Glycerate 3-phosphate

Glycerate 3-phosphate (GP) or 3-phosphoglycerate (3PG) is a biochemically significant 3-carbon molecule that is a metabolic intermediate in both glycolysis and the Calvin cycle. This chemical is often termed PGA when referring to the Calvin cycle. 3-phosphoglycerate is the resultant of the split of 6 carbon intermediate that is so unstable it splits instantly. And two 3-phosphoglycerate is produced for each molecule of CO2

Calvin cycle
In the Calvin cycle, two glycerate 3-phosphate molecules are reduced to form two molecules of glyceraldehyde 3-phosphate (PGAL). This is the first compound formed during the C3 or Calvin cycle. It is a reactive biomolecule which is easily reduced.

Amino acid synthesis
Glycerate 3-phosphate is also a precursor for serine, which in turn, can create several other amino acids (such as glycine.)