First Step - Glucose Phosphorylation

The first step as soon as the glucose enters the cell is that it undergoes immediate phosphorylation. So that it cannot diffuse out of the cell. This is because, on phosphorylation, the glucose becomes polar and hence cannot flow across the plasma membrane passively.

This step functions at the expense of an ATP. Glucose reacts with an inorganic phosphate available from ATP and converts into glucose 6-phosphate. i.e., a phosphate group is added to the 6th carbon of Glucose.

This reaction is catalyzed by the enzyme glucokinase or hexokinase.

# I wrote the reaction above in the picture.