Question

Review Figures 9.9 and 10.19. Discuss the roles of intermediate and product played by glyceraldehydes 3-phosphate (G3P) in the two processes shown in these two figures.

Short answer

Glyceraldehyde-3-phosphates play the role of products and intermediates in metabolic reactions such as the Calvin cycle. But it plays a single role in the case of processes like glycolysis.

Step-by-step solution

Definition of glycolysis and the Calvin cycle

Glycolysis is the first and foremost metabolic reaction that involves the breakdown of glucose. It involves the formation of pyruvate by breaking the glucose molecules with the aid of several enzymes.

Calvin cycle is the series of reactions that occurs in a cyclic manner that results in the formation of sugars. It is an important metabolic reaction in plants. It is reactions that act as a source of food.

Role of glyceraldehyde-3-phosphate in the glycolysis

The first figure shows that the glyceraldehyde-3-phosphate acts as an intermediate in the process of glycolysis. Fructose 1,6 bisphosphate is converted into two products in which one molecule is glyceraldehydes 3 phosphate.

The other product formed in this step is the dihydroxyacetone phosphate. It is inter-convertible to glyceraldehydes-3-phosphates by the isomerase enzyme.

Finally, the formation of glycolaldehyde-3-phosphate is the reaction equilibrium establishing step in the glycolysis process. Hence, more amount of G3P is produced.

Role of glyceraldehyde-3-phosphate in the Calvin cycle 

The second figure shows the steps involved in the Calvin cycle. In the case of the Calvin cycle, the glyceraldehyde-3-phosphate is not alone the intermediate. It is the final product of this cycle that further undergoes the process of sugar production.

There are six glyceraldehyde-3-phosphates formed in this reaction, of which one is the product, and the other 5 molecules enter the regeneration phase of this reaction.

Hence, the glyceraldehydes-3-phosphate acts as an intermediate in the glycolysis process. In the Calvin cycle, this component acts as a product and as an intermediate.