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GI > Glycogen and GSD > Flashcards

Glycogen and GSD Flashcards

1
Q

An extended and branched polymer of glucose, with each granule having a molecular weight in excess of 2000 kDa

A

Glycogen

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2
Q

Glucose residues are joined in a linear chain by

A

a-1,4 glycosidic bonds

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3
Q

The branch points of glycogen, which occur, on average, every 10 or so residues, have an

A

a-1,6-glycosidic bond

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4
Q

Composed of very long linear polymers of glucose, but in a B-1,4 linkage

A

Cellulose

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5
Q

In plants, starch functions for energy storage, while cellulose has a

A

Structural role

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6
Q

Represents one of the two basic forms in which the chemical energy derived from foods is stored

A

Glycogen

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7
Q

The two largest reservoirs of glycogen in the body

A

Muscle and Liver

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8
Q

Mobilized in the early phases of a fast, in order to maintain blood glucose levels

A

Liver Glycogen stores

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9
Q

In most individuals, liver glycogen stores can meet this need for between

A

12-24 hours

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10
Q

CANNOT contribute to the maintenance of blood glucose levels, but instead are utilized as a site specific energy source

A

Muscle glycogen stores

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11
Q

The major intersection in the glucose metabolism road map

A

Glucose-6-phosphate

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12
Q

Converts glucose-6-phosphate to glucose-1-phosphate

A

Phosphoglucomutase

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13
Q

Glucose 1-phospate becomes the substrate for

-adds a UMP portion while releasing pyrophosphate (PPi)

A

UDP-glucose phosphorylase

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14
Q

The resultant UDP-glucose is the immediate precursor in glycogen polymer extension, carried out by

A

Glycogen Synthase

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15
Q

Polymerizes glucose residues by catalyzing the formation of the a-1,4-linkages

A

Glycogen synthase

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16
Q

Addition of each glucose residue is coincident with release of its

A

UDP carrier

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17
Q

Glycogen synthase cannot create branch structures, however. This task is the responsibility of the

A

Branching enzyme

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18
Q

NOT a substrate for this enzyme

A

UDP-glucose

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19
Q

Able to transfer a five- to eight-mer of a linear glycogen polymer to another glucose residue ‘upstream’ on the polymer chain, forming the alternative a-1,6 linkage

A

Branching Enzyme

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20
Q

This creates a new polymer growing end and thus an additional substrate upon which glycogen synthase can act to elongate the

A

Glycogen Chain

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21
Q

Cannot initiate polymer synthesis. It can only add to a pre-existing polymer

A

Glycogen Synthase

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22
Q

Has several critical roles in the initiation of glycogen synthesis

A

Glycogenin

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23
Q

The hydroxyl moiety of a tyrosine residue in glycogenin serves for the formation of the first

A

Glycosidic bond

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24
Q

Importantly, this first glucose residue is attached not by glycogen synthase but by an enzymatic activity in

A

Glycogenin

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25
Q

After the polymer is at least eight residues long, polymerization occurs via

A

Glycogen Synthase

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26
Q

Apart from the ATP that is required to phosphorylate free glucose, one additional ATP is required for each glucose residue added to the

A

Polymer

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27
Q

This ATP is consumed by

-carries out the reaction UDP + ATP –> UTP + ADP

A

Nucleoside diphosphate kinase

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28
Q

Echoing patterns in both glycolysis/gluconeogenesis and in fatty acid synthesis/B oxidation, glycogen breakdown is not simply the reverse of

A

Glycogen Synthesis

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29
Q

Not an intermediate in glycogen breakdown

A

UDP-Glucose

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30
Q

Importantly, it is in the breakdown of glycogen that the liver and muscle

A

Differ

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31
Q

Glycogen breakdown begins at the many branch ends of the molecule, with the action of

A

Glycogen Phosphorylase

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32
Q

Inorganic phosphate is recruited in this reaction, producing

A

Glucose-1-phosphate

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33
Q

Glucose 1-phosphate is subsequently isomerized to glucose 6-phosphate by

A

Phosphoglucomutase

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34
Q

The only enzyme the synthetic and degradative pathways share

A

Phosphoglucomutase

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35
Q

In analogy to glycogen synthase, glycogen phosphorylase cannot attack the

A

a-1,6-linkage at branch points

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36
Q

In fact, phosphorylase halts its progressive release of gluocse 1-phosphate molecules how many residues before a branch?

A

Four

37
Q

Branch removal is a 2-step process. The first step is catalyzed by the

A

Debranching enzyme (glucosyl (4:4) transferase)

38
Q

This enzyme transfers three of those four residues to another non-reducing end, in a single catalytic step, via conventional

A

a-1,4-linkages

39
Q

This leaves only one glucose residue in a

A

a-1,6-linkage

40
Q

The second step is catalyzed by amylo-(a-1,6)-glucosidase, which releases

A

Free glucose

41
Q

We will call this second enzymatic activity ‘debranching enzyme’ as well, because, in fact, both enzymatic activities dealing with breakdown of branch structures are present on

A

One polypeptide

42
Q

The result of glycogen mobilization in all tissues is the release, predominantly, of

A

Glucose-1-phosphate

43
Q

Able to remove the phosphate residue to liberate free glucose

A

Liver glucose-6-phosphatase

44
Q

Free glucose can in turn enter the circulation, thereby contributing to the maintenance of

A

Blood glucose

45
Q

In contrast, muscle lacks this phosphatase, so product gluose 6-phosphate is shunted directly into

A

Glycolysis for ATP production

46
Q

Remember that a modest quantity of free glucose is produced in muscle glycogen breakdown via the second step catalyzed by

A

De-branching enzyme

47
Q

While liver glycogen supplies serve to maintain blood glucose levels in the early stages of a fast, muscle glycogen does not, due to the absence of a muscle

A

Glucose-6-phosphatase

48
Q

What are the energy expenditures in mobilization of glycogen?

A

None

49
Q

Uses inorganic phosphate, not ATP, to produce glucose 1-phosphate

A

Glycogen phosphorylase

50
Q

The key enzymes targeted to regulate glycogen synthesis and breakdown are

A

Glycogen synthase and glycogen phosphorylase

51
Q

Hormonal regulation in the liver is mediated by

A

Insulin and glcucagon

52
Q

Hormonal regulation in the muscle is mediated by

A

Insulin and epinephrine

53
Q

Undergo covalent modifications that variously stimulate or inhibit their activity

A

Glycogen synthase and phosphorylase

54
Q

In exercising muscle, Ca2+ comes into play, and glycogen mobilization can reach very high rates in a matter of only a few

A

Seconds

55
Q

However, these changes can also be long lasting. Liver glycogenolysis is a process that may go on, uninterrupted, for

A

12 hours or more during fasting

56
Q

Contrasting the insulin/glucagon/epinephrine regulatory input is what we’ll call ‘local’ regulation via small molecule

A

Allosteric effectors

57
Q

During the early stages of a fast, and periods of muscle activity, the trend will be to

A

Activate the phosphorylase and inhibit the synthase

58
Q

For the energy poor state, what is the

  1. ) Hormonal signal?
  2. ) Intracellular signal?
A
  1. ) GLucagon

2. ) AMP

59
Q

Signal periods of muscle activity in skeletal muscle

A

Ca2+ and epinephrine

60
Q

The energy-poor hormonal signaling pathway in liver begins with the binding of glucagon to its

A

Membrane bound receptor

61
Q

The receptor activates an adenylate cyclase, causing an increase in intracellular

A

cAMP concentration

62
Q

cAMP in turn activates a

A

cAMP-dependent protein kinase

63
Q

Phosphorylates glycogen synthase-a, converting it to the inactive “b” form

A

cAMP-dependent protein kinase

64
Q

In fact, glycogen synthase is able to accept as many as

-number of phosphatases determines degree of inhibition

A

9 phosphatases

65
Q

This same cAMP-dependent protein kinase also activates a second protein kinase, known as

A

Phosphorylase kinase

66
Q

In turn is able to convert inactive glycogen phosphorylase-b to the active (phosphorylated) a form

A

Phosphorylase kinase

67
Q

The net effect is the shut down of glycogen synthesis and the activation of

A

Glycogenolysis

68
Q

Nervous stimulation of muscle includes membrane bound receptor binding of

A

Epinephrine

69
Q

Nervous stimulation of muscle includes binding of epinephrine to its membrane-bound receptors as well as the release of sarcoplasmic stores of

A

Ca2+

70
Q

Epinephrine’s stimulation of muscle glycogenolysis follows the cascade already described for

A

Glucagon

71
Q

Importantly, Ca++ binding to the calmodulin subunit of phosphorylase kinase stimulates its activity to phosphorylate

A

Glycogen phosphorylase

72
Q

This signaling can be done inthe absence of

A

cAMP

73
Q

As muscle relaxes, free intracellular Ca++ levels drop and the phosphorylase kinase is again deactivated by

A

Calmodulin

74
Q

Reverse the modifications made by phosphorylase kinase and the mobilization of glycogen halts once again

A

Cellular phosphatases

75
Q

On the local level, muscle glycogen phosphorylase is allosterically

  1. ) Activated by (indicator of energy defecit)?
  2. ) Inhibited by (indicator of energy abundance)?
A
  1. ) AMP

2. ) Phosphocreatine

76
Q

A good example of local regulation “trumping” hormonal regulation is shown here, where AMP can activate the

A

Unphosphorylated enzyme

77
Q

Conversely, the active, phosphorylated form can be locally inhibited by

A

ATP and Glucose-6-phosphate

78
Q

During energy-rich periods, and periods of muscle inactivity, the trend will be to

A

Activate the synthase and inhibit the phosphorylase

79
Q

What are the principal molecular signals of an energy rich state?

A

Insulin, G-6-P, Glucose, and ATP

80
Q

The energy-rich state is signaled by a high

A

Insulin to glucagon ratio

81
Q

Increasing this ratio stimulates glycogen synthesis over its

A

Degredation

82
Q

In liver and muscle, efficient insulin binding to its receptor activates a

A

Tyrosine Kinase

83
Q

This kinase in turn activates another kinase, whose ultimate target is

A

Protein Phosphatase 1 (PP1)

84
Q

Removes inhibitory phosphates from glycogen synthase (converting it back to the active “a” form), as well as removing the activating phosphate(s) from glycogen phosphorylase (converting it to the inactive “b” form)

A

PP1

85
Q

The net effect, therefore, of insulin signaling, is to

A

Activate glycogen synthase

Inhibit glycogen phosphorylase

86
Q

In terms of local allosteric regulation, high levels of glucose 6-phosphate, signaling an energy rich state, allosterically

A

Activate glycogen synthase and inhibit glycogen phosphorylase

87
Q

Is also able to inhibit glycogen phosphorylase

A

ATP

88
Q

These effects are largely independent of the phosphorylation state of glycogen synthetase, and thus constitute a parallel regulatory mechanism that operates on local and short-term scales and is able to override

A

Hormonal input

89
Q

There are atleast 9 different deficiencies in glycogen metabolism. These are referred to as

A

Glycogen storage diseases or Glycogenoses

GI (59 decks)

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