- Each of the 9 glycolytic intermediates between glucose and pyruvate is phosphorylated. The phosphate group has 3 functions.
- Because the P group is ionized at pH 7 and has charge and because plasma membranes are not permeable to the charged molecules, the phosphorylated molecules can not pass the membranes. They are trapped in the cell.
- Binding of P groups to the active sites of enzymes provides binding energy which decreases the activation energy and increases the specificity of enzyme-catalyzed reactions.
- P groups are necessary for chemical energy. Energy is released after the hydrolysis of ATP.
- Glucose obtained from the diet through intestinal hydrolysis of lactose, sucrose, glycogen, or starch is brought into the hexose phosphate pool through the action of hexokinase.
Free glucose phosphorylated by hexokinase in 1st reaction that was irreversible
- Hexokinase actually traps the glucose in a form that does not diffuse out of the cell. Because phosphorylated sugar molecules do not readily penetrate cell membranes without specific carriers, this commits glucose to further metabolism in the cell.
- In all tissues, the phosphorylation of glucose4 is catalyzed by hexokinase, one of the three regulatory enzymes of glycolysis.