Mitsouras: Glycogenolysis

Front 1

What regulates synthesis and degradation of glycogen?

Back 1

1. Metabolic state
2. Exercise

Front 2

When does glycogen synthesis occur?

Back 2

Fed state

Front 3

When does glycogen degradation in muscle occur?

Back 3

Exercise

Front 4

When does glycogen degradation in the liver occur?

Back 4

Fasting

Front 5

What does glycogenolysis help prevent?

Back 5

hypoglycemia

Front 6

How is glycogen broken down?

Back 6

Sequential removal of glucose residues from the non-reducing ends

Front 7

What side of the glycogen molecule are the glucose residues removed?

Back 7

non-reducing end

Front 8

What enzyme breaks the alpha(1,4) bonds?

Back 8

Glycogen phosphorylase

Front 9

What enzyme breaks the alpha (1,6) bonds?

Back 9

Debranching enzyme

Front 10

What does glycogen phosphorylase produce?

Back 10

Glucose 1P

Front 11

How much of glycogen is glucose 1P?

Back 11

92%

Front 12

What does debranching enzyme produce?

Back 12

Glucose

Front 13

How much of glycogen is glucose?

Back 13

8%

Front 14

Which bond undergoes phosphorolysis?

Back 14

the alpha(1,4) bond

Front 15

What enzyme converts glucose 6P to glucose 1P, or visa versa?

Back 15

phosphoglucomutase

Front 16

What does high levels of glucose 6P activate?

Back 16

Glycogenesis

Front 17

What do high levels of glucose 1P do?

Back 17

drive the reaction toward glucose 6P and eventually glucose (once it is acted on by glucose 6-phosphatase)

Front 18

Where is glucose 6P found?

Back 18

ONLY IN THE LIVER

Front 19

What is glucose 6P used for?

Back 19

Gluconeogenesis, glycogenolysis

Front 20

What type of cleavage is used to break the alpha (1,4) bonds? What does that mean?

Back 20

Phosphorolytic cleavage, means it requires Pi for the glycogen phosphatase to work

Front 21

What is the product of the alpha (1,4) bond cleavage?

Back 21

glucose 1P

Front 22

What cofactor is required for glycogen phosphatase?

Back 22

Pyridoxal phosphate (PLP)

Front 23

When does glycogen phosphatase stop working on the linear portion of a branch?

Back 23

Stops at 4 glucoses from branch point

Front 24

How does debranching enzyme work?

Back 24

1. 3 glucose residues are transferred from branch to non-reducing end of glycogen chain
2. Hydrolysis of alpha (1,6) bond

Front 25

What is the product of the alpha (1,6) bond cleavage?

Back 25

Glucose

Front 26

How is glycogenolysis hormonally regulated?

Back 26

Glucagon activates protein kinase A, which phosphoryllates phosphorylase kinase, turining it on, phosphorylating glycogen phosphorylase, turning it on, and turning glycogenelysis on

Front 27

What are the allosterics regulators of glycogenolysis?

Back 27

ATP, Glucose, Glucose 6P turn glycogen phosphorylase OFF

Front 28

How does insulin regulate glycogenolysis?

Back 28

Insulin activates protein phosphatase 1, which dephosphorylates glycogen phosphorylase, turning it off, and turning glycogenolysis off
Protein phosphatase 1 also dephosphorylates phosphorylase kinase, turning it off, which turns glycogen phosphorylase off and glycogenolysis off

Front 29

Does muscle respond to glucagon?

Back 29

No

Front 30

What stimulates glycogenolysis in muscle?

Back 30

exercise

Front 31

What regulates glycogenolysis in muscle?

Back 31

1. Epinephrine and Ca2+ turn glycogen phosphorylase on
2. AMP is an allosteric activator of glycogen phosphorylase, turning it on

Front 32

What are the enzymes influenced by glycogen storage diseases?

Back 32

1. glucose 6phosphatase
2. debranching enzyme
3. branching enzyme
4. glycogen phosphorylase
5. phosphofructokinase
6. phosphorylase kinase
7. glycogen synthasse

Front 33

What are the symptoms of a debranching enzyme deficiency?

Back 33

Hypoglycemia, hepatomegaly (liver)

Front 34

What are the symptoms of glycogen phosphorylase deficiency?

Back 34

1. Muscle fatigue and cramping (muscles)
2. Hepatomegaly, hypoglycemia (liver)

Front 35

What are the symptoms of glucose-6-phosphatase deficiency?

Back 35

ONLY IN THE LIVER
Hypoglycemia, hepatomegaly

Front 36

What are the symptoms of phosphofructokinase deficiency?

Back 36

Phosphofructokinase is used to oxidize Glucose 6P in muscle and a deficiency will produce fatigue and muscle cramps

Front 37

What is the result in a branching enzyme deficiency?

Back 37

No glycogen formation, would cause hyperglycemia and hepatomegaly (both in the liver)

Front 38

What is Von Gierke's disease?

Back 38

Type I
Deficiency of Glucose-6 Phosphatase

*fasting hypoglycemia, sever hepatomegaly, ketosis
cannot convert glucose 6P to glucose which would signal less glycogenolysis

Front 39

What is Pompe's disease?

Back 39

Type II
Deficiency in alpha-1,4 glucosidase

Affects all organs
Infant form: death by 2 y.o., hypotonia, mental retardation, cardiomegally
Adult form: gradual skeletal myopathy

Front 40

What is Cori/Forbes disease?

Back 40

Type III
Deficiency in debranching enzyme

Affects muscle and liver

Would cause mild hypoglycemia and hepatomegaly

Front 41

What is Andersen's disease?

Back 41

Deficiency in branching enzyme
Type IV
Affects the liver

Causes hepatomegally, cirrhosis, liver failure, death by 2 yo
Problem bc glycogen has very few branches

Front 42

What is McArdle's disease?

Back 42

Type V
Deficiency is glycogen phosphorylase in the MUSCLE

Affects the muscle

Would cause increased amount of glycogen bc not being broken down

Result is muscle cramps, fatigue

Front 43

What is Her's disease?

Back 43

Type VI
Glycogen phosphorylase deficiency in the LIVER

Affect the liver

Increased glycogen bc cannot be broken down
Results in fasting hypoglycemia, ketosis, hepatomegaly (less severe than Von Gierke's)

Front 44

What is Tarui's disease?

Back 44

Type VII
Phosphofructokinase deficiency in the MUSCLE

Results in increased glycogen and muscle fatigue and cramping

Front 45

What is Type VIII glycogen storage deficiency?

Back 45

Phosphorylase kinase deficienvy in the LIVER

Results in hepatomegaly and hypoglycemia bc problem with glycogen breakdown