Glycolysis is the process which involves the splitting of glucose(a 6C compound) into two molecules of pyruvic acid (a 3C compound). It occurs in the cytoplasm of the cell. The glycolysis process can be divided into two phases-
• Hexose phase and
• Triose phase.
The end products of glycolysis are two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH.
The reactions involved in the process of glycolysis are as follows:
1. The six carbon glucose molecule is phosphorylated with the presence of ATP to form a glucose-6- phosphate enzyme.
Hexokinase enzyme is used to catalyze this reaction.
2. Then Glucose-6- Phosphate is isomerized by using phosphoglucoisomerase to form a fructose-6- phosphate.
3. The Fructose-6- phosphate obtained from the previous reaction is further phosphorylated using ATP to form fructose 1,6-bisphosphate.
Phosphofructokinase is used to catalyze this reaction, and the ATP is dephosphorylated to form ADP.
4. The Fructose 1,6-bisphosphate gets cleaved by utilizing the enzyme aldolase. It gets cleaved into two molecules of 3 Carbon compounds called dihydroxy acetone phosphate (DHAP) and glyceraldehyde-3- Phosphate. These are isomeric triose compounds.
5. Dihydroxy acetone phosphate (DHAP) and the glyceraldehyde-3- phosphate are interconvertible with the use of triose.
6. Glyceraldehyde-3- phosphate is further phosphorylated and then oxidized in the presence of glyceraldehyde-3- phosphate dehydrogenase to form 1,3- bisphosphoglyceric acid.
7. Then 1,3-bisphosphoglyceric acid is dephosphorylated by phosphoglyceric kinase to form a molecule of 3-phosphoglyceric acid (3-PGA).
8. 3-phosphoglyceric acid (3-PGA) is then further converted by using phosphoglyceric mutase into a molecule of 2-phosphoglyceric acid.
9. 2-phosphoglyceric acid (2-PGA) is further dehydrated by using enolase into a molecule of 2- phosphoenol pyruvic acid.
10. At last 2-phosphoenol pyruvic acid is dephosphorylated to form pyruvic acid and the ADP
is also phosphorylated to form ATP. This reaction is catalyzed by using pyruvic kinase enzyme.
A simple flowchart of steps involvedin glycolysis is shown below :
Glycolysis occurs in both aerobic and anaerobic organisms. After glycolysis, if the cells have oxygen, then it goes on to a process known as a citric acid cycle or tricarboxylic cycle. And if there is no oxygen, then the fermentation process occurs.
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