The main pathway of sugar metabolism

The human body needs sugar to provide energy. When you are weak, dizzy, eating a piece of candy can instantly make you energetic. The food the human body eats every day contains sugar, which can be broken down and converted into glucose for the human body to absorb. In daily life, you can eat some sweets appropriately, which are both delicious and can replenish energy, but you cannot eat too much sugary food. On the one hand, it is easy to damage your teeth, and on the other hand, it is easy to cause stomach acid.

Sugar can be metabolized in all tissues of the human body. There are three main pathways, namely anaerobic glycolysis, aerobic oxidation and the pentose phosphate pathway.

(1) Anaerobic glycolysis

The glycolysis process is the process of breaking down glucose into pyruvate, and the whole process has 10 enzyme-catalyzed reactions.

1. Glucose phosphorylation

The first step of glycolysis is the phosphorylation of C6 of glucose catalyzed by hexokinase to form glucose 6-phosphate. This kinase requires Mg2+ ions as a cofactor and consumes one molecule of ATP. The reaction is irreversible.

2. Isomerization of glucose 6-phosphate into fructose 6-phosphate

This is an aldose-ketose isomerization reaction, which is catalyzed by phosphohexose isomerase to convert aldose and ketose into isomers. It requires the participation of Mg2+ ions and is reversible.

3. Phosphorylation of fructose 6-phosphate to produce fructose 1,6-diphosphate

This reaction is the phosphorylation of fructose-6-phosphate to produce fructose-1,6-bisphosphate catalyzed by phosphofructokinase, consuming a second ATP molecule.

4.1,6-diphosphate fructose cleavage

Under the action of aldolase, the bond between C3 and C4 of fructose 6-bisphosphate in hexose phosphate is broken to generate one molecule of 3-phosphoglyceraldehyde and one molecule of dihydroxyacetone phosphate.

5.3-Interconversion of glyceraldehyde phosphate and dihydroxyacetone phosphate

Glyceraldehyde 3-phosphate is the substrate for the next step of glycolysis, so dihydroxyacetone phosphate needs to be converted into glyceraldehyde 3-phosphate under the catalysis of triosephosphate isomerase before further glycolysis.

6.3-Oxidation of glyceraldehyde phosphate

In the presence of NAD+ and H3P04, 3-phosphoglyceraldehyde is catalyzed by 3-phosphoglyceraldehyde dehydrogenase to produce 1,3-diphosphoglycerate. This step is the only oxidation reaction in glycolysis.

7.1, 3-diphosphoglycerate to 3-phosphoglycerate

Under the action of phosphoglycerate kinase, the high-energy phosphoryl group of 1,3-bisphosphoglycerate is transferred to ADP to form ATP and 3-phosphoglycerate.

8. Glycerate-3-phosphate is converted to glycerate-2-phosphate

Under the catalysis of phosphoglycerate mutase, the phosphate group of C3 in the glycerate-3-phosphate molecule is transferred to C2 to form glycerate-2-phosphate, which requires the participation of Mg2+ ions.

9. Glycerate-2-phosphate is converted to phosphoenolpyruvate

Under the catalysis of enolase, glycerate-2-phosphate is dehydrated and the energy within the molecule is redistributed to form phosphoenolpyruvate enol phosphate bonds, which is the second high-energy phosphate compound in the glycolysis pathway.

10. Production of pyruvate

Under the catalysis of pyruvate kinase, the high-energy phosphate group of the phosphoenolpyruvate molecule is transferred to ADP to generate ATP. This is the second substrate-level phosphorylation reaction in the glycolysis pathway. It requires the participation of Mg2+ and K+, and the reaction is irreversible.

(2) Aerobic oxidation (omitted)

(3) Pentose phosphate pathway (omitted)