The role of carbohydrates in the plant cell. The role of carbohydrates in the body

Introduction.

Structure, properties and functions of proteins.
Protein metabolism.
Carbohydrates.
Structure, properties and functions of carbohydrates.
The exchange of carbohydrates.
Structure, properties and functions of fats.

10) Metabolism of fats.

Bibliography

INTRODUCTION

Normal activity of the body is possible with a continuous supply of food. The fats, proteins, carbohydrates, mineral salts, water and vitamins that are part of the food are necessary for the life processes of the body.

Nutrients are both a source of energy that covers the expenses of the body, and a building material that is used in the process of growth of the body and the reproduction of new cells that replace dying ones. But nutrients in the form in which they are eaten cannot be absorbed and used by the body. Only water, mineral salts and vitamins are absorbed and assimilated in the form in which they come.

Nutrients are proteins, fats and carbohydrates. These substances are essential components of food. In the digestive tract, proteins, fats and carbohydrates are subjected to both physical influences (crushed and ground) and chemical changes that occur under the influence of special substances - enzymes contained in the juices of the digestive glands. Under the influence of digestive juices, nutrients are broken down into simpler ones, which are absorbed and absorbed by the body.

PROTEINS

STRUCTURE, PROPERTIES AND FUNCTIONS

"In all plants and animals there is a certain substance, which is without a doubt the most important of all known substances of living nature and without which life would be impossible on our planet. I named this substance - protein." So wrote in 1838 the Dutch biochemist Gerard Mulder, who first discovered the existence of protein bodies in nature and formulated his protein theory. The word "protein" (protein) comes from the Greek word "proteios", which means "in first place". Indeed, all life on earth contains proteins. They make up about 50% of the dry body weight of all organisms. In viruses, the protein content ranges from 45 to 95%.

Proteins are one of the four basic organic substances of living matter (proteins, nucleic acids, carbohydrates, fats), but in terms of their significance and biological functions, they occupy a special place in it. About 30% of all proteins in the human body are found in muscles, about 20% in bones and tendons, and about 10% in skin. But the most important proteins of all organisms are enzymes, which, although present in their body and in every cell of the body in small quantities, nevertheless control a number of chemical reactions essential to life. All processes occurring in the body: digestion of food, oxidative reactions, activity of endocrine glands, muscle activity and brain function are regulated by enzymes. The variety of enzymes in the body of organisms is enormous. Even in a small bacterium there are many hundreds of them.

Proteins, or, as they are otherwise called, proteins, have a very complex structure and are the most complex of nutrients. Proteins are an essential part of all living cells. Proteins include: carbon, hydrogen, oxygen, nitrogen, sulfur and sometimes phosphorus. The most characteristic of a protein is the presence of nitrogen in its molecule. Other nutrients do not contain nitrogen. Therefore, protein is called a nitrogen-containing substance.

The main nitrogen-containing substances that make up proteins are amino acids. The number of amino acids is small - only 28 of them are known. All the huge variety of proteins contained in nature is a different combination of known amino acids. The properties and qualities of proteins depend on their combination.

When two or more amino acids are combined, a more complex compound is formed - polypeptide. Polypeptides, when combined, form even more complex and large particles and, as a result, a complex protein molecule.

When proteins are broken down into simpler compounds in the digestive tract or in experiments, they are broken down into polypeptides and finally into amino acids through a series of intermediate steps (albumosis and peptones). Amino acids, unlike proteins, are easily absorbed and absorbed by the body. They are used by the body to form its own specific protein. If, due to the excess intake of amino acids, their breakdown in the tissues continues, then they are oxidized to carbon dioxide and water.

Most proteins are soluble in water. Due to their large size, protein molecules hardly pass through the pores of animal or plant membranes. When heated, aqueous solutions of proteins coagulate. There are proteins (such as gelatin) that dissolve in water only when heated.

When swallowed, food first enters the mouth, and then through the esophagus to the stomach. Pure gastric juice is colorless and acidic. The acid reaction depends on the presence of hydrochloric acid, the concentration of which is 0.5%.

Gastric juice has the ability to digest food, which is associated with the presence of enzymes in it. It contains pepsin, an enzyme that breaks down protein. Under the influence of pepsin, proteins are broken down into peptones and albumoses. The glands of the stomach produce pepsin in an inactive form, it becomes active when exposed to hydrochloric acid. Pepsin acts only in an acidic environment and becomes negative when it enters an alkaline environment.

Food, having entered the stomach, lingers in it for a more or less long time - from 3 to 10 hours. The length of stay of food in the stomach depends on its nature and physical condition - it is liquid or solid. Water leaves the stomach immediately upon entry. Foods containing more proteins stay in the stomach longer than carbohydrate foods; fatty foods remain in the stomach longer. The movement of food occurs due to the contraction of the stomach, which contributes to the transition to the pyloric part, and then to the duodenum of the already significantly digested food slurry.

Food slurry that enters the duodenum undergoes further digestion. Here, the juice of the intestinal glands, with which the intestinal mucosa is dotted, as well as pancreatic juice and bile, is poured onto the food gruel. Under the influence of these juices, nutrients - proteins, fats and carbohydrates - are further broken down and brought to a state where they can be absorbed into the blood and lymph.

Pancreatic juice is colorless and alkaline. It contains enzymes that break down proteins, carbohydrates and fats.

One of the main enzymes is trypsin, in the pancreatic juice in an inactive state in the form of trypsinogen. Trypsinogen cannot break down proteins if it is not transferred to an active state, i.e. into trypsin. Trypsinogen is converted to trypsin upon contact with intestinal juice under the influence of a substance present in the intestinal juice. enterokinase. Enterokinase is produced in the intestinal mucosa. In the duodenum, the action of pepsin ceases, since pepsin acts only in an acidic environment. Further digestion of proteins continues under the influence of trypsin.

Trypsin is very active in an alkaline environment. Its action continues in an acidic environment, but the activity decreases. Trypsin acts on proteins and breaks them down to amino acids; it also breaks down peptones and albumoses formed in the stomach into amino acids.

In the small intestines, the processing of nutrients, which began in the stomach and duodenum, ends. In the stomach and duodenum, proteins, fats and carbohydrates are broken down almost completely, only part of them remains undigested. In the small intestines, under the influence of intestinal juice, the final breakdown of all nutrients and the absorption of cleavage products occur. The cleavage products enter the blood. This happens through capillaries, each of which approaches a villus located on the wall of the small intestine.

PROTEIN METABOLISM

After the breakdown of proteins in the digestive tract, the resulting amino acids are absorbed into the blood. A small amount of polypeptides, compounds consisting of several amino acids, is also absorbed into the blood. From amino acids, the cells of our body synthesize protein, and the protein that is formed in the cells of the human body is different from the consumed protein and is characteristic of the human body.

The formation of a new protein in the body of man and animals goes on uninterruptedly, since throughout life, instead of dying cells of the blood, skin, mucous membrane, intestines, etc., new, young cells are created. In order for the cells of the body to synthesize protein, it is necessary that the proteins enter the digestive canal with food, where they undergo splitting into amino acids, and protein will be formed from the absorbed amino acids.

If, bypassing the digestive tract, introduce the protein directly into the blood, then not only can it not be used by the human body, it causes a number of serious complications. The body responds to such an introduction of protein with a sharp increase in temperature and some other phenomena. With the repeated introduction of protein in 15-20 days, even death can occur with respiratory paralysis, a sharp violation of cardiac activity and general convulsions.

Proteins cannot be replaced by any other food substances, since protein synthesis in the body is possible only from amino acids.

In order for the synthesis of its inherent protein to occur in the body, the intake of all or the most important amino acids is necessary.

Of the known amino acids, not all have the same value for the body. Among them are amino acids that can be replaced by others or synthesized in the body from other amino acids; along with this, there are essential amino acids, in the absence of which, or even one of them, protein metabolism in the body is disturbed.

Proteins do not always contain all the amino acids: some proteins contain a larger amount of amino acids needed by the body, while others contain a small amount. Different proteins contain different amino acids and in different ratios.

Proteins, which include all the amino acids necessary for the body, are called complete; proteins that do not contain all the necessary amino acids are incomplete proteins.

For a person, the intake of complete proteins is important, since the body can freely synthesize its own specific proteins from them. However, a complete protein can be replaced by two or three incomplete proteins, which, complementing each other, give in total all the necessary amino acids. Therefore, for the normal functioning of the body, it is necessary that the food contains complete proteins or a set of incomplete proteins, which are equivalent in amino acid content to complete proteins.

The intake of complete proteins with food is extremely important for a growing organism, since in the child's body not only the restoration of dying cells occurs, as in adults, but new cells are also created in large numbers.

Ordinary mixed food contains a variety of proteins, which together provide the body's need for amino acids. Not only the biological value of proteins coming from food is important, but also their quantity. With an insufficient amount of protein, the normal growth of the body is suspended or delayed, since the need for protein is not covered due to its insufficient intake.

Complete proteins are mainly proteins of animal origin, with the exception of gelatin, which is classified as incomplete proteins. Incomplete proteins are predominantly of vegetable origin. However, some plants (potatoes, legumes, etc.) contain complete proteins. Of animal proteins, the proteins of meat, eggs, milk, etc. are especially valuable for the body.

CARBOHYDRATES

STRUCTURE, PROPERTIES AND FUNCTIONS

Carbohydrates or saccharides are one of the main groups of organic compounds in the body. They are the primary products of photosynthesis and the initial products of the biosynthesis of other substances in plants (organic acids, amino acids), and are also found in the cells of all other living organisms. In an animal cell, the content of carbohydrates ranges from 1-2%, in a plant cell it can reach in some cases 85-90% of the dry matter mass.

Carbohydrates are made up of carbon, hydrogen and oxygen, and most carbohydrates contain hydrogen and oxygen in the same ratio as in water (hence their name - carbohydrates). Such, for example, are glucose C6H12O6 or sucrose C12H22O11. Other elements may also be included in the composition of carbohydrate derivatives. All carbohydrates are divided into simple (monosaccharides) and complex (polysaccharides).

Among monosaccharides, according to the number of carbon atoms, trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C) and heptoses (7C) are distinguished. Monosaccharides with five or more carbon atoms, when dissolved in water, can acquire a ring structure. In nature, the most common are pentoses (ribose, deoxyribose, ribulose) and hexoses (glucose, fructose, galactose). Ribose and deoxyribose play an important role as constituents of nucleic acids and ATP. Glucose in the cell serves as a universal source of energy. With the transformation of monosaccharides, not only providing the cell with energy is associated, but also the biosynthesis of many other organic substances, as well as the neutralization and removal from the body of toxic substances that penetrate from the outside or are formed in the process of metabolism, for example, during the breakdown of proteins.

Di- and polysaccharides are formed by combining two or more monosaccharides, such as glucose, galactose, manose, arabinose, or xylose. So, connecting with each other with the release of a water molecule, two molecules of monosaccharides form a disaccharide molecule. Typical representatives of this group of substances are sucrose (cane sugar), maltase (malt sugar), lactose (milk sugar). Disaccharides are similar in properties to monosaccharides. For example, both of them are highly soluble in water and have a sweet taste. Polysaccharides include starch, glycogen, cellulose, chitin, callose, etc.

The main role of carbohydrates is associated with their energy function. During their enzymatic cleavage and oxidation, energy is released, which is used by the cell. Polysaccharides play a major role spare products and easily mobilized energy sources (e.g. starch and glycogen), and are also used as building material(cellulose, chitin). Polysaccharides are convenient as reserve substances for a number of reasons: being insoluble in water, they do not have either an osmotic or chemical effect on the cell, which is very important for long-term storage in a living cell: the solid, dehydrated state of polysaccharides increases the useful mass of reserve products due to savings in volume. At the same time, the probability of consumption of these products by pathogenic bacteria and other microorganisms, which, as you know, cannot swallow food, but absorb substances from the entire surface of the body, is significantly reduced. And finally, if necessary, storage polysaccharides can be easily converted into simple sugars by hydrolysis.

CARBOHYDRATE METABOLISM

Carbohydrates, as mentioned above, play a very important role in the body, being the main source of energy. Carbohydrates enter our body in the form of complex polysaccharides - starch, disaccharides and monosaccharides. Most carbohydrates come in the form of starch. After being broken down to glucose, carbohydrates are absorbed and, through a series of intermediate reactions, break down into carbon dioxide and water. These transformations of carbohydrates and the final oxidation are accompanied by the release of energy, which is used by the body.

The breakdown of complex carbohydrates - starch and malt sugar, begins already in the oral cavity, where, under the influence of ptyalin and maltase, starch is broken down to glucose. In the small intestine, all carbohydrates are broken down into monosaccharides.

Water carbon is absorbed mainly in the form of glucose and only partly in the form of other monosaccharides (galactose, fructose). Their absorption begins already in the upper intestine. In the lower sections of the small intestines, almost no carbohydrates are contained in the food gruel. Carbohydrates are absorbed through the villi of the mucous membrane, to which the capillaries fit, into the blood, and with the blood flowing from the small intestine, enter the portal vein. Portal vein blood passes through the liver. If the concentration of sugar in a person's blood is 0.1%, then carbohydrates pass through the liver and enter the general circulation.

The amount of sugar in the blood is constantly maintained at a certain level. In plasma, the sugar content averages 0.1%. The liver plays an important role in maintaining a constant blood sugar level. With an abundant intake of sugar in the body, its excess is deposited in the liver and re-enters the blood when the blood sugar level drops. Carbohydrates are stored in the liver in the form of glycogen.

When eating starch, the blood sugar level does not undergo noticeable changes, since the breakdown of starch in the digestive tract lasts a long time and the monosaccharides formed during this are absorbed slowly. With the intake of a significant amount (150-200g) of regular sugar or glucose, the blood sugar level rises sharply.

This increase in blood sugar is called food or alimentary hyperglycemia. Excess sugar is excreted by the kidneys, and glucose appears in the urine.

Removal of sugar by the kidneys begins when the blood sugar level is 0.15-0.18%. Such alimentary hyperglycemia usually occurs after consuming a large amount of sugar and soon passes without causing any disturbances in the body's activity.

However, when the intrasecretory activity of the pancreas is disturbed, a disease occurs, known as sugar disease or diabetes mellitus. With this disease, blood sugar levels rise, the liver loses the ability to noticeably retain sugar, and an increased excretion of sugar in the urine begins.

Glycogen is deposited not only in the liver. A significant amount of it is also found in the muscles, where it is consumed in the chain of chemical reactions that occur in the muscles during contraction.

During physical work, the consumption of carbohydrates increases, and their amount in the blood increases. The increased demand for glucose is satisfied both by the breakdown of liver glycogen into glucose and the latter's entry into the blood, and by the glycogen contained in the muscles.

The value of glucose for the body is not limited to its role as an energy source. This monosaccharide is part of the protoplasm of cells and, therefore, is necessary for the formation of new cells, especially during the growth period. Of great importance is glucose in the activity of the central nervous system. It is enough that the concentration of sugar in the blood drops to 0.04%, as convulsions begin, consciousness is lost, etc.; in other words, with a decrease in blood sugar, the activity of the central nervous system is primarily disrupted. It is enough for such a patient to inject glucose into the blood or give ordinary sugar to eat, and all disorders disappear. A sharper and more prolonged decrease in blood sugar levels - glycoglycemia, can lead to severe disruption of the body's activity and lead to death.

With a small intake of carbohydrates with food, they are formed from proteins and fats. Thus, it is not possible to completely deprive the body of carbohydrates, since they are also formed from other nutrients.

FATS

STRUCTURE, PROPERTIES AND FUNCTIONS

Fats are made up of carbon, hydrogen and oxygen. Fat has a complex structure; its constituent parts are glycerol (С3Н8О3) and fatty acids, when combined, fat molecules are formed. The most common are three fatty acids: oleic (C18H34O2), palmitic (C16H32O2) and stearic (C18H36O2). The combination of these fatty acids when combined with glycerol depends on the formation of one or another fat. When glycerol is combined with oleic acid, a liquid fat is formed, for example, vegetable oil. Palmitic acid forms a harder fat, is part of butter and is the main constituent of human fat. Stearic acid is part of even harder fats, such as lard. In order for the human body to synthesize a specific fat, it is necessary to supply all three fatty acids.

During digestion, fat is broken down into its component parts - glycerol and fatty acids. Fatty acids are neutralized by alkalis, resulting in the formation of their salts - soaps. Soaps dissolve in water and are easily absorbed.

Fats are an integral part of protoplasm and are part of all organs, tissues and cells of the human body. In addition, fats are a rich source of energy.

The breakdown of fats begins in the stomach. Gastric juice contains a substance called lipase. Lipase breaks down fats into fatty acids and glycerol. Glycerin dissolves in water and is easily absorbed, while fatty acids do not dissolve in water. Bile promotes their dissolution and absorption. However, only fat is broken down in the stomach, broken down into small particles, such as milk fat. Under the influence of bile, the action of lipase is enhanced by 15-20 times. Bile helps to break down fat into tiny particles.

From the stomach, food enters the duodenum. Here, the juice of the intestinal glands is poured onto it, as well as the juice of the pancreas and bile. Under the influence of these juices, fats are further broken down and brought to a state where they can be absorbed into the blood and lymph. Then, through the digestive tract, the food slurry enters the small intestine. There, under the influence of intestinal juice, the final splitting and absorption takes place.

Fat is broken down into glycerol and fatty acids by the enzyme lipase. Glycerin is soluble and easily absorbed, while fatty acids are insoluble in the intestinal contents and cannot be absorbed.

Fatty acids enter into combination with alkalis and bile acids and form soaps, which dissolve easily and therefore pass through the intestinal wall without difficulty. Unlike the breakdown products of carbohydrates and proteins, the breakdown products of fats are absorbed not into the blood, but into the lymph, and glycerin and soaps, passing through the cells of the intestinal mucosa, recombine and form fat; therefore, already in the lymphatic vessel of the villi are droplets of newly formed fat, and not glycerol and fatty acids.

FAT METABOLISM

Fats, like carbohydrates, are primarily an energy material and are used by the body as an energy source.

When 1 g of fat is oxidized, the amount of energy released is more than two times greater than when the same amount of carbon or protein is oxidized.

In the digestive organs, fats are broken down into glycerol and fatty acids. Glycerol is absorbed easily, and fatty acids only after saponification.

When passing through the cells of the intestinal mucosa, fat is again synthesized from glycerol and fatty acids, which enters the lymph. The resulting fat is different from the consumed. The organism synthesizes the fat peculiar to the given organism. So, if a person consumes different fats containing oleic, palmitic stearic fatty acids, then his body synthesizes fat specific to a person. However, if only one fatty acid, for example, oleic acid, is contained in human food, if it prevails, then the resulting fat will differ from human fat and approach more liquid fats. When eating mainly mutton fat, the fat will be more solid. Fat by its nature differs not only in different animals, but also in different organs of the same animal.

Fat is used by the body not only as a rich source of energy, it is part of the cells. Fat is an obligatory component of protoplasm, nucleus and shell. The rest of the fat that has entered the body after covering its needs is deposited in the reserve in the form of fat drops.

Fat is deposited mainly in the subcutaneous tissue, omentum, around the kidneys, forming a renal capsule, as well as in other internal organs and in some other parts of the body. A significant amount of spare fat is found in the liver and muscles. Reserve fat is primarily a source of energy, which is mobilized when energy expenditure exceeds its intake. In such cases, the fat is oxidized to the end products of decomposition.

In addition to energy value, spare fat plays another role in the body; for example, subcutaneous fat prevents increased heat transfer, perirenal fat protects the kidney from bruises, etc. Quite a significant amount of fat can be stored in the body. In humans, it makes up an average of 10-20% of the body weight. In obesity, when metabolic processes in the body are disturbed, the amount of stored fat reaches 50% of a person's weight.

The amount of deposited fat depends on a number of conditions: gender, age, working conditions, health status, etc. With a sedentary nature of work, fat deposition occurs more vigorously, so the question of the composition and amount of food for people leading a sedentary lifestyle is very important.

Fat is synthesized by the body not only from incoming fat, but also from proteins and carbohydrates. With the complete exclusion of fat from food, it is still formed and in a fairly significant amount can be deposited in the body. Carbohydrates are the main source of fat in the body.

BIBLIOGRAPHY

1. V.I. Towarnicki: Molecules and viruses;

2. A.A. Markosyan: Physiology;

3. N.P. Dubinin: Ginetics and Man;

4. N.A. Lemeza: Biology in exam questions and answers.

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The role of carbohydrates in the cell

1. Cage 3
2. Composition of the cell 3
3. Carbohydrates 5
4. Functions of carbohydrates 7
5. The role of carbohydrates in the cell 7
Bibliography 10
1. Cage
Modern cell theory consists of the following generalizations.
The cell is the elementary particle of life. Manifestation of life is possible only at a level not lower than the cellular one.
The cells of all living beings have a single structural plan. It includes the cytoplasm with various organelles and a membrane. The functional basis of any cell is proteins and nucleic acids.
The cell comes only from the cell (R. Virchow, 1858) as a result of division.
The cells of multicellular organisms differ in the details of the structure, which is caused by the performance of various functions by them. Cells that have a common origin, structure and perform the same functions in the body form a tissue (nerve, muscle, integumentary). Tissues form various organs.
2. Composition of the cell
The composition of any cell includes more than 60 elements of the periodic table of Mendeleev. According to the frequency of occurrence, elements can be divided into three groups:
Main elements. These are carbon (C), hydrogen (H), nitrogen (N), oxygen (O). Their content in the cell exceeds 97%. They are part of all organic substances (proteins, fats, carbohydrates, nucleic acids) and form their basis.
Macronutrients. These include iron (Fe), sulfur (S), calcium (Ca), potassium (K), sodium (Na), phosphorus (P), chlorine (Cl). Macronutrients account for about 2%. They are part of many organic and inorganic substances.
Microelements. They have the greatest diversity (there are more than 50 of them), but in a cell, even taken all together, they do not exceed 1%. Trace elements in extremely small quantities are part of many enzymes, hormones or specific tissues, but determine their properties. So, fluorine (F), is part of the tooth enamel, strengthening it.
Iodine (I) is involved in the structure of the thyroid hormone thyroxin, magnesium (Mg) is part of the plant cell chlorophyll, copper (Cu) and selenium (Se) are found in enzymes that protect cells from mutations, zinc (Zn) is associated with memory processes.
All elements of the cell are part of various molecules, form substances that are divided into two classes: inorganic and organic.
The organic substances of the cell are represented by various biochemical polymers, that is, such molecules that consist of numerous repetitions of simpler sections (monomers) similar in structure. The organic components of a cell are carbohydrates, fats and fat-like substances, proteins and amino acids, nucleic acids and nucleic bases.
Carbohydrates include organic substances having the general chemical formula C n (H 2 O) n . By structure, carbohydrates are divided into monosaccharides, oligosaccharides and polysaccharides. Monosugars are molecules in the form of a single ring, usually containing five or six carbon atoms. Five-carbon sugars - ribose, deoxyribose. Six-carbon sugars - glucose, fructose, galactose. Oligosugar is the result of combining a small number of monosaccharides (disugar, trisugar, etc.), the most common are, for example, cane (beet) sugar - sucrose, consisting of two molecules of glucose and fructose; malt sugar - maltose formed by two molecules of glucose; milk sugar - lactose, is formed by a galactose molecule and a glucose molecule.
Polysaccharides - starch, glycogen, cellulose, consist of a huge amount of monosaccharides linked together in more or less branched chains.
3. Carbohydrates
Carbohydrates are organic substances with the general formula Cn(H2O)m.
In an animal cell, carbohydrates are found in amounts not exceeding 5%. Plant cells are the richest in carbohydrates, where their content reaches up to 90% of dry mass (potatoes, seeds, etc.)
Carbohydrates are divided into simple (monosaccharides and disaccharides) and complex (polysaccharides).
Monosaccharides are substances such as glucose, pentose, fructose, ribose. disaccharides - sugar, sucrose (consists of glucose and fructose.

Polysaccharides are made up of many monosaccharides. Monomers of such polysaccharides as starch, glycogen, cellulose is glucose.
Carbohydrates play the role of the main source of energy in the cell. in the process of oxidation, 1 g of carbohydrates releases 17.6 kJ. Starch in plants and glycogen in animals are deposited in cells and serve as an energy reserve.
Carbohydrates are organic compounds, which include hydrogen (H), carbon (C) and oxygen (O), and the number of hydrogen atoms in most cases is twice the number of oxygen atoms. The general formula for carbohydrates is Cn(H2O)n, where n is at least three. Carbohydrates are formed from water (H2O) and carbon dioxide (CO2) during photosynthesis occurring in the chloroplasts of green plants (in bacteria during bacterial photosynthesis or chemosynthesis). Usually, a cell of animal organisms contains about 1% carbohydrates (up to 5% in liver cells), and up to 90% in plant cells (in potato tubers).
All carbohydrates are divided into 3 groups:
Monosaccharides often contain five (pentoses) or six (hexoses) carbon atoms, the same amount of oxygen and twice as much hydrogen (for example, glucose - C6H12O6). Pentoses (ribose and deoxyribose) are part of nucleic acids and ATP. Hexoses (fructose and glucose) are constantly present in the cells of plant fruits, giving them a sweet taste. Glucose is found in the blood and serves as an energy source for animal cells and tissues;
Disaccharides combine two monosaccharides in one molecule. Dietary sugar (sucrose) consists of glucose and fructose molecules, milk sugar (lactose) includes glucose and galactose.
All mono- and disaccharides are highly soluble in water and have a sweet taste.
Polysaccharides (starch, fiber, glycogen, chitin) are formed by tens and hundreds of monomeric units, which are glucose molecules. Polysaccharides are practically insoluble in water and do not have a sweet taste. The main polysaccharides - starch (in plant cells) and glycogen (in animal cells) are deposited in the form of inclusions and serve as reserve energy substances.
4. Functions of carbohydrates
Carbohydrates perform two main functions: energy and construction. For example, cellulose forms the walls of plant cells (fiber), chitin is the main structural component of the external skeleton of arthropods.
Carbohydrates perform the following functions:
- they are a source of energy (the breakdown of 1 g of glucose releases 17.6 kJ of energy);
- perform a building (structural) function (cellulose shell in plant cells, chitin in the skeleton of insects and in the cell wall of fungi);
- store nutrients (starch in plant cells, glycogen in animals);
- are components of DNA, RNA and ATP.
5. The role of carbohydrates in the cell
Energy. Mono - and oligosugars are an important source of energy for any cell. Splitting, they release energy, which is stored in the form of ATP molecules, which are used in many life processes of the cell and the whole organism. The end products of the breakdown of all carbohydrates are carbon dioxide and water.
Spare. Mono- and oligosaccharides, due to their solubility, are quickly absorbed by the cell, easily migrate throughout the body, and therefore are unsuitable for long-term storage. The role of the energy reserve is played by huge water-insoluble molecules of polysaccharides. In plants, for example, it is starch, while in animals and fungi it is glycogen. To use these reserves, the body must first convert the polysugar into a monosugar.
Construction. The vast majority of plant cells have dense walls made of cellulose, which provides plants with strength, elasticity and protection against large moisture loss.
Structural. Monosugars can combine with fats, proteins and other substances. For example, ribose is part of all RNA molecules, and deoxyribose is part of DNA.
Sources of carbohydrates in the diet are mainly products of plant origin - bread, cereals, potatoes, vegetables, fruits, berries. Of the products of animal origin, carbohydrates are found in milk (milk sugar). Food products contain various carbohydrates. Cereals, potatoes contain starch - a complex substance (complex carbohydrate), insoluble in water, but split under the action of digestive juices into simpler sugars. Fruits, berries and some vegetables contain carbohydrates in the form of various simpler sugars - fruit sugar, beet sugar, cane sugar, grape sugar (glucose), etc. These substances are soluble in water and are well absorbed in the body. Water-soluble sugars are rapidly absorbed into the blood. It is advisable not to introduce all carbohydrates in the form of sugars, but to introduce the bulk of them in the form of starch, which is rich, for example, in potatoes. This contributes to the gradual delivery of sugar to the tissues. Directly in the form of sugar, it is recommended to introduce only 20-25% of the total amount of carbohydrates contained in the daily diet. This number also includes sugar contained in sweets, confectionery, fruits and berries.
If carbohydrates are supplied with food in sufficient quantities, they are deposited mainly in the liver and muscles in the form of a special animal starch - glycogen. In the future, the store of glycogen is broken down in the body to glucose and, entering the blood and other tissues, are used for the needs of the body. With excess nutrition, carbohydrates are converted into fat in the body. Carbohydrates usually include fiber (the shell of plant cells), which is little used by the human body, but is necessary for proper digestion.

Bibliography

1. Chemistry, trans. from English, 2nd ed., M., 1956; Chemistry of carbohydrates, M., 1967

2. Stepanenko B.N., Carbohydrates. Advances in the study of the structure and metabolism, M., 1968

4. Alabin V. G., Skrezhko A. D. Nutrition and health. - Minsk, 1994

5. Sotnik Zh.G., Zarichanskaya L.A. Proteins, fats and carbohydrates. - M., Prior, 2000

Modern methods of cell research

Electron microscopy.. physicists proposed to use a beam of electrons instead of a beam of light.. a transmission electron microscope..

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Enzymes
Enzymes are specific proteins that are present in all living organisms. They play the role of biological catalysts. Enzymes can be simple proteins or complex

The most important groups of enzymes
Number and name of classes Catalyzed reactions Examples 1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomer

Nucleic acids
Nucleic acids were discovered in 1869 by the Swiss chemist Miescher. There are two types of nucleic acids: DNA (deoxyribonucleic acid). RNA (ribonucleic

DNA replication
The genetic material must be capable of accurately reproducing itself at each cell division. Each DNA strand can serve as a template for the synthesis of a polypeptide chain. Such a replay mechanism

Biological membranes, their structure, properties and functions. plasma membrane
The plasma membrane, or plasmalemma, is the most permanent, basic, universal membrane for all cells. It is the thinnest (about 10 nm) film covering the

plant cell wall
The cell wall is one of the most important components of plant cells, fungi, plants have. The cell wall performs the following functions: Provides mechanical strength

Cytoplasm: hyaloplasm, cytoskeleton
The living content of eukaryotic cells is composed of the nucleus and cytoplasm, which together form protoplasm. The composition of the cytoplasm includes the main aqueous substance and the organelles in it.

Cell organelles, their structure and functions
Plastids are autonomous plant cell organelles. There are the following varieties of plastids: Proplastids Leucoplasts Etioplasts Chloropl

carbohydrates substances are called with the general formula C n (H 2 O) m, where n and m can have different values. The name "carbohydrates" reflects the fact that hydrogen and oxygen are present in the molecules of these substances in the same ratio as in the water molecule. In addition to carbon, hydrogen and oxygen, carbohydrate derivatives may contain other elements, such as nitrogen.

Carbohydrates are one of the main groups of organic substances of cells. They are the primary products of photosynthesis and the initial products of the biosynthesis of other organic substances in plants (organic acids, alcohols, amino acids, etc.), and are also found in the cells of all other organisms. In an animal cell, the content of carbohydrates is in the range of 1-2%, in plant cells it can reach in some cases 85-90% of the dry matter mass.

There are three groups of carbohydrates:

monosaccharides or simple sugars;
oligosaccharides - compounds consisting of 2-10 consecutively connected molecules of simple sugars (for example, disaccharides, trisaccharides, etc.).
polysaccharides consist of more than 10 molecules of simple sugars or their derivatives (starch, glycogen, cellulose, chitin).

Monosaccharides (simple sugars)

Depending on the length of the carbon skeleton (the number of carbon atoms), monosaccharides are divided into trioses (C 3), tetroses (C 4), pentoses (C 5), hexoses (C 6), heptoses (C 7).

Monosaccharide molecules are either aldehyde alcohols (aldoses) or keto alcohols (ketoses). The chemical properties of these substances are determined primarily by the aldehyde or ketone groups that make up their molecules.

Monosaccharides are highly soluble in water, sweet in taste.

When dissolved in water, monosaccharides, starting with pentoses, acquire a ring shape.

The cyclic structures of pentoses and hexoses are their usual forms: at any given moment, only a small fraction of the molecules exist in the form of an "open chain". The composition of oligo- and polysaccharides also includes cyclic forms of monosaccharides.

In addition to sugars, in which all carbon atoms are bonded to oxygen atoms, there are partially reduced sugars, the most important of which is deoxyribose.

Oligosaccharides

Upon hydrolysis, oligosaccharides form several molecules of simple sugars. In oligosaccharides, simple sugar molecules are connected by so-called glycosidic bonds, connecting the carbon atom of one molecule through oxygen to the carbon atom of another molecule.

The most important oligosaccharides are maltose (malt sugar), lactose (milk sugar) and sucrose (cane or beet sugar). These sugars are also called disaccharides. By their properties, disaccharides are blocks to monosaccharides. They dissolve well in water and have a sweet taste.

Polysaccharides

These are high-molecular (up to 10,000,000 Da) polymeric biomolecules consisting of a large number of monomers - simple sugars and their derivatives.

Polysaccharides may be composed of monosaccharides of the same or different types. In the first case, they are called homopolysaccharides (starch, cellulose, chitin, etc.), in the second - heteropolysaccharides (heparin). All polysaccharides are insoluble in water and do not have a sweet taste. Some of them are able to swell and mucus.

The most important polysaccharides are as follows.

Cellulose- a linear polysaccharide consisting of several straight parallel chains interconnected by hydrogen bonds. Each chain is formed by β-D-glucose residues. This structure prevents the penetration of water, is very tear-resistant, which ensures the stability of plant cell membranes, which contain 26-40% cellulose.

Cellulose serves as food for many animals, bacteria and fungi. However, most animals, including humans, cannot digest cellulose because their gastrointestinal tract lacks the enzyme cellulase, which breaks down cellulose into glucose. At the same time, cellulose fibers play an important role in nutrition, as they give bulk and coarse texture to food, stimulate intestinal motility.

starch and glycogen. These polysaccharides are the main forms of glucose storage in plants (starch), animals, humans and fungi (glycogen). When they are hydrolyzed, glucose is formed in organisms, which is necessary for vital processes.

Chitin formed by molecules of β-glucose, in which the alcohol group at the second carbon atom is replaced by a nitrogen-containing group NHCOCH 3 . Its long parallel chains, like the chains of cellulose, are bundled.

Chitin is the main structural element of the integument of arthropods and the cell walls of fungi.

Functions of carbohydrates

Energy. Glucose is the main source of energy released in the cells of living organisms during cellular respiration (1 g of carbohydrates releases 17.6 kJ of energy during oxidation).

Structural. Cellulose is part of the cell membranes of plants; chitin is a structural component of the integument of arthropods and the cell walls of fungi.

Some oligosaccharides are part of the cytoplasmic membrane of the cell (in the form of glycoproteins and glycolipids) and form a glycocalyx.

metabolic. Pentoses are involved in the synthesis of nucleotides (ribose is part of RNA nucleotides, deoxyribose is part of DNA nucleotides), some coenzymes (for example, NAD, NADP, coenzyme A, FAD), AMP; take part in photosynthesis (ribulose diphosphate is an acceptor of CO 2 in the dark phase of photosynthesis).

Pentoses and hexoses are involved in the synthesis of polysaccharides; glucose is especially important in this role.

1. Structural (construction). Carbohydrates are part of many elements of living organisms, for example, the cell wall of a plant cell, the glycocalyx of the human intestinal epithelium.

2. Signal. Carbohydrate-protein complexes (glycoproteins) form receptors (see the signaling function of proteins).

3. Protective. Connective tissue glycoproteins perform the function of chemical protection, resist hydrolytic enzymes.

4. Energy. With complete oxidation of 1 g of carbohydrates, 4.1 kcal or 17.2 kJ of energy is released.

This function is the last in the list, but the main one in value. Carbohydrates give a person more than 60% of energy.

Cell energy.

In chemical reactions, when bonds are formed between simple molecules, energy is consumed, and when broken, energy is released.

In the process of photosynthesis in green plants, the energy of sunlight is converted into the energy of chemical bonds that occur between carbon dioxide and water molecules. A glucose molecule is formed: CO 2 + H 2 O + Q (energy) \u003d C 6 H 12 O 6.

Glucose is the main source of energy for humans and most animals.

The process of assimilation of this energy is called "oxidative phosphorylation". The energy (Q) released during oxidation is immediately used for the phosphorylation of adenosine diphosphoric acid (ADP):

ADP+P+Q (energy)=ATP

It turns out the "universal energy currency" of the cell adenosine triphosphoric acid (ATP). It can be used at any time for any work useful to the body or for warming.

ATP®ADP+P+Q (energy)

The process of glucose oxidation takes place in 2 stages.

1. Anaerobic (oxygen-free) oxidation, or glycolysis, occurs on the smooth endoplasmic reticulum of the cell. As a result, glucose is torn into 2 parts, and the released energy is sufficient for the synthesis of two ATP molecules.

2. Aerobic (oxygen) oxidation. Two parts of glucose (2 molecules of pyruvic acid) in the presence of oxygen continue a series of oxidative reactions. This stage takes place on the mitochondria and leads to further rupture of molecules and the release of energy.

The result of the second stage of oxidation of one glucose molecule is the formation of 6 carbon dioxide molecules, 6 water molecules and energy, which is enough for the synthesis of 36 ATP molecules.

As substrates for oxidation at the second stage, not only molecules obtained from glucose, but also molecules obtained as a result of the oxidation of lipids, proteins, alcohols, and other energy-intensive compounds can be used.

The active form of acetic acid - A-CoA (acetyl coenzyme A, or acetyl coenzyme A) is an intermediate product of the oxidation of all these substances (glucose, amino acids, fatty acids, and others).

A-CoA is the point of intersection of carbohydrate, protein and lipid metabolism.

With an excess of glucose and other energy-carrying substrates, the body begins to deposit them. In this case, glucose is oxidized in the usual way to lactic and pyruvic acid, then to A-CoA. Further, A-CoA becomes the basis for the synthesis of fatty acids and fat molecules, which are deposited in the subcutaneous adipose tissue. On the contrary, with a lack of glucose, it is synthesized from proteins and fats through A-CoA (gluconeogenesis).

If necessary, the reserves of non-essential amino acids for the construction of certain proteins can also be replenished.

Communication diagram of carbohydrate, lipid, protein and energy metabolism

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The role of carbohydrates in the plant cell. The role of carbohydrates in the body

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Bibliography

1. Chemistry, trans. from English, 2nd ed., M., 1956; Chemistry of carbohydrates, M., 1967

2. Stepanenko B.N., Carbohydrates. Advances in the study of the structure and metabolism, M., 1968

4. Alabin V. G., Skrezhko A. D. Nutrition and health. - Minsk, 1994

5. Sotnik Zh.G., Zarichanskaya L.A. Proteins, fats and carbohydrates. - M., Prior, 2000

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Portal for the student. Self-training

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Bibliography

1. Chemistry, trans. from English, 2nd ed., M., 1956; Chemistry of carbohydrates, M., 1967

2. Stepanenko B.N., Carbohydrates. Advances in the study of the structure and metabolism, M., 1968

4. Alabin V. G., Skrezhko A. D. Nutrition and health. - Minsk, 1994

5. Sotnik Zh.G., Zarichanskaya L.A. Proteins, fats and carbohydrates. - M., Prior, 2000

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