bmed2301 glycogen metabolism

Blood glucose level is maintained at…

80-100 mg/dL

Regulation of blood glucose level

• digest and absorb carbohydrates as glucose

• make glucose by gluconeogenesis

• convert glucose to glycogen for storage

Glycogen in muscles

• quick source of energy for aerobic & anaerobic metabolism during exercise

• lactate is generated and accumulated during usage of glucose and glycogen

• can be depleted 1 hour or less

Glycogen in liver

• reservoir of glucose when dietary glucose is not available

• depleted in 12-24 hours if not replenished

In liver and skeletal muscles, glucose units of outer branches enter glycolytic pathway via action of…

1. glycogen phosphorylase

2. glycogen debranching enzyme

3. phophoglucomutase

glycogen phosphorylase

• removes terminal glucose residues, from the nonreducing end, until 4 glucose residues away from branch point

• produces glucose-1-phosphate (G1P), which CANNOT enter glycolysis

glycogen debranching enzyme

• transfers 3 glucose units to a straight chain

• 1 free glucose residue is released and can enter glycolysis

phosphoglucomutase

• converts G1P to G6P

• G6P can then enter glycolysis, PPP or replenish blood glucose

Glycogen synthesis properties

• takes place in all animal tissues

• mostly in liver & skeletal muscles

• starting point: glucose-6-phosphate (G6P)

steps of glycogen synthesis

1. G6P converted to G1P by phosphoglucomutase

2. G1P converted to UDP-glucose

3. Glycogen chain elongated by glycogen synthase

4. Glucose residue transferred to nonreducing end of glycogen chain, UDP is released

5. Glycogen-branching enzymes

   • removes 6-7 sugars from a branch of at least 11 sugars long

   • new branch point is 4 sugars away from existing branch point