - spatial configuration a-spirals (globule). Bonds - ionic, covalent, hydrophobic, hydrogen | Transport (hemoglobin). Protective (antibodies). Regulatory (hormones, insulin) | |
| The IV structure is not characteristic of all proteins. Connection of several polypeptide chains into a single superstructure. Poorly soluble in water. The action of high temperatures, concentrated acids and alkalis, heavy metal salts causes denaturation | ||
| Nucleic acids: | Biopolymers. Made up of nucleotides | |
| DNA is deoxyribonucleic acid. | Nucleotide composition: deoxyribose, nitrogenous bases - adenine, guanine, cytosine, thymine, H 3 PO 4 residue. Complementarity of nitrogenous bases A = T, G = C. Double helix. Capable of self-doubling | They form chromosomes. Storage and transmission of hereditary information, genetic code. Biosynthesis of RNA and proteins. Encodes the primary structure of a protein. Contained in the nucleus, mitochondria, plastids |
| RNA is ribonucleic acid. | Nucleotide composition: ribose, nitrogenous bases - adenine, guanine, cytosine, uracil, H 3 PO 4 residue Complementarity of nitrogenous bases A = U, G = C. One chain | |
| Messenger RNA | Transfer of information about the primary structure of the protein, participates in protein biosynthesis | |
| Ribosomal RNA | Builds the ribosome body | |
| Transfer RNA | Encodes and transports amino acids to the site of protein synthesis - ribosomes | |
| Viral RNA and DNA | Genetic apparatus of viruses | |
Enzymes.
The most important function of proteins is catalytic. Protein molecules that increase the rate of chemical reactions in a cell by several orders of magnitude are called enzymes. Not a single biochemical process in the body occurs without the participation of enzymes.
Currently, over 2000 enzymes have been discovered. Their efficiency is many times higher than the efficiency of inorganic catalysts used in production. Thus, 1 mg of iron in the catalase enzyme replaces 10 tons of inorganic iron. Catalase increases the rate of decomposition of hydrogen peroxide (H 2 O 2) by 10 11 times. The enzyme that catalyzes the reaction of carbonic acid formation (CO 2 + H 2 O = H 2 CO 3) accelerates the reaction 10 7 times.
An important property of enzymes is the specificity of their action; each enzyme catalyzes only one or a small group of similar reactions.
The substance that the enzyme acts on is called substrate. The structures of the enzyme and substrate molecules must exactly match each other. This explains the specificity of the action of enzymes. When a substrate is combined with an enzyme, the spatial structure of the enzyme changes.
The sequence of interaction between enzyme and substrate can be depicted schematically:
Substrate+Enzyme - Enzyme-substrate complex - Enzyme+Product.
The diagram shows that the substrate combines with the enzyme to form an enzyme-substrate complex. In this case, the substrate is transformed into a new substance - a product. At the final stage, the enzyme is released from the product and again interacts with another substrate molecule.
Enzymes function only at a certain temperature, concentration of substances, and acidity of the environment. Changing conditions leads to changes in the tertiary and quaternary structure of the protein molecule, and, consequently, to the suppression of enzyme activity. How does this happen? Only a certain part of the enzyme molecule, called active center. The active center contains from 3 to 12 amino acid residues and is formed as a result of bending of the polypeptide chain.
Under the influence of various factors, the structure of the enzyme molecule changes. In this case, the spatial configuration of the active center is disrupted, and the enzyme loses its activity.
Enzymes are proteins that act as biological catalysts. Thanks to enzymes, the rate of chemical reactions in cells increases by several orders of magnitude. An important property of enzymes is their specificity of action under certain conditions.
Nucleic acids.
Nucleic acids were discovered in the second half of the 19th century. Swiss biochemist F. Miescher, who isolated a substance with a high content of nitrogen and phosphorus from cell nuclei and called it “nuclein” (from lat. core- core).
Nucleic acids store hereditary information about the structure and functioning of every cell and all living beings on Earth. There are two types of nucleic acids - DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Nucleic acids, like proteins, are species specific, that is, organisms of each species have their own type of DNA. To find out the reasons for species specificity, consider the structure of nucleic acids.
Nucleic acid molecules are very long chains consisting of many hundreds and even millions of nucleotides. Any nucleic acid contains only four types of nucleotides. The functions of nucleic acid molecules depend on their structure, the nucleotides they contain, their number in the chain and the sequence of the compound in the molecule.
Each nucleotide consists of three components: a nitrogenous base, a carbohydrate and a phosphoric acid. Each DNA nucleotide contains one of four types of nitrogenous bases (adenine - A, thymine - T, guanine - G or cytosine - C), as well as deoxyribose carbon and a phosphoric acid residue.
Thus, DNA nucleotides differ only in the type of nitrogenous base.
The DNA molecule consists of a huge number of nucleotides connected in a chain in a certain sequence. Each type of DNA molecule has its own number and sequence of nucleotides.
DNA molecules are very long. For example, to write down the sequence of nucleotides in DNA molecules from one human cell (46 chromosomes) in letters would require a book of about 820,000 pages. The alternation of four types of nucleotides can form an infinite number of variants of DNA molecules. These structural features of DNA molecules allow them to store a huge amount of information about all the characteristics of organisms.
In 1953, the American biologist J. Watson and the English physicist F. Crick created a model of the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two chains, interconnected and spirally twisted. It looks like a double helix. In each chain, four types of nucleotides alternate in a specific sequence.
The nucleotide composition of DNA varies among different types of bacteria, fungi, plants, and animals. But it does not change with age and depends little on environmental changes. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule is subject to a certain rule, namely: adenine of one chain is always connected by two hydrogen bonds only with Thymine of the other chain, and guanine - by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complementing each other.
Nucleic acid molecules - DNA and RNA - are made up of nucleotides. DNA nucleotides include a nitrogenous base (A, T, G, C), the carbohydrate deoxyribose and a phosphoric acid molecule residue. The DNA molecule is a double helix, consisting of two chains connected by hydrogen bonds according to the principle of complementarity. The function of DNA is to store hereditary information.
The cells of all organisms contain molecules of ATP - adenosine triphosphoric acid. ATP is a universal cell substance, the molecule of which has energy-rich bonds. The ATP molecule is one unique nucleotide, which, like other nucleotides, consists of three components: a nitrogenous base - adenine, a carbohydrate - ribose, but instead of one it contains three residues of phosphoric acid molecules (Fig. 12). The connections indicated in the figure with an icon are rich in energy and are called macroergic. Each ATP molecule contains two high-energy bonds.
When a high-energy bond is broken and one molecule of phosphoric acid is removed with the help of enzymes, 40 kJ/mol of energy is released, and ATP is converted into ADP - adenosine diphosphoric acid. When another molecule of phosphoric acid is removed, another 40 kJ/mol is released; AMP is formed - adenosine monophosphoric acid. These reactions are reversible, that is, AMP can be converted into ADP, ADP into ATP.
ATP molecules are not only broken down, but also synthesized, so their content in the cell is relatively constant. The importance of ATP in the life of a cell is enormous. These molecules play a leading role in the energy metabolism necessary to ensure the life of the cell and the organism as a whole.
Rice. 12. Scheme of the structure of ATP.| adenine - |
An RNA molecule is usually a single chain, consisting of four types of nucleotides - A, U, G, C. Three main types of RNA are known: mRNA, rRNA, tRNA. The content of RNA molecules in a cell is not constant; they participate in protein biosynthesis. ATP is a universal energy substance of the cell, which contains energy-rich bonds. ATP plays a central role in cellular energy metabolism. RNA and ATP are found in both the nucleus and cytoplasm of the cell.
Tasks and tests on the topic "Topic 4. "Chemical composition of the cell."
- polymer, monomer;
- carbohydrate, monosaccharide, disaccharide, polysaccharide;
- lipid, fatty acid, glycerol;
- amino acid, peptide bond, protein;
- catalyst, enzyme, active site;
- nucleic acid, nucleotide.
Algorithm for solving problems.
Type 1. Self-copying of DNA.
One of the DNA chains has the following nucleotide sequence:
AGTACCGATACCGATTTACCG...
What nucleotide sequence does the second chain of the same molecule have?
To write the nucleotide sequence of the second strand of a DNA molecule, when the sequence of the first strand is known, it is enough to replace thymine with adenine, adenine with thymine, guanine with cytosine, and cytosine with guanine. Having made this replacement, we get the sequence:
TATTGGGCTATGAGCTAAAATG...
Type 2. Protein coding.
The chain of amino acids of the ribonuclease protein has the following beginning: lysine-glutamine-threonine-alanine-alanine-alanine-lysine...
What nucleotide sequence does the gene corresponding to this protein begin with?
To do this, use the genetic code table. For each amino acid, we find its code designation in the form of the corresponding triple of nucleotides and write it down. By arranging these triplets one after another in the same order as the corresponding amino acids, we obtain the formula for the structure of a section of messenger RNA. As a rule, there are several such triplets, the choice is made according to your decision (but only one of the triplets is taken). Accordingly, there may be several solutions.
ААААААААЦУГЦГГЦУГЦГАAG
What sequence of amino acids does a protein begin with if it is encoded by the following sequence of nucleotides:
ACCTTCCATGGCCGGT...
Using the principle of complementarity, we find the structure of a section of messenger RNA formed on a given segment of a DNA molecule:
UGCGGGGUACCGGCCCA...
Then we turn to the table of the genetic code and for each triple of nucleotides, starting from the first, we find and write out the corresponding amino acid:
Cysteine-glycine-tyrosine-arginine-proline-...
Ivanova T.V., Kalinova G.S., Myagkova A.N. "General Biology". Moscow, "Enlightenment", 2000
- Topic 4. "Chemical composition of the cell." §2-§7 pp. 7-21
- Topic 5. "Photosynthesis." §16-17 pp. 44-48
- Topic 6. "Cellular respiration." §12-13 pp. 34-38
- Topic 7. "Genetic information." §14-15 pp. 39-44
Test tasks on the topic
"INORGANIC SUBSTANCES OF CELLS"
Choose one correct answer from the given options:
1.
What chemical elements contained in the cell are classified as macroelements?
a) Zn, I, F, Br;
c) Ni, Cu, I, Br.
d) Au, Ag, Ra, U.
2.
What are the functions of water in a cell?
c) source of energy.
d) transmission of nerve impulses
3.
What ions make up hemoglobin?
a) Mg 2+;
4. The transmission of excitation through a nerve or muscle is explained by:
a) the difference in the concentrations of sodium and potassium ions inside and outside the cell
b) breaking of hydrogen bonds between water molecules
c) change in the concentration of hydrogen ions
d) thermal conductivity of water
5 . Of the following substances is hydrophilic:
a) starch
d) cellulose
6. The chlorophyll molecule contains ions
d) Na+
7.
At the same time it is part of bone tissue and nucleic acids:
b) phosphorus
c) calcium
8 . Children develop rickets with a deficiency of:
a) manganese and iron
b) calcium and phosphorus
c) copper and zinc
d) sulfur and nitrogen
9 . The composition of gastric juice includes:
10.
Most water is contained in cells:
a) embryo;
b) a young man;
c) an old man.
d) an adult
11.
What chemical elements contained in the cell are classified as microelements?
a) S, Na, Ca, K;
c) Ni, Cu, I, Br.
d) P, S, Cl, Na
12.
The composition of gastric juice includes
a) sulfuric acid;
b) hydrochloric acid;
c) carbonic acid.
d) phosphoric acid
13.
What are the functions of minerals in a cell?
a) transfer of hereditary information;
b) environment for chemical reactions;
c) source of energy;
d) maintaining the osmotic pressure of the cell.
14.
What ions affect blood clotting?
a) Mg 2+;
15 . Iron is included in:
c) hemoglobin
d) chlorophyll
16.
Less water is contained in cells:
a) bone tissue;
b) nervous tissue;
c) muscle tissue.
d) adipose tissue
17.
Substances that are poorly soluble in water are called:
a) hydrophilic;
b) hydrophobic;
c) amphiphilic.
d) amphoteric
18.
Buffering in the cell is provided by ions:
a) Na +, K +;
b) SO 4 2-, Cl -;
c) HCO 3 -, CO 3 2-.
d) Mg 2+; Fe 2+
19.
Water is the basis of life, because... she:
a) can be in three states (liquid, solid and gaseous);
b) is a solvent that ensures both the influx of substances into the cell and the removal of metabolic products from it;
c) cools the surface during evaporation.
d) has the property of thermal conductivity
20 . Of the following substances is hydrophobic:
d) potassium permanganate
Sample answers