Glycogen Metabolism

Question 1

Epinephrie

Answer 1

Stimulates glycogenolysis

Question 2

Purpose of glycogen metabolism

Answer 2

Rapid synthesis of glycogen when glucose 6-P is abundant [high blood insulin levels, both liver and muscle]

Rapid degradation of glycogen when glucose 6-P is needed[low insulin/glucagon ratio in liver, muscle contraction in muscle]

Question 3

phosphoglucomutase

Answer 3

reversibly converts glucose 6 P and glucose 1 P for glycogen degredation and synthesis.

Question 4

UDP-glucose

Answer 4

highly activated form of glucose which is used for synthesis of glycogen or other glycosylations

Glucose 1-P and UTP are used in an irreversible reaction and UDP-glucose and PPi are formed.

Enzyme: UDP-glucose pyrophosphrylase

Question 5

Glycogenin

Answer 5

a self-glucosylating enzyme that uses UDP-glucose and adds about 8 glucose units in tandem to its own tyrosine residue.

used in forming a new glygogen unit

After that, glycogen synthaseis able to form alpha-1,4 bonds at the non-reducing ends.

The branching enzyme forms the alpha-1,6 bond

Question 6

Hormonal regulation of glycogen synthase

Answer 6

Glycogen synthase A is the active form which is not phosphorylated.

High insulin levels activate protein phosphatase1 which cleave the phosphate from glycogen synthase B

Glucagon and epinephrine lead to the formation of the inactive phosphorylated glycogen synthaseB using protein kinaseA

Question 7

Limit Dextrin

Answer 7

intermediate in glycogen degradation

Branching chains with 4 residues left after initial phosphorylase action.

Substrate for the debranching enzyme

Question 8

Debranching enzyme

Answer 8

first activity is 4:4 transferase which leads from limit dextrin to longer branches

second activity is 1:6 glucosidase which cleaves the alpha-1,6 bond at the branch point and generates one molecule of free glucose

Question 9

Branching enzyme

Answer 9

Removes a chain of 6-8 glucosyl residues from the nonreducing end by cleavage of an alpha-1,6 bond and attaches it to a non-terminal glucosyl residue by an alpha 1,6 linkage

Question 10

Lysosomal acid glucosidase

Answer 10

Needed in lysosomes for glycogen breakdown

Question 11

Von Gierke Disease

Answer 11

Glycogen storage disease Type 1

Deficiency in Glucose 6 phosphatase

25% of glycogen storage disorders

Characterized by Severe hypoglycemia, hepatomegaly, kidney disease,

Treated with uncooked corn starch or gastric glucose infusion

Question 12

Pompe Disease

Answer 12

Glycogen storage disease Type 2

Lysosomal glucosidase deficiency

15% of glycogen storage disorders

Characterized by Massive cardiomegaly

Treatable with enzyme infusion

Question 13

Cori Disease

Answer 13

Glycogen storage disease type 3

Deficiency in debranching enzyme

24% of glycogen storage diseases

Characterized by mild hypoglycemia cardiomyopathy, muscular dystrophy hepatomegaly

Question 14

Andersen Disease

Answer 14

Glycogen storage disease type 4

Deficiency in branching enzyme

3% of glycogen storage diseases

Characterized by hepatomegaly due to cirrhosis, infintile hypotonia

Question 15

McArdle Syndrome

Answer 15

Glycogen storage disease type 5

Muscle glycogen phosphorylase deficiency

2% of glycogen storage diseases

characterized by muscle weakness and cramping, no increase of lactic acid in blood after exercise, lack of ATP, normal blood glucose levels

Question 16

Hers Disease

Answer 16

Glycogen storage type 6

Liver glycogen phosphorylase deficiency

30% of glycogen storage diseases

Characterized by mild hypoglycimia, hepatomegaly and growth retardation

Question 17

Tarui Disease

Answer 17

Glycogen storage disease typy 7

Deficiency in Phosphofructokinase 1

0.2% of glycogen storage diseases

Characterized by muscle weakness, cramping, no lactic acid in blood following exercise and Hemolysis of RBCs.