Glycogen storage diseases

Question 1

What is the necessary intermediate that glucose must form in order to be stored as glycogen?

Answer 1

UPD glucose

Question 2

What is the necessary position of a phosphate bond in order for a sugar to be converted to a UPD sugar

Answer 2

1-P

Question 3

Describe glycogen synthesis

Answer 3

Glycogen consists of molecules of glu that form lines and branches. Glycogen synthase connects glu in a serial manner (a1,4 bonds) and, when a branch is needed, the branching enzyme connects two glu moleculles with an a1,6 bond. Glycogen synthase deficiency will result in fasting hypoglycemia with ketosis (as with all glycogen storage or glyconeogenesis problems) BUT with the difference of POST-PRANDIAL LACTIC ACIDOSIS INSTEAD OF FASTING.

Question 4

What regulates glycogen synthase?

Answer 4

Insulin upregulates it via dephopshorylation. Glycagon does the opposite.

Question 5

Describe glycogenolysis

Answer 5

Glycogen phosphorylase breaks a1,4 bonds. When 4 glu molecules (or 4 limitr dextrins) remain in a branch, debranching enzyme moves the 3 glu molecules to the linkage and breaks the a 1,6 bond liberating the limit dextrin. Debranching enzyme definiency is seen in Cori (GS3). ONLY IN LYSOSOMES this whole process is done by one enzyme (acid maltase). Acid maltase deficiency gives rise to Pompe’s disease.

Question 6

What is the reqiured modification for glucose produced from glycogenolysis in order to be released and be used from other tissues?

Answer 6

6-P to be removed. Deficiency of G6 phosphatase causes Von Gierke’s Diseasee (GS1)

Question 7

Only liver synthesizes and stores glycogen?

Answer 7

This is also done by muscle. The difference is that the muscle breaks down glu only for its own use and DOES not contribute to serum glucose because it lack G6 phosphatase.
A lack of muscle phosphorylase is termed McArdle’s disease (GS5)