Glucose 6-phosphate to a longer glycogen chain, through glucose 1-phosphate and UDP-glucose
Route: Glucose 6-phosphate → Glucose 1-phosphate → UDP-Glc + Glycogen chain end (maltose stand-in) → Glycogen chain end plus one glucose (maltotriose stand-in)
Liver and muscle store glucose as glycogen, a branched polymer. Phosphoglucomutase turns glucose 6-phosphate into glucose 1-phosphate. UDP-glucose pyrophosphorylase joins glucose 1-phosphate to UTP and releases pyrophosphate. The cell splits the pyrophosphate with a pyrophosphatase, which pulls the reaction forward. UDP-glucose is the activated form of glucose. Glycogen synthase moves the glucose from UDP-glucose onto carbon 4 of the last glucose unit of a chain, which makes an alpha-1,4 bond and releases UDP. The drawing uses maltose for the end of a chain and maltotriose for the same end one glucose unit longer. A real chain has many more units. Glycogen synthase can only extend a chain of at least four glucose units, so a protein called glycogenin starts each molecule: it attaches glucose units to one of its own tyrosine residues until the chain is 10 to 20 units long. A branching enzyme makes the alpha-1,6 bonds at the branch points; it is not drawn here. In humans the structure shown is the muscle form of glycogen synthase; the liver has its own form.
Practice this pathway All pathways
| Step | Enzyme | EC | In | Out |
|---|---|---|---|---|
| 1 | Phosphoglucomutase | 5.4.2.2 | ||
| 2 | UDP-glucose pyrophosphorylase | 2.7.7.9 | UTP | PPᵢ |
| 3 | Glycogen synthase | 2.4.1.11 | UDP |
Build any of these from its atoms.
Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).