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Biochemistry > Chapter 11 - glycogen synthesis and glycogenolysis > Flashcards

Chapter 11 - glycogen synthesis and glycogenolysis Flashcards

1
Q

What is glucose an energy source for?

A 
Brain
Cells lacking a mitochondria like RBCs
Cells with few mitochondria
Exercising muscles 
Sudden and strenuous activity
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2
Q

Where can blood glucose be obtained from?

A

Diet
Gluconeogenesis
Degradation of glycogen (glycogenolysis)

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3
Q

How can glucose be stored for later use?

A

as glycogen

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4
Q

Where does glycogen storage occur?

A

Liver and in skeletal muscle

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5
Q

TF: Most cells store small amounts of glycogen for own use?

A

True

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6
Q

Where does glycogen degradation and synthesis occur in the cell/

A

Cytosol

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7
Q

From what can glycogen be made?

A

Excess blood glucose

Recycling glucogenic metabolites (lactate, glycerol, amino acids)

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8
Q

What is the function of glycogen stores in the muscle?

A

Serve as a fuel reserve for synthesis of ATP

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9
Q

When are muscle glycogen stores replinished?

A

After depletion by strenuous exercise

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10
Q

What happens when glycogen stores are totally used up in the muscles but you still need more ATP?

A

Proteins are degraded to Amino Acids that can enter gluconeogenesis

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11
Q

What are the functions of glycogen stores in the liver?

A

Maintain blood glucose concentration for 10-18 hours at a time (nocturnal fasting)

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12
Q

What happens in the liver during the well fed state and during fasting?

A

When well fed, glycogen storage increases

When fasting they are depleted

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13
Q

How does glycogen exist in the cytoplasm?

A

As granules

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14
Q

What does the core complexes of glycogen consist of?

A

Glycogenin protein

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15
Q

What end is the non reducing end in glucose?

A

C4

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16
Q

How many non reducing ends are in glycogen?

A

Around 2000

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17
Q

What is the relationship between branch points and terminal residues for glycogen?

A

The more branch points, the more terminal residues are available at one time

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18
Q

What makes it possible for glycogen to release several glucose residues at once?

A

Highly branched structure of glycogen

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19
Q

What does glycogen produce in muscles?

A

G6P

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20
Q

What joins each alpha (OH below the ring) D glucose in glycogen?

A

alpha-1,4 glycosidic bonds

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21
Q

How often do branch points occur in glycogen and how are they joined?

A

Every 8-10 glucosyl residues

Joined by alpha-1,6 glycosidic bonds

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22
Q

What are the three steps of glycogen degradation?

A

Release of Glucose 1 phosphate from glycogen
Remodeling of glycogen for continued degradation
Conversion of glucose 1 phosphate into glucose 6 phosphate

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23
Q

What does each residue cleaved from glycogen react with?

A

Phosphate to give G1P

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24
Q

What kind of reaction cleaves glucose of from glycogen?

A

Phosphorolysis (glycogen phosphorylase)

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25
Q

What does glycogen phosphorylase do?

A

Cleaves the alpha 1,4 linkages in the non reducing ends of glycogen

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26
Q

Do you need ATP for the cleavage of glycogen?

A

No

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27
Q

How are branch points removed?

A

By 2 enzymatic activities in a single enzyme
Debranching enzyme that transfers a block of three residues to the non-reducing end of the chain
Debranching enzyme cleaves the single remaining alpha 1,6 linked glucose (becomes a free glucose)

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28
Q

What does phosphoglucomutase do?

A

Mutases transfer a side chain group throughout the same molecule
In this case the mutase is moving the phosphate from C1 to C6

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29
Q

What happens to G6P?

A

It is hydrolyzed by glucose 6 phosphotase (dephosphorylated) to release glucose

30
Q

Where does Glucose and Pi go after being released?

A

They are shuttled back to the cytoplasm by transporters

31
Q

What does liver glycogen phosphorylase do?

A

Breaks down glycogen into glucose 1 phosphate

32
Q

What does muscle glycogen phosphorylase do?

A

Breaks down glycogen to glucose 1 phosphate in the muscle

33
Q

What do muscle cells lack?

A

Glucose 6 phosphatase

34
Q

Where does glucose 6 phosphate go in the muscle cells since it cannot be dephosphorylated there?

A

Enters the glycolytic pathway directly and this saves 1 ATP

35
Q

What are the 3 fates of G6P?

A

Processing by the glycolytic pathway
Conversion into free glucose for release into the blood (only in liver)
Processing by the PPP

36
Q

Where does glycogen synthesis occur in the cell?

A

Cytosol

37
Q

TF: glycogen synthesis requires less energy than glycogen breakdown

A

False

38
Q

What must blood glucose be in order to synthesize glycogen?

A

Phosphorylated
Attached to UDP
Added to glycogen

39
Q

Why are there multiple steps for glycogen synthesis?

A

To allow for multiple points of regluation

40
Q

What is the first step for glycogen synthesis?

A

Glucose 6P is converted to glucose 1 P by phosphoglucomutase (transfers phosphate group)

41
Q

Where does the energy needed come from for glycogen synthesis?

A

Hydrolysis of UTP

42
Q

What is the second step for glycogen synthesis? (Stage 1)

A

Glucose 1P reacts with UTP to produce Uridine diphosphate glucose and pyrophosphate

43
Q

What does UDP glucose pyrophosphorylase do?

A

Catalyzes the interaction of G1P and UTP

44
Q

What does purophohatase do?

A

hydrolyzes PPi to Pi and PI

45
Q

What happens in stage 2 of glycogen synthesis?

A

UDPG is added to growing chain of glycogen (creates a new alpha 1,4 glycosidic bond that is catalyzed by glycogen synthase)

46
Q

When is UDP released from UDP glucose?

A

When the new alpha 1,4 glycosidic bond is formed on the nonreducing (C4) end of the already existing glycogen

47
Q

Where is the alpha 1,4 glycosidic bond formed in glycogen synthesis?

A

On the hydroxyl group of the anomeric carbon of the new glucose and the C4 non reducing end of the already existing glycogen

48
Q

What regenerates UDP to UTP?

A

UDP and ATP are used to make UTP by nucleoside diphosphate kinase

49
Q

What is the primer for glycogen?

A

Polysaccharide of glucose

50
Q

How is the primer for glycogen synthase made?

A

Glycogenin enzyme that is a dimer of two identical subunits

51
Q

What does each subunit of glycogenin generate?

A

a polysaccharide of 10-14 glucose residues in length

52
Q

What extends the primer?

A

Glycogen synthase

53
Q

What does a branching enzyme do?

A

Catalyses the reactions needed to introduce a branch point during the synthesis of glycogen

54
Q

How does the branching enzyme introduce branch points during synthesis of glycogen?

A

Transferring a segment (7 residues long) from the end of a growing chain to the branch point where it catalyzes the formation of the alpha 2,6 glycosidic linkage

55
Q

Where does the alpha 1,6 glycosidic linkage occur in glycogen?

A

At least 4 residues away from the previous branch point

56
Q

What extends branch points?

A

Glycogen synthase

57
Q

What is a major controlling factor in synthesis and breakdown of glycogen?

A

Glycogen phosphorylase

58
Q

What is glycogen phosphorylase subjected to for control?

A

Allosteric control and covalent modification

59
Q

What leads to activation of glycogen phosphorylase?

A

Phosphorylation of enzyme

60
Q

What leads to inhibition of glycogen phosphorylase?

A

Dephosphorylation of enzyme

61
Q

How is phosphorylation of glycogen phosphorylase controlled?

A

By the hormones Epinephrine and glucagon (activates breakdown of glycogen)

62
Q

What does phosphorylation do to glycogen synthase?

A

Inactivate it

63
Q

What does dephosphorylation of glycogen synthase cause?

A

Activation of the enzyme

64
Q

What is phosphorylation of glycogen synthase controlled by?

A

Stimulated by hormone signals of glucagon and epinephrine via the enzyme cAMP-dependent protein kinase

65
Q

What allosterically inhibits glycogen phosphorylase?

A

ATP and glucose 6 phosphate

66
Q

What inhibits glycogen phosphorylase in the liver?

A

Glucose

67
Q

What activates muscle glycogen phosphorylase?

A

Calcium ion release

68
Q

What activates glycogen phosphorylase?

A

AMP increase

69
Q

What allosterically activates glycogen synthase?

A

Elevated levels of glucose 6 phosphate

70
Q

What does the insulin signaling pathway do?

A

Increases glucose import into the liver
Activates glycogen synthase (dephosphorylation) - increase glucose synthesis
Inactivates glycogen phosphorylase (dephosphorylation)

71
Q

What does the glucagon-signaling pathway do?

A

Increases glucose export from liver
Activates glycogen phosphorylase (phosphorylation)- increases glycogen degredation
Deactivates glycogen sythase (phosphorylation)

Biochemistry (10 decks)

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