This is the glycolytic step in which the 6-carbon unit is cleaved to two 3-carbon units. Although there are two products, 3-PGAL and DHAP, only 3-PGAL continues in the glycolytic sequence,and DHAP must be converted to 3-PGAL before it can be further metabolized.
This pair of reactions together involves
1. a dehydrogenation and
2. a substrate level phosphorylation.
Reaction 1 generates an acyl phosphate which has the very high phosphorylating ability necessary to drive reaction 2.
A second molecule of ATP is formed by substrate level phosphorylation.