Question

Using circles to depict glucoses, draw a glycogen molecule with a main branch containing 12 glucose monomers. From the 5th glucose starting from the reducing end, draw a branch with 6 glucose monomers (Total 18 glucose monomers).

b)) Consider a liver cell with a debranching enzyme that lacks the ability hydrolyze 1,6 glycosidic linkages (it still has its other activity; all other enzymes are also working correctly). If this cell digests the above glycogen molecule, what would the products of this digestion look like? Draw the structure using circles to depict glucoses.

Answer 1

Glycogen is a branched polysaccharides, has 1- 4 bond in linear chain . This has alpha 1- 6 bond at braching point. Glycogen is initially degraded by glycogen phosphorylase, which release glucose in form of glucose 1 phosphate until p there are 4 glucose molecules remain each side of branching point. At this point this molecule is known as limit dextran. Further this limit dextrin, degrade by debranching enzyme (has both activity alpha 1- 4 transferae and 1- 6 glucocidase activity)

Alpha 4-4 transferase , transfer glucose molecules from branch to the linear chain.

Alpha 1- 6 glucocidase cleave remaining 1- 6 bond and release pure glucose . Again molecules undergo degradation from inital process.

If debranching enzyme 1-6 glycosidic activity lost than it will lead to accumulation of compound having one glucose molecule attached at branching point. And further degradation of molecule will stop.

To make understand in easy way , I have attached whole mechanism as attached image below . Hope this will help