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Glycogen synthesis and breakdown

Q: How does debranching of glycogen work?

Debranching enzyme is a bifuntional enzyme , with both transferase activity and alfa-(1,6)-glycosidase activity Phosphorylase transferase (remodeling) alfa-(1,6)-glycosidase (debranching)

4 important questions on Glycogen synthesis and breakdown

How is a glucose added to a glycogen chain?

GS adds glucose at the non reducing end

Glucose 1-phosphate + UTP → UDP-glucose
UDP-Glucose + glucose[n] → Glucose[n+1]
Glycogen synthase (GS)
UDP out

How many ATP equivalents are required to add one glucose residue from blood to glycogen?

2 ATP to recycle UDP

How is Glucose 1-phosphate converted back to glucose after broken down form glycogen?

Glucose 1-phosphate needs to be converted into Glucose 6-phosphate which then produces free glucose (kindey and liver by glucose 6-phosphatase). Glucose 6-phosphatease is localized in the membrane of the ER, where glucose 6-phosphate is hydrolysed into glucose + Pi