The entire biochemical activity of an animal cell can be described by two verbs: “store” and “spend”. The younger the body, the more the processes of synthesis and storage of organic substances will prevail over their breakdown and expenditure. The explanation is simple: to grow and "build" your body, you need a lot of plastic material and, of course, energy. The main building block of the cell is protein, and glycogen is the dominant energy-generating compound.
It is considered a reserve carbohydrate, which is stored in the cells of the liver and skeletal muscles of all mammals: both animals and humans. This work will be devoted to the study of its properties.
What and where do we stock
At the level of the animal cell, organic substances are synthesized and accumulate in its structural units - organelles. Proteins are synthesized in ribosomes, lipids and carbohydrates - in the channels of the smooth endoplasmic reticulum. In the body of mammals, stocks of organic substances accumulate in skeletal muscle, liver, subcutaneous fat and omentum. The stock carbohydrate of animals is glycogen, which is synthesized from glucose in the blood.
It is formed as a product of the dissimilation of food products, which primarily include plant starch: bread, potatoes, rice. These substances are broken down in the oral cavity, stomach, and also in the duodenum. It is in it that their main decay occurs. The resulting glucose is absorbed into the blood capillaries of the villi of the small intestine and then spreads by blood to the muscles and liver, where the reserve carbohydrate of animals and humans is synthesized.
What is glycogen
Although the name of the substance contains a part of the word “glycos”, which means “sweet” in Greek, it has almost no taste. Most likely, this name indicates its belonging to the class of complex carbohydrates containing glucose residues, which is really sweet in taste. Glycogen has the appearance of a structureless white powder. It is hydrophilic and forms a colloidal solution similar to milk. As a storage carbohydrate in an animal cell, the polysaccharide is hydrolyzed in an acidic environment in several stages. The products of its interaction with water are dextrins, then maltose and, finally, glucose. Being a polymer, glycogen has the form of a mixture of branched chain molecules of various weights.
Biochemical properties
We have established the fact that glycogen is a storage carbohydrate of an animal cell. Reserve substances of this type undergo two mutually opposite processes in the cytoplasm of hepatocytes, leukocytes and myocytes. The first is dissimilation, which leads to the release of glucose molecules, and the second is assimilation, which translates the excess glucose into a reserve polymer, glycogen. It accumulates in the body and is a reserve of energy used in the process of life of an animal and a person.
How animal starch is synthesized
Recall that, from a chemical point of view, it is a high molecular weight compound - a polymer, the monomers of which are α-d glucose residues. In order for them to bind to each other by glycosidic bonds, activation, that is, "swinging" of the sigma bonds of the carbon skeleton of hexose, is necessary. This is achieved in the so-called hexokinase reaction. Spare animal carbohydrates are synthesized from glucose-6-phosphate. This substance is a product of the hexokinase reaction. The enzyme catalyzing the above mechanism is contained in the cytoplasm of kidney cells, the mucous layer of the small intestine and liver of animals and humans.
Glycogen breakdown
As we already found out earlier, starch - glycogen - is a reserve carbohydrate in an animal cell. Biochemical studies have established that its cleavage cannot occur without the participation of a specific enzyme, phosphorylase. It works in an acidic environment in the presence of inorganic phosphate molecules. The enzyme itself becomes active under the influence of the hormone of the pancreas - glucagon. Its presence in the blood indicates that the level of glucose in it is low. Therefore, the animal body mobilizes the resources of the stored carbohydrate - glycogen and begins to break it down to get an additional portion of glucose.
This process is called glycogenolysis. Neurophysiologists have found that stress hormones - adrenaline and norepinephrine produced by the adrenal glands, also provoke glycogenolysis.
The liver and its role in carbohydrate metabolism
In biology, this largest mammalian digestive gland is called a biochemical factory. Indeed, a lot of enzymatic reactions occur in it, providing metabolism and energy, that is, metabolism. As is already known, glycogen is the storage carbohydrate in the animal cell. Its breakdown quickly leads to the saturation of blood with glucose - the main source of energy for all mammals and humans.
Lost animal starch is replenished in their organisms by ingestion of starchy foods: potatoes, bread, rice. All these products undergo digestion in the digestive tract, and the resulting glucose enters the bloodstream, and from it into the cells, especially skeletal muscle and liver. In them, the synthesis of animal starch occurs under the action of an enzyme, glucopyrophosphorylase.
What processes occur in skeletal muscle
As in the liver, animal starch accumulates in myocytes - muscle cells. Since the mass of muscles is much greater than the weight of the liver, the glycogen content in them is much higher. During physical exertion, animal starch begins to break down. Lactic acid, formed as a result of glycolysis, enters the bloodstream and is transferred to liver and kidney cells. In them, out of every two lactic acid molecules, one mole of glucose is synthesized, which is then converted into a reserve polysaccharide. The reaction occurs using the energy of ATP. Thus, glycogen accumulated by myocytes, hepatocytes, cells of the renal cortical layer, myocardium and lung cells is the reserve carbohydrate of the animal cell.
The role of enzymes in the exchange of animal starch
As previously established, a spare carbohydrate in animal cells is called glycogen. As a result of two mutually opposite directions in metabolism: splitting and synthesis, it also participates in these reactions. The mutual conversion of glucose into glycogen and vice versa is possible only with the participation of a complex enzymatic system in these reactions. It includes glycogenogenesis catalysts, such as phosphoglucomutase (converts glucose-6-phosphate to glucose-1-phosphate) and UDP-glucopyrophosphorylase (provides irreversibility of glycogen synthesis). Cleavage reactions occur in the presence of glycogen phosphorylase and two more enzymes that sequentially cleave the side branches in glycogen chains. The system of all the above enzymes acts only on the exchange of glycogen in a heterotrophic animal cell, therefore, the correct answer to the test question: is a reserve carbohydrate in an animal cell: 1. Starch, 2 Glycogen? - there will be a statement at number 2.
Disorders of carbohydrate metabolism and its consequences
Based on the above facts, we have found that glycogen is the storage carbohydrate in the animal cell. Violations of its metabolism can be caused by two types of reasons. The first - errors in nutrition and lifestyle, the second - congenital malformations in the work of the enzymatic system of the body. The totality of enzymes related to it is responsible both for the breakdown of animal starch, and for its formation from glucose in the blood. Therefore, pathologies arise both in plastic metabolism and energy reactions. They are called glycogenoses. As was determined above, glycogen, which accumulates primarily in the liver and skeletal muscles, is the storage carbohydrate in the animal cell. Hence two types of syndromes: muscular and hepatic etiology. The first group includes McArdle disease. The patient does not produce the phosphorylase enzyme. This leads to the appearance in the urine of a chromoprotein - myoglobin, which is released during heavy physical work. As a result, muscle tissue is destroyed and convulsive conditions appear.
Girke's disease belongs to hepatic syndromes . It is most common since infancy. Patients in the liver cells do not have an enzyme that converts the product of the primary breakdown of glycogen into glucose, so a very low sugar level (hypoglycemia) is observed in the patient’s blood, and acetone appears in the urine, which causes intoxication of the body.
In this article, we examined the mechanisms of exchange of animal starch - glycogen that occurs in mammalian and human cells.