Жануарлардағы энергия қоры - гликоген

Glucose polymer used as energy store in animals

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. It is the main storage form of glucose in the human body. Glycogen functions as one of three regularly used forms of energy reserves, creatine phosphate being for very short term, glycogen being for short term and the triglyceride stores in adipose tissue (i. e., body fat) being for long term storage. Protein, broken down into amino acids, is seldom used as a main energy source except during starvation and glycolytic crisis (see bioenergetic systems). In humans, glycogen is made and stored primarily in the cells of the liver and skeletal muscle. In skeletal muscle, glycogen is found in a low concentration (1–2% of the muscle mass): the skeletal muscle of an adult weighing 70 kg stores roughly 400 grams of glycogen. white blood cells, and glial cells in the brain. The uterus also stores glycogen during pregnancy to nourish the embryo. The amount of glycogen stored in the body mostly depends on oxidative type 1 fibres, physical training, basal metabolic rate, and eating habits. Different levels of resting muscle glycogen are reached by changing the number of glycogen particles, rather than increasing the size of existing particles

Approximately 4 grams of glucose are present in the blood of humans at all times;

Glycogen is a branched biopolymer consisting of linear chains of glucose residues with an average chain length of approximately 8–12 glucose units and 2,000 60,000 residues per one molecule of glycogen. Like amylopectin, glucose units are linked together linearly by α(1→4) glycosidic bonds from one glucose to the next. Branches are linked to the chains from which they are branching off by α(1→6) glycosidic bonds between the first glucose of the new branch and a glucose on the stem chain. Each glycogen is essentially a ball of glucose trees, with around 12 layers, centered on a glycogenin protein, with three kinds of glucose chains: A, B, and C. There is only one C chain, attached to the glycogenin. This C chain is formed by the self glucosylation of the glycogenin, forming a short primer chain. From the C chain grows out B chains, and from B chains branch out B and A chains. The B chains have on average 2 branch points, while the A chains are terminal, thus unbranched. On average, each chain has length 12, tightly constrained to be between 11 and 15. All A chains reach the spherical surface of the glycogen. Glycogen in muscle, liver, and fat cells is stored in a hydrated form, composed of three or four parts of water per part of glycogen associated with 0.45 millimoles (18 mg) of potassium per gram of glycogen. Glucose is an osmotic molecule, and can have profound effects on osmotic pressure in high concentrations possibly leading to cell damage or death if stored in the cell without being modified. Other cells that contain small amounts use it locally as well. As muscle cells lack glucose 6 phosphatase, which is required to pass glucose into the blood, the glycogen they store is available solely for internal use and is not shared with other cells. This is in contrast to liver cells, which, on demand, readily do break down their stored glycogen into glucose and send it through the blood stream as fuel for other organs. Skeletal muscle needs ATP (provides energy) for muscle contraction and relaxation, in what is known as the sliding filament theory. Skeletal muscle relies predominantly on glycogenolysis for the first few minutes as it transitions from rest to activity, as well as throughout high intensity aerobic activity and all anaerobic activity. During anaerobic activity, such as weightlifting and isometric exercise, the phosphagen system (ATP PCr) and muscle glycogen are the only substrates used as they do not require oxygen nor blood flow. The level of exercise intensity determines how much of which substrate (fuel) is used for ATP synthesis also. Muscle glycogen can supply a much higher rate of substrate for ATP synthesis than blood glucose. During maximum intensity exercise, muscle glycogen can supply 40 mmol glucose/kg wet weight/minute, whereas blood glucose can supply 4 5 mmol. This reliance on muscle glycogen is not only to provide the muscle with enough ATP during high intensity exercise, but also to maintain blood glucose homeostasis (that is, to not become hypoglycaemic by the muscles needing to extract far more glucose from the blood than the liver can provide). However, research by Besford et al used small angle X ray scattering experiments accompanied by branching theory models to show that glycogen is a randomly hyperbranched polymer nanoparticle. Glycogen is not fractal in nature. This has been subsequently verified by others who have performed Monte Carlo simulations of glycogen particle growth, and shown that the molecular density reaches a maximum near the centre of the nanoparticle structure, not at the periphery (contradicting a fractal structure that would have greater density at the periphery).

Glycogen was discovered by Claude Bernard. His experiments showed that the liver contained a substance that could give rise to reducing sugar by the action of a "ferment" in the liver. By 1857, he described the isolation of a substance he called "la matière glycogène", or "sugar forming substance". Soon after the discovery of glycogen in the liver, A. Sanson found that muscular tissue also contains glycogen. The empirical formula for glycogen of n was established by Kekulé in 1858.

Glycogen synthesis is, unlike its breakdown, endergonic—it requires the input of energy. Energy for glycogen synthesis comes from uridine triphosphate (UTP), which reacts with glucose 1 phosphate, forming UDP glucose, in a reaction catalysed by UTP—glucose 1 phosphate uridylyltransferase. Glycogen is synthesized from monomers of UDP glucose initially by the protein glycogenin, which has two tyrosine anchors for the reducing end of glycogen, since glycogenin is a homodimer. After about eight glucose molecules have been added to a tyrosine residue, the enzyme glycogen synthase progressively lengthens the glycogen chain using UDP glucose, adding α(1→4) bonded glucose to the nonreducing end of the glycogen chain. The glycogen branching enzyme catalyzes the transfer of a terminal fragment of six or seven glucose residues from a nonreducing end to the C 6 hydroxyl group of a glucose residue deeper into the interior of the glycogen molecule. The branching enzyme can act upon only a branch having at least 11 residues, and the enzyme may transfer to the same glucose chain or adjacent glucose chains.

The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted. Restoration of normal glucose metabolism usually normalizes glycogen metabolism, as well. In hypoglycemia caused by excessive insulin, liver glycogen levels are high, but the high insulin levels prevent the glycogenolysis necessary to maintain normal blood sugar levels. Glucagon is a common treatment for this type of hypoglycemia. Various inborn errors of carbohydrate metabolism are caused by deficiencies of enzymes or transport proteins necessary for glycogen synthesis or breakdown. These are collectively referred to as glycogen storage diseases.