Glycogenolysis

Question 1

Step 1

Answer 1

Glucagon & epinephrine bind to receptors on the cell surface; triggers signaling cascade that activates protein kinase A (PKA)

Question 2

PKA Signaling Cascade

Answer 2

PKA phosphorylates & activates phosphorylase kinase which then activates glycogen phosphorylase

Question 3

Step 2

Answer 3

Activated glycogen phosphorylase acts on α-1,4 glycosidic linkages between glucose molecules

Removes glucose residues one by one, releasing glucose-1-phosphate

Question 4

Step 3

Answer 4

Glucan transferase (amylo-(1,4→1,6)-transglycosylase) relocates fragments from
chain to a branch point allowing new place to break down glycogen

Question 5

Step 4

Answer 5

Relocation of fragments exposes branch point containing α-1,6-glycosidic bond
Debranching enzyme (glycogen-debranching enzyme) hydrolyzes the α-1,6-glycosidic bond, releasing a free glucose molecule

Question 6

Isomerization

Answer 6

Glucose 1-phosphate isomerized to glucose 6-phosphate by phosphoglucomutase, then Glucose 6-phosphatase dephosphorylates, producing glucose.

Question 7

Liver isomerization

Answer 7

glucose 6-phosphate transported to endoplasmic reticulum (ER) by glucose 6-phosphate translocase

Question 8

Blood Glucose Level

Answer 8

Hepatocytes release glycogen-derived glucose into circulation to help maintain blood glucose levels

Question 9

Muscle Exception

Answer 9

*Muscle lacks glucose 6-phosphatase; traps glucose 6-phosphate for use in glycolysis