Structure of Glucose Permease

Because molecules of glucose have two hydroxyl (OH) groups attached, they are too polar to achieve crossing the lipid bilayer of a cell membrane. Glucose permease is the transporter protein specially designed to facilitate the membrane crossing of glucose.

How Permease Binds to Glucose

• Permease binds to glucose in a lock-and-key type fashion. Surface shapes in the glucose permease complement the binding site of the glucose molecule.

What Is 'Binding Energy'?

• Energy is released when glucose binds to permease.

  Energy released when glucose binds to the permease is used by the permease to change its shape and to open, providing access to the other side of the cell membrane. Molecules of glucose are deposited on the inner side beyond the membrane's lipid bilayer.

Glucose Unleashed

• Glucose-6-phosphate

  After being transported across the membrane's lipid bilayer, glucose is set free from the permease transporter and becomes glucose-6-phosphate by phosphorylation.

What Is Phosphorylation?

• Addition of a phosphate group.

  Phosphorylation is the adding of a phosphate group (PO4) to the sixth carbon of the glucose molecule, resulting in enzyme activation.

Purpose of Phosphorylation

• Constant gradient concentration.

  Phosphorylation of glucose into glucose-6-phosphate keeps the permease from transporting glucose back out through the cell membrane and decreases the number of glucose molecules inside the cell to keep the gradient concentration at a constant equilibrium.