What does biochemistry study? Glycolysis is a serious enzymatic process of glucose breakdown that occurs in animal and human tissues 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 regards 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 able to perform certain physiological functions for a certain period of time in conditions of insufficient oxygen.
If the process of glucose breakdown is carried out with the participation of oxygen, aerobic glycolysis occurs.
What is its biochemistry? Glycolysis is considered the first step in the process of oxidizing glucose to water and carbon dioxide.
History Pages
The term "glycolysis" was used by Lépin in the late nineteenth century for the process of reducing blood glucose that was removed from the circulatory system. Some microorganisms have fermentation processes that are similar to glycolysis. For suchtransformation uses eleven enzymes, most of which are 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 reaction of glycolysis, phosphorylation, is associated with the transfer of orthophosphate to glucose by ATP 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 energy of the system, that is, an irreversible chemical process takes place.
Such an enzyme as hexokinase acts as a catalyst for the process of 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 process of phosphorylation of one D-glucose.
Second stage
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 phosphate isomerase into 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 with the help of ATP molecules. The accelerator of this process is the enzyme phosphofructokinase. Reactionis 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, stimulated by AMP and ADP. In the 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-fledged activity of phosphofructokinase by citrate.
If the ratio of ATP to ADP reaches significant values, phosphofructokinase is inhibited, which helps to slow down glycolysis.
How can you increase glycolysis? Biochemistry proposes to reduce the intensity factor for this. For example, in a non-functioning muscle, the activity of phosphofructokinase is low, but the concentration of ATP increases.
When the muscle is working, there is a significant use of ATP, which causes an increase in the level of the enzyme, causing an acceleration of the glycolysis process.
Fourth stage
The enzyme aldolase is the catalyst for this part of glycolysis. Thanks to him, the reversible splitting of the substance into two phosphotrioses occurs. Depending on the temperature value, equilibrium is established at different levels.
How does biochemistry explain what is happening? Glycolysis with increasing temperature proceeds in the direction of a direct reaction, the productwhich is glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
Other stages
The fifth stage is the process of isomerization of triose phosphates. The catalyst for the process is the enzyme triose phosphate isomerase.
The sixth reaction in summary form describes the production of 1,3-diphosphorglyceric acid in the presence of NAD phosphate as a hydrogen acceptor. It is this inorganic agent that removes hydrogen from glyceraldehyde. The resulting bond is fragile, but it is rich in energy, and when cleaved, 1, 3-diphosphoglyceric acid is obtained.
The seventh step, catalyzed by phosphoglycerate kinase, involves the transfer of energy from the phosphate residue to ADP to form 3-phosphoglyceric acid and ATP.
In the eighth reaction, an intramolecular transfer of the phosphate group occurs, while the transformation of 3-phosphoglyceric acid into 2-phosphoglycerate is observed. The process is reversible, therefore magnesium cations are used for its implementation.
2,3-diphosphoglyceric acid acts as a cofactor for the enzyme at this stage.
The ninth reaction involves the transition of 2-phosphoglyceric acid to phosphoenolpyruvate. The enolase enzyme, which is activated by magnesium cations, acts as an accelerator of this process, 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 reduction of pyruvic acid, obtaining lactic acid. This conversion requires the participation of the enzyme lactate dehydrogenase.
How can you write down glycolysis in a general way? Reactions, the biochemistry of which was discussed above, is reduced to glycolytic oxidoreduction, accompanied by the formation of ATP molecules.
Process value
We looked at how the biochemistry describes glycolysis (reactions). The biological significance of this process is to obtain phosphate compounds with a large energy reserve. If two ATP molecules are spent at the first stage, then the stage is associated with the formation of four molecules of this compound.
What is its biochemistry? Glycolysis and gluconeogenesis are energy efficient: 2 ATP molecules account for 1 glucose molecule. The energy change during the formation of two acid molecules from glucose is 210 kJ/mol. 126 kJ leaves 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 deals with similar calculations. Aerobic and anaerobic glycolysis have an efficiency 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 reactions of glycolysis are close to thermodynamic equilibrium, three processes are associated with a significant decrease in the amount of free energy, and are considered irreversible.
What is gluconeogenesis? The biochemistry of the process consists in the breakdown of carbohydrate, which takes place inseveral stages. Each step is controlled by enzymes. For example, in tissues that are characterized by aerobic metabolism (tissues of the heart, kidneys), it is regulated by 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 characterizes anaerobic glycolysis? Biochemistry, for example, involves the inclusion of other carbohydrates in the process.
As a result of laboratory studies, it was found that about 80% of the fructose that enters the human body 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 resulting compound is converted into glucose through several stages, accompanied by the elimination 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 be converted into fructose-1,6-diphosphate.
Then this substance is metabolized through the stages characteristic of glycolysis. The muscles and liver have 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 decomposes under the influence of ketose-1-phosphate aldolase into glyceraldehyde and dihydroxyacetone phosphate. D-glyceraldehyde underunder the influence of triozokinase, it enters phosphorylation, ultimately ATP molecules are released and dihydroxyacetone phosphate is obtained.
Congenital anomalies
Biochemists have been able to identify some congenital anomalies associated with fructose metabolism. This phenomenon (essential fructosuria) is associated with a biological deficiency in the content of the enzyme ketohexokinase in the body, therefore, 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 around 0.73 mmol/L.
Participation in the biosynthesis of galactose
Galactose enters the body with food, which is broken down in the digestive tract to glucose and galactose. First, this carbohydrate is converted into galactose-1-phosphate, the process is catalyzed by galactokinase. Next, 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.
Besides this pathway of galactose metabolism, a second scheme is also possible. First, galactose-1-phosphate is also formed, but subsequent steps are associated with the formation of UTP molecules and glucose-1-phosphate.
Among the numerous pathological conditions associated with carbohydrate metabolism, galactosemia occupies a special place. This phenomenon is associated with a recessively inherited disease, within which the blood sugar content rises due to galactose and reaches 16.6 mmol / l. At the same time, 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 diagnosed with galactosemia have mental retardation and also have cataracts.
As the growth of carbohydrate metabolism disorders decrease, the reason is the breakdown of galactose along the second path. Thanks to the fact that biochemists managed to find out the essence of the ongoing process, it became possible to deal with problems related to the incomplete breakdown of glucose in the body.
