In the fourth step the six-carbon molecule is split into two non-identical three-carbon molecules, while in the fifth step, one of these three-carbon molecules is rearranged by an isomerase to produce two identical three-carbon molecules. 

The second step involves an isomerase enzyme that rearranges the glucose-6-phospahte molecule to form fructose-6-phosphate. 

In the third step, phosphofructokinase adds an additional phosphate group to fructose-6-phosphate forming Fructose-1, 6-bisphospahate in an irreversible reaction.

Preparatory phase has two steps that require ATP.

The first step involves the addition of a phosphate group to the glucose molecule to prevent it from leaving the cell and this reaction is reversible.