What does biochemistry study? Glycolysis is a serious enzymatic process of glucose breakdown that occurs in the tissues of animals and humans without the use of oxygen. It is he who is considered by biochemists as a way to obtain lactic acid and ATP molecules.
Definition
What is aerobic glycolysis? Biochemistry considers this process as the only process characteristic of living organisms that supplies energy.
It is with the help of such a process that the organism of animals and humans is capable of performing certain physiological functions for a certain period of time under conditions of insufficient oxygen.
If the process of splitting glucose is carried out with the participation of oxygen, aerobic glycolysis proceeds.
What is its biochemistry? Glycolysis is considered the first step in the process of oxidizing glucose to water and carbon dioxide.
Pages of history
The term “glycolysis” was used by Lepin at the end of the nineteenth century for the process of reducing glucose in the blood, which was withdrawn from the circulatory system. Some microorganisms have fermentation processes that are similar to glycolysis. Eleven enzymes are used for such a conversion, most of them being isolated in a homogeneous, highly purified or crystalline form, their properties are well studied. This process takes place in the hyaloplasm of the cell.
Process specifics
How does glycolysis proceed? Biochemistry is a science in which this process is considered as a multi-stage reaction.
The first enzymatic glycolysis reaction, phosphorylation, is associated with the transfer of glucose by ATP orthophosphate molecules. The enzyme hexokinase acts as a catalyst in this process.
The production of glucose-6-phosphate in this process is explained by the release of a significant amount of system energy, that is, an irreversible chemical process proceeds.
An enzyme such as hexokinase acts as a catalyst for the phosphorylation of not only D-glucose itself, but also D-mannose, D-fructose. In addition to hexokinase, there is another enzyme in the liver - glucokinase, which catalyzes the phosphorylation of D-glucose alone.
Second phase
How does modern biochemistry explain the second stage of this process? Glycolysis at this stage is the transition of glucose-6-phosphate under the influence of hexose phosphatisomerase to a new substance - fructose-6-phosphate.
The process proceeds in two mutually opposite directions, does not require cofactors.
Third stage
It is associated with the phosphorylation of the resulting fructose-6-phosphate using ATP molecules. The accelerator of this process is the enzyme phosphofructokinase. The reaction is considered irreversible, it occurs in the presence of magnesium cations, it is considered a slowly proceeding stage of this interaction. It is she who is the basis for determining the rate of glycolysis.
Phosphofructokinase is one of the representatives of allosteric enzymes. It is inhibited by ATP molecules, stimulate its AMP and ADP. In case of diabetes, during fasting, as well as in many other conditions in which fats are consumed in large quantities, the citrate content in tissue cells increases several times. Under such conditions, there is a significant inhibition of the full activity of phosphofructokinase citrate.
If the ratio of ATP to ADP reaches significant values, phosphofructokinase is inhibited, which helps to slow down glycolysis.
How can glycolysis be increased? Biochemistry suggests reducing the intensity factor for this. For example, in a non-functioning muscle, phosphofructokinase activity is low, but the concentration of ATP increases.
When the muscle is working, significant use of ATP is observed, which causes an increase in the level of the enzyme, and accelerates the process of glycolysis.
Fourth stage
The catalyst for this part of glycolysis is the aldolase enzyme. Thanks to it, a reversible splitting of the substance into two phosphotrioses occurs. Depending on the temperature value, equilibrium is established at different levels.
How does biochemistry explain? Glycolysis with an increase in temperature proceeds in the direction of a direct reaction, the product of which is glyceraldehyde-3-phosphate and dioxiaacetonphosphate.
Other stages
The fifth stage is the process of isomerization of triosophosphates. The catalyst of the process is the enzyme triosephosphatisomerase.
The sixth reaction in summary describes the production of 1,3-diphosphosphoriclinic acid in the presence of NAD phosphate as a hydrogen acceptor. It is this inorganic agent that cleaves hydrogen from glyceral always. The resulting bond is fragile, but it is rich in energy, and upon splitting, 1,3-diphosphoglyceric acid is obtained.
The seventh stage is catalyzed by phosphoglycerate kinase, involves the transfer of energy by the phosphate residue to ADP with the formation of 3-phosphoglyceric acid and ATP.
In the eighth reaction, intramolecular transfer of the phosphate group occurs, while the conversion of 3-phosphoglyceric acid to 2-phosphoglycerate is observed. The process is reversible, therefore, magnesium cations are used for its implementation.
The cofactor of the enzyme at this stage is 2,3-diphosphoglyceric acid.
The ninth reaction involves the conversion of 2-phosphoglyceric acid to phosphoenolpyruvate. The accelerator of this process is the enzyme enolase, which is activated by magnesium cations, and fluoride acts as an inhibitor in this case.
The tenth reaction involves breaking the bond and transferring the energy of the phosphate residue to ADP from phosphoenolpyruvic acid.
The eleventh stage is associated with the restoration of pyruvic acid, obtaining lactic acid. To carry out this transformation, the participation of the enzyme lactate dehydrogenase is necessary.
How can glycolysis be written in general terms? The reactions whose biochemistry was considered above are reduced to glycolytic oxidoreduction, accompanied by the formation of ATP molecules.
Process value
We examined how the biochemistry of glycolysis (reaction) describes. The biological significance of this process is to obtain phosphate compounds with a large energy reserve. If at the first stage two ATP molecules are expended, then the stage is associated with the formation of four molecules of this compound.
What is its biochemistry? Glycolysis and gluconeogenesis have energy efficiency: 1 molecule of glucose per 2 ATP molecules. The change in energy during the formation of two acid molecules from glucose is 210 kJ / mol. 126 kJ is expelled in the form of heat, 84 kJ accumulates in the phosphate bonds of ATP. The terminal bond has an energy value of 42 kJ / mol. Biochemistry also deals with such calculations. Glycolysis aerobic and anaerobic have a coefficient of performance of 0.4.
Interesting Facts
As a result of numerous experiments, it was possible to establish the exact values of each glycolysis reaction occurring in intact human erythrocytes. Eight glycolysis reactions are close to thermodynamic equilibrium, three processes are associated with a significant decrease in free energy, are considered irreversible.
What is gluconeogenesis? The biochemistry of the process is the breakdown of carbohydrate, proceeding in several stages. Control over each stage is carried out by enzymes. For example, in tissues that are characterized by aerobic metabolism (heart, kidney tissue), it is regulated by the isoenzymes LDH1 and LDH2. They are inhibited by small amounts of pyruvate, as a result of which the synthesis of lactic acid is not allowed, and the complete oxidation of acetyl-CoA in the tricarboxylic acid cycle is achieved.
What else is characterized by anaerobic glycolysis? Biochemistry, for example, involves the inclusion of other carbohydrates in the process.
As a result of laboratory studies, it was possible to establish that about 80% of fructose, which enters the human body along with food, is metabolized in the liver. Here, the process of its phosphorylation to fructose-6-phosphate takes place, the enzyme hexokinase acts as a catalyst for this process.
This process is inhibited by glucose. The compound obtained is converted into glucose through several stages, accompanied by the removal of phosphoric acid. In addition, its subsequent transformations into other phosphorus-containing organic compounds are possible.
Under the influence of ATP and phosphofructokinase, fructose-6-phosphate will produce fructose-1,6-diphosphate.
Then this substance is metabolized in stages characteristic of glycolysis. In the muscles and liver, there is ketohexokinase, which can accelerate the process of phosphorylation of fructose into its phosphorus-containing compound. The process is not blocked by glucose, and the resulting fructose-1-phosphate breaks down under the influence of ketose-1-phosphataldolase into glyceraldehyde and dihydroxyacetone phosphate. D-glyceraldehyde under the influence of triosokinase enters phosphorylation, eventually ATP molecules are secreted and dihydroxyacetone phosphate is obtained.
Congenital malformations
Biochemists have been able to identify some congenital anomalies associated with the exchange of fructose. This phenomenon (essential fructosuria) is associated with a biological deficiency of the ketohexokinase enzyme in the body, so all processes of the breakdown of this carbohydrate are inhibited by glucose. The consequence of this violation is the accumulation of fructose in the blood. For fructose, the renal threshold is low, so fructosuria can be detected at blood carbohydrate concentrations of about 0.73 mmol / L.
Participation in galactose biosynthesis
Galactose enters the body with food, which is broken down in the digestive tract to glucose and galactose. First, this carbohydrate is converted to galactose-1-phosphate, galactokinase acts as a catalyst for the process. Then, the phosphorus-containing compound is converted to glucose-1-phosphate. At this stage, uridine diphosphogalactose and UDP glucose are also formed. The subsequent stages of the process proceed according to a scheme similar to the breakdown of glucose.
In addition to this pathway of galactose metabolism, a second scheme is also possible. At first, galactose-1-phosphate is also formed, but the subsequent steps are associated with the formation of UTP and glucose-1-phosphate molecules.
Among the numerous pathological conditions associated with carbohydrate metabolism, galactosemia occupies a special place. This phenomenon is associated with a recessively inherited disease in which the blood sugar content rises due to galactose and reaches 16.6 mmol / L. In this case, there is practically no change in the content of glucose in the blood. In addition to galactose, in such cases, galactose-1-phosphate also accumulates in the blood. Children with galactosemia have mental retardation and cataracts.
As growth, carbohydrate metabolism disorders decrease, the cause is the occurrence of galactose cleavage along the second path. Due to the fact that biochemists managed to find out the essence of the process, it became possible to deal with problems related to the incomplete breakdown of glucose in the body.