Glycogen metabolism

Question 1

Where is glycogen mainly found?

Answer 1

Liver and muscle

Question 2

What prevents muscle glycogen from being used as a source of glucose for the body?

Answer 2

Lack of glucose-6-phosphatase

Question 3

What are the major enzymes of glycogenesis?

Answer 3

Glycogen synthase
Branching enzyme

Question 4

What are the two options needed to start the chain of glycogen?

Answer 4

UDP-glucose as a primer
Glycogenin

Question 5

How does the branching enzyme work?

Answer 5

Removes 6-8 glucosyl residues from a chain of 10-11 and reattaches it by an alpha(1–>6) linkage

Question 6

How does G6P become the G1P used in glycogenesis?

Answer 6

Phosphoglucomutase

Question 7

How does G1P become UDP glucose used by glycogen synthase?

Answer 7

UDPG pyrophosphorylase using UTP and producing PPi

Question 8

What are the major enzymes of glycogenolysis?

Answer 8

Glycogen phosphorylase
Debranching enzyme

Question 9

What are the 2 enzymatic subunits of the debranching enzyme?

Answer 9

Oligo (1-4) to (1-4) glucan transferase
Amylo (1-6) glucosidase

Question 10

What is the coenzyme required by glycogen phosphorylase?

Answer 10

PLP

Question 11

How many residues remain before a branch after glycogen phosphorylase is finished?

Answer 11

4

Question 12

What is the main product of glycogenolysis?

Answer 12

Glucose-1P

Question 12

What is the function of the debranching enzyme?

Answer 12

Removes three glucosyl residues and reattaches them to main chain.
Cleaves (1-6) bond freeing last glucose-1P

Question 13

What disease is characterized by accumulation of glycogen in lysosomes?

Answer 13

GSD type II - Pompe disease

Question 14

What is the deficiency seen in Pompe disease?

Answer 14

acid maltase deficiency

Question 15

How does phosphorylation affect glycogen synthase?

Answer 15

Inactivates it

Question 16

How does phosphorylation affect glycogen phosphorylase?

Answer 16

Activates it

Question 17

How does insulin regulate glycogenesis?

Answer 17

Promotes dephosphorylation of glycogen synthase by decreasing cAMP by activating phosphodiesterase

Question 18

How do glucagon and epinephrine inhibit glycogenesis?

Answer 18

Promote phosphorylation of glycogen synthase by increasing cAMP by activating adenylate cyclase

Question 19

What promotes glycogenolysis in muscles?

Answer 19

Epinephrine only

Question 20

How does calcium influence glycogen metabolism?

Answer 20

Released by nerve impulses during muscle contraction. It will bind with calmodulin that activates muscle phosphorylase kinase, thereby activating glycogen phosphorylase

Increases glycogenolysis in muscles

Question 21

What are the inheritances patterns for GSDs I - VI?

Answer 21

Autosomal recessive

Question 22

What enzyme is deficient in Von Gierke’s disease (GSD Ia)?

Answer 22

Glucose-6-phosphatase

Question 23

What enzyme is deficienct in Cori disease (GSD III)?

Answer 23

Debranching enzyme

Question 24

What enzyme is deficient in Anderson disease (GSD IV)?

Answer 24

Branching enzyme

Question 25

What enzyme is deficient in McArdle disease (GSD V)?

Answer 25

Muscle phosphorylase

Question 26

What enzyme is deficient in Hers' disease (GSD VI)?

Answer 26

Hepatic glycogen phosphorylase

Question 27

What enzyme is deficient in GSD Ib?

Answer 27

Glucose-6P translocase

Question 28

What are the signs of Von Gierke's disease?

Answer 28

Hepato- and reno-megaly Fasting hypoglycemia Severe lactic acidemia - affects Cori cycle Ketosis Hyperlipidemia Fatty liver Hyperuricemia

Question 29

What are physical features in children with Von Gierke's disease?

Answer 29

Doll-like face Protruding abdomen

Question 30

What is the most severe GSD?

Answer 30

Pompe disease - type II

Question 31

What are signs of Pompe disease in children?

Answer 31

Muscle hypotonia Muscle weakness Death from cardiac failure by age 2

Question 32

What are signs of Pompe disease in adults?

Answer 32

Muscle dystrophy

Question 33

What are signs of Cori disease?

Answer 33

Fasting hypoglycemia Hepatomegaly in infants Accumulation of abnormal glycogen with shorter then normal branches

Question 34

What are other names for Cori disease (GSD III)?

Answer 34

Forbe disease Limit dextrinosis

Question 35

What are signs of Anderson disease?

Answer 35

Accumulation of abnormal glycogen with few branch points and longer branches Hepatosplenomegaly Death from heart or liver failure by 2

Question 36

What are signs of McArdle syndrome?

Answer 36

Poor exercise tolerance - muscle cramping and early fatigue Normal liver enzymes No rise in blood lactate after exercises Glycogen with normal structure accumulation in muscles Myoglobinemia Myoglobinuria