Products of Glycolysis

Glycolysis is an important pathway in cellular respiration. The word ‘Gluco’ means glucose or sugar, and ‘lysis’ refers to breakage or cutting. It undergoes a series of reactions, which happens in the cytoplasm of the animal cell. Glycolysis does not need molecular oxygen.  At each step, each product of glycolysis will be formed, which is used for different means. The breakdown products of glycolysis are 4 pyruvate molecules, 2 NADH molecules, and 2 ATP molecules. These were the products of glycolysis used in cellular respiration.

Phases of Glycolysis

There are two phases present in glycolysis: the preparatory phase and the payoff phase.

• Preparatory phase: There are 3 enzymatic reactions like phosphorylation, isomerization, and phosphorylation II. In this phase, the glucose is converted into fructose 1,6- bisphosphate with the consumption of 2 ATP. In phosphorylation, fructose 1,6- bisphosphate is further broken down into the glyceraldehyde 3-phosphate and dihydroxyacetone phosphate (DHAP). And the dihydroxyacetone phosphate is isomerized into glyceraldehyde-3- phosphate (2 molecules). Throughout this preparatory phase, glucose is converted into glyceraldehyde 3-phosphate(2 molecules).
• Payoff phase: In the payoff phase, the glyceraldehyde 3-phosphate (2 molecules) is further converted into 4 ATP and pyruvate(2 molecules).

Products of Glycolysis

Preparatory Phase

• Glucose 6-phosphate: The glucose with the help of one ATP performs the glycolytic reaction to form the Glucose 6-phosphate, one ADP, and one H+.

Glucose + ATP → Glucose 6-phosphate + ADP + H+

This reaction is an irreversible reaction and the product is used in the synthesis of glycogen and galactose. In addition, glucose 6-phosphate supports the pentose phosphate pathway. For these reactions, the catalysis is kinases and transferases.

• Fructose 6-phosphate: The glucose 6-phosphate undergoes isomerization and forms a fructose 6-phosphate. Here the aldose is directly isomerized into the ketose with the help of catalysis. The catalysts used are phosphoglucose isomerase or glucose phosphate isomerase or phosphohexose isomerase. 

Glucose 6-phosphate ⇄ Fructose 6-phosphate It is a reversible reaction.

• Fructose 1,6-bisphosphate: The Fructose 6-phosphate is converted into the fructose 1,6-bisphosphate and one ADP and one H+. This is called the phosphorylation II reaction. The catalyst used here is Phosphofructokinase 1, and it is an irreversible reaction. Here, the ketose is converted into aldolase.

Fructose 6-phosphate + ATP → Fructose 1,6-bisphosphate + ADP + H+

• Dihydroxyacetone phosphate and  Glyceraldehyde 3-phosphate: In this reaction, the aldolase is cleaved back into ketose and aldose. The Fructose 1,6-bisphosphate split into the Glyceraldehyde 3-phosphate and Dihydroxyacetone phosphate. It is a reversible cleavage, catalysed by Fructose 1,6-bisphosphate itself. 

Fructose 1,6-bisphosphate ⇄ Dihydroxyacetone phosphate + Glyceraldehyde 3-phosphate

• Interconversion phase: Glyceraldehyde 3-phosphate and Dihydroxyacetone phosphate interconvert themselves to undergo the glycolytic pathway. The Dihydroxyacetone phosphate is converted into the Glyceraldehyde 3-phosphate with the help of a catalyst, triosephosphate isomerase.

Dihydroxyacetone phosphate ⇄ Glyceraldehyde 3-phosphate

These two molecules of Glyceraldehyde 3-phosphate undergo the second glycolytic pathway.

Dihydroxyacetone phosphate + NADH + H+ ⇄ Glycerol 3-phosphate + NAD+

Now, Dihydroxyacetone phosphate turns into the Glycerol 3-phosphate. It is used in lipid metabolism and synthesis. It is present in the small intestine and adipose tissue.

Payoff Phase

• 1,3-Bisphosphoglycerate: We have two reactions in this process. Firstly, the Glyceraldehyde 3-phosphate is oxidised into the 1,3-Bisphosphoglycerate. The catalyst used is glyceraldehyde 3-phosphate dehydrogenase. The oxidising agent is NAD+.

Glyceraldehyde 3-phosphate + NAD+ + Pi ⇄ 1,3-Bisphosphoglycerate + NADH + H+

Here, chemical energy is required for ATP synthesis. In another reaction, enolase is the catalyst.

1,3-bisphosphoglycerate is converted into acyl phosphate, an anhydride.

1,3-bisphosphoglycerate ⇄  acyl phosphate.

• 3-Phosphoglycerate: The 1,3-Bisphosphoglycerate turns into 3-Phosphoglycerate and one ATP. It is the first reaction where ATP is formed. The catalysts are phosphoglycerate kinase.

1,3-Bisphosphoglycerate + ADP + H+ ⇄ 3-Phosphoglycerate + ATP

• 2-Phosphoglycerate: The 3-Phosphoglycerate is converted into the 2-Phosphoglycerate by the Rapoport Luebering pathway.

3-Phosphoglycerate ⇄ 2-Phosphoglycerate

1. Phosphoenolpyruvate: Here, the enol, Phosphoenolpyruvate is formed by the dehydration of 2-Phosphoglycerate. It uses enolase as the catalyst. 

2-Phosphoglycerate ⇄ Phosphoenolpyruvate + H2O

• Pyruvate: The phosphoryl group is transferred from the phosphoenolpyruvate to ADP. It results in a pyruvate molecule and one ATP. Pyruvate kinase is the rate-limiting enzyme that catalyses the activity.

Phosphoenolpyruvate + ADP + H+ → Pyruvate + ATP

Breakdown products of glycolysis

As a result of each step in glycolysis, 4 pyruvate molecules, 2 NADH molecules, and 2 ATP molecules are formed. In total, 4 ATP molecules are formed but initially, we are using two molecules. It will be 2 molecules formed at the end. 

What products of glycolysis are used in cellular respiration?

• The products of glycolysis are used in cellular respiration are two pyruvate molecules, two NADH molecules, and two ATP molecules. 
• In our body, mature RBCs cannot perform aerobic respiration due to the absence of mitochondria in it. So, glycolysis is a very important metabolic pathway that supplies energy to it. 
• Red blood cells, cancer cells, stem cells use ATP produced from the glycolytic pathway. The NAD+ molecules help red blood cells to produce ATP sufficiently. 
• The pyruvate molecules are used in the cellular respiration of the Krebs cycle, which supplies the energy to the cells.

Conclusion

Glycolysis is the process of breaking glucose into energy. It mainly produces four pyruvate molecules, two NADH molecules, and two ATP molecules. Glycolysis happens in two phases with a set of ten reactions. In each reaction, different products will be formed by the reactions like phosphorylation, isomerization, dehydration, oxidation. It is an aerobic breakdown that automatically enters into the citric acid cycle and oxidative phosphorylation for the production of more ATP molecules. The products of glycolysis used in cellular respiration were explained with their importance.