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BMS 610 Exam 3 > Chapter 15 - Glycogen Metabolism & Regulation > Flashcards

Chapter 15 - Glycogen Metabolism & Regulation Flashcards

1
Q

What is glycogen, and where is it primarily stored in animals?

A

A polymeric form of glucose stored mainly in the liver and muscle.

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2
Q

What is the difference between α- and β-granules in glycogen?

A

α-granules are larger clusters of β-granules, visible in the liver after feeding.

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3
Q

What is glycogenolysis?

A

The process of breaking down glycogen to glucose-1-phosphate.

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4
Q

Define glycogenesis.

A

The synthesis of glycogen from glucose.

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5
Q

Which enzyme catalyzes the breakdown of glycogen in glycogenolysis?

A

Glycogen phosphorylase.

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6
Q

What is the role of phosphoglucomutase in glycogen metabolism?

A

Converts glucose-1-phosphate to glucose-6-phosphate for glycolysis or release into the blood.

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7
Q

How does glycogen breakdown differ between muscle and liver?

A

In muscle, glucose-6-phosphate enters glycolysis; in liver, it can be converted to glucose to maintain blood sugar levels.

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8
Q

What is the role of UDP-glucose in glycogenesis?

A

It donates glucose units to extend the glycogen chain.

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9
Q

Describe the function of glycogenin in glycogen synthesis.

A

Acts as a primer for glycogen synthesis, catalyzing the addition of initial glucose residues.

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10
Q

How does glycogen phosphorylase regulation differ in muscle and liver?

A

In muscle, it responds to AMP and Ca²⁺ for energy demand; in liver, it responds to glucose and hormones like glucagon.

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11
Q

How is glycogen synthase regulated?

A

Activated by insulin and glucose-6-phosphate, inactivated by phosphorylation.

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12
Q

What role does cAMP play in glycogen breakdown?

A

Activates a cascade leading to glycogen phosphorylase activation, promoting glycogenolysis.

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13
Q

Explain the role of Ca²⁺ in muscle glycogenolysis.

A

Activates phosphorylase kinase, which then activates glycogen phosphorylase.

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14
Q

What effect does AMP have on glycogen phosphorylase in muscle?

A

Activates glycogen phosphorylase, increasing glucose release during high energy demand.

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15
Q

How does insulin influence glycogen synthesis?

A

Insulin activates glycogen synthase by inactivating GSK3 and increasing PP1 activity.

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16
Q

Describe the role of glucagon in glycogen metabolism in the liver.

A

Stimulates glycogen breakdown to increase blood glucose levels.

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17
Q

How does epinephrine affect glycogen metabolism in muscle?

A

Stimulates glycogen breakdown for rapid ATP production during ‘fight or flight’ response.

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18
Q

What is the effect of glucose on liver glycogen phosphorylase?

A

Glucose binding promotes dephosphorylation and inactivation of glycogen phosphorylase.

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19
Q

Describe the enzyme cascade activated by cAMP in glycogenolysis.

A

cAMP activates PKA, which activates phosphorylase kinase, leading to activation of glycogen phosphorylase.

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20
Q

What is the role of phosphoprotein phosphatase 1 (PP1) in glycogen metabolism?

A

PP1 dephosphorylates glycogen phosphorylase and glycogen synthase, modulating their activities.

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21
Q

Name a key allosteric inhibitor of muscle glycogen phosphorylase.

A

ATP, which signals sufficient energy and inhibits glycogen breakdown.

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22
Q

What is the difference in glycogen metabolism regulation between muscle and liver?

A

Muscle glycogen breakdown is for ATP, while liver glycogen regulates blood glucose levels.

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23
Q

Describe Type Ia glycogen storage disease and its cause.

A

Caused by glucose-6-phosphatase deficiency, leading to hypoglycemia and glycogen accumulation.

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24
Q

What is Type V glycogen storage disease (McArdle disease)?

A

Caused by muscle glycogen phosphorylase deficiency, resulting in exercise intolerance.

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25
Explain the role of GSK3 in glycogen metabolism.
GSK3 phosphorylates and inactivates glycogen synthase, inhibiting glycogenesis.
26
How does glucose-6-phosphate affect glycogen synthase?
Allosterically activates the inactive form, promoting glycogen synthesis.
27
Describe Pompe disease and its symptoms.
Caused by acid maltase deficiency, leading to glycogen accumulation in lysosomes and muscle weakness.
28
What triggers the activation of glycogen phosphorylase kinase in muscle?
Increased calcium levels during muscle contraction.
29
How does insulin inhibit GSK3?
Through signaling pathways that inactivate GSK3, promoting glycogen synthesis.
30
What is the effect of fasting on liver glycogen metabolism?
Fasting increases glucagon, stimulating glycogen breakdown to maintain blood glucose.
31
How does glycogen branching enzyme function in glycogenesis?
It creates α(1→6) branches, increasing glycogen solubility and energy release rate.
32
What is Cori disease (Type III glycogen storage disease)?
Caused by deficiency in debranching enzyme, leading to abnormal glycogen with short outer branches.
33
What causes Anderson disease (Type IV glycogen storage disease)?
Branching enzyme deficiency, resulting in abnormal, unbranched glycogen.
34
Describe the importance of glucose-6-phosphatase in liver glycogen metabolism.
Converts glucose-6-phosphate to free glucose for blood glucose regulation.
35
What enzyme deficiency causes Hers disease (Type VI)?
Liver glycogen phosphorylase deficiency, leading to mild hypoglycemia.
36
What role does casein kinase II (CKII) play in glycogen metabolism?
Primes glycogen synthase for phosphorylation by GSK3, regulating glycogenesis.
37
How does PP1 activity differ in response to insulin in muscle vs. liver?
PP1 is activated by insulin in both, but with a greater effect on liver glycogen synthesis.
38
What is the significance of AMP-activated protein kinase (AMPK) in muscle?
Activates energy production pathways, including glycogenolysis, during low energy states.
39
How does the liver sense glucose to regulate glycogen metabolism?
Glucose binds to phosphorylase, making it more susceptible to inactivation by PP1.
40
Why is glycogen a preferred storage form of glucose?
It is rapidly mobilizable, does not diffuse out of cells, and avoids osmotic issues.
41
How does glycogen synthase add glucose to glycogen?
Transfers glucose from UDP-glucose to the non-reducing end of glycogen.
42
Describe the autocatalytic function of glycogenin in glycogen synthesis.
Glycogenin catalyzes the addition of glucose residues to its own tyrosine residues, creating a primer for glycogen synthase.
43
How is glucose-1-phosphate formed from glucose-6-phosphate?
Through the action of phosphoglucomutase, which transfers a phosphate group.
44
Why is UDP-glucose formation considered irreversible?
The release and hydrolysis of pyrophosphate make the reaction energetically favorable.
45
What is the role of glucagon in hepatic glycogen metabolism during fasting?
Glucagon activates glycogenolysis, increasing blood glucose levels by promoting glycogen breakdown.
46
How does epinephrine signal glycogen breakdown in muscle?
It binds to β-adrenergic receptors, activating a cAMP cascade that activates glycogen phosphorylase.
47
Explain how AMP acts as an allosteric activator in muscle glycogenolysis.
AMP binds to glycogen phosphorylase, enhancing its activity to release glucose-1-phosphate during energy demand.
48
What initiates the inactivation of glycogen phosphorylase in liver cells?
Glucose binding exposes phosphorylated residues, making it a target for dephosphorylation by PP1.
49
Describe the role of phosphoglucomutase in glucose utilization.
Converts glucose-1-phosphate to glucose-6-phosphate for entry into glycolysis or conversion to free glucose in the liver.
50
How does insulin signaling activate glycogen synthase?
Insulin inhibits GSK3 and activates PP1, which dephosphorylates and activates glycogen synthase.
51
What is the role of branching enzyme deficiency in Anderson disease?
Lack of branching enzyme results in unbranched glycogen, which is poorly soluble and can lead to liver dysfunction.
52
Why does Cori disease result in abnormal glycogen structure?
A deficiency in debranching enzyme prevents full glycogen breakdown, creating glycogen with short outer branches.
53
How does glycogen synthase kinase 3 (GSK3) regulate glycogen synthase?
GSK3 phosphorylates glycogen synthase, converting it to an inactive form, thus inhibiting glycogen synthesis.
54
What is the function of liver glycogen phosphorylase during hypoglycemia?
It breaks down glycogen to maintain blood glucose levels, especially important during fasting.
55
What is McArdle disease, and what symptoms are associated with it?
McArdle disease is a muscle glycogen phosphorylase deficiency, leading to exercise intolerance and muscle pain.
56
How is glycogen metabolism regulated differently in liver and muscle tissue?
The liver controls blood glucose through glycogen metabolism, while muscle uses glycogen solely for its own energy needs.
57
What initiates the cascade effect in glycogen breakdown upon epinephrine binding?
Epinephrine binding increases cAMP, activating PKA, which activates phosphorylase kinase, leading to glycogen phosphorylase activation.
58
Why is ATP an inhibitor of glycogen phosphorylase in muscle?
High ATP indicates sufficient energy, thus inhibiting glycogen breakdown to conserve resources.
59
Describe the cascade effect of cAMP on glycogenolysis.
cAMP activates protein kinase A (PKA), which phosphorylates and activates phosphorylase kinase, ultimately activating glycogen phosphorylase.
60
How does PP1 facilitate the activation of glycogen synthase?
PP1 dephosphorylates glycogen synthase, converting it to its active form for glycogen synthesis.
61
What role does glucose play in the allosteric regulation of liver glycogen phosphorylase?
Glucose binding to liver glycogen phosphorylase induces a conformational change, making it more susceptible to inactivation by PP1.
62
Describe the role of protein kinase A (PKA) in glycogen metabolism.
PKA phosphorylates enzymes like phosphorylase kinase, initiating glycogenolysis, and inhibits glycogen synthase to prevent glycogenesis.
63
Why is insulin essential for glycogen synthesis?
Insulin promotes dephosphorylation of glycogen synthase, activating it to facilitate glucose storage.
64
How does calcium (Ca²⁺) enhance glycogen breakdown in muscle?
Ca²⁺ binds to phosphorylase kinase, activating it, which then activates glycogen phosphorylase for glycogenolysis during muscle contraction.
65
What genetic mutation causes Von Gierke disease (Type Ia)?
Mutation in glucose-6-phosphatase, leading to impaired blood glucose maintenance and hypoglycemia.
66
How does Type Ib glycogen storage disease differ from Type Ia?
Type Ib involves a defect in the glucose-6-phosphate transporter, while Type Ia is a glucose-6-phosphatase deficiency.
67
Explain how the liver regulates blood glucose via glycogen metabolism during fasting.
During fasting, glucagon activates glycogen breakdown in the liver, increasing glucose release into the bloodstream.
68
Describe the impact of phosphoprotein phosphatase 1 (PP1) on glycogen breakdown.
PP1 dephosphorylates glycogen phosphorylase, reducing its activity and slowing glycogenolysis.
69
How does fasting influence the action of glycogen phosphorylase in the liver?
Fasting increases glucagon, activating glycogen phosphorylase and promoting glycogen breakdown for blood glucose maintenance.
70
Why does muscle lack glucose-6-phosphatase, and how does this affect glycogen metabolism?
Muscle lacks glucose-6-phosphatase to retain glucose for its own use rather than releasing it into the blood.
71
What is the significance of glycogen branching in energy release?
Branching increases the number of non-reducing ends, allowing rapid glucose release during glycogen breakdown.
72
How does liver glycogen metabolism respond to insulin and glucagon?
Insulin promotes glycogen synthesis, while glucagon stimulates glycogen breakdown for blood glucose maintenance.
73
What is the impact of glycogen storage diseases on metabolism?
They disrupt glycogen synthesis or breakdown, often leading to hypoglycemia, muscle weakness, or organ enlargement.
74
What enzyme deficiency causes Hers disease, and what are its effects?
Liver glycogen phosphorylase deficiency, resulting in mild hypoglycemia due to reduced glycogen breakdown in the liver.
75
Explain the role of debranching enzyme in glycogenolysis.
It removes branches by transferring glucose residues and hydrolyzing α(1→6) linkages, facilitating glycogen breakdown.

BMS 610 Exam 3 (4 decks)

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