How is glycerate 3-phosphate reduced to triose phosphate using reduced NADP and ATP?

Sourav PanNovember 9, 2024

Answered

In the Calvin cycle, glycerate 3-phosphate (3-PGA) is reduced to glyceraldehyde 3-phosphate (G3P), also known as triose phosphate, using ATP and reduced NADP++ (NADPH). This reduction process is essential for converting fixed carbon into a form that can be utilized to synthesize carbohydrates. Here’s a detailed overview of how this reduction occurs:

Steps in the Reduction of Glycerate 3-Phosphate

1. Formation of 3-PGA:
   • The Calvin cycle begins with the carboxylation of ribulose bisphosphate (RuBP) by the enzyme RuBisCO, producing two molecules of 3-PGA for each CO₂ molecule fixed.
2. Phosphorylation of 3-PGA:
   • In the first step of the reduction phase, each molecule of 3-PGA is phosphorylated by ATP. This reaction is catalyzed by the enzyme phosphoglycerate kinase, converting 3-PGA into 1,3-bisphosphoglycerate (1,3-BPG). The reaction can be summarized as:
   3 PGA+ATP→1 3 BPG+ADP
3. Reduction of 1,3-BPG:
   • The next step involves the reduction of 1,3-BPG to G3P. This reaction is catalyzed by the enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which utilizes NADPH as a reducing agent. NADPH donates electrons and a proton to 1,3-BPG, resulting in the formation of G3P and oxidizing NADPH to NADP++. The reaction can be represented as:
   1 3 BPG+NADPH+H+→G3P+NADP++Pi
4. Production of Glyceraldehyde 3-Phosphate (G3P):
   • The final product of this reduction process is glyceraldehyde 3-phosphate (G3P), a three-carbon sugar phosphate that can be used to synthesize glucose and other carbohydrates or be recycled to regenerate RuBP in the Calvin cycle.