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Biochemistry > Glycogen Metabolism, Synthesis, and PPP > Flashcards

Glycogen Metabolism, Synthesis, and PPP Flashcards

1
Q

What is glycogen?

A

Glycogen is a polysaccharide consisting of a-1,4-linked glucose with a-1,6- branched glucose every ~ 10 residues.

Glycogen is a readily mobilized form of glucose that is stored mainly in liver and muscle.

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2
Q

What is the process that cleaves glycogen?

A

Phosphorolytic Cleavage

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3
Q

Does cleaving glycogen require ATP?

A

No

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4
Q

What is the final product after cleaving glycogen?

A

Glucose-1-Phosphate

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5
Q

Where does degredation of glycogen start?

A

non-reducing ends (free ends)

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6
Q

What is the first step of glycogen degradation?

What is the enzyme?

A

Phosphorolytic Cleavage

Glycogen Phosphorylase

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7
Q

What happens during Phosphorolytic Cleavage?

A

Glycogen Phosphorylase adds an inorganic phosphate to the non-reducing end of glycogen to form G-1-P. Resulting glycogen polymer is one unit shorter.

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8
Q

What happens to the G-1-P, and what enzyme is responsible?

A

Converted into G-6-P by Phosphoglucomutase

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9
Q

How does Phosphoglucomutase work?

A

This enzymes functions by covalently modifying a serine residue which exchanges phosphate w/ G-1-P to make a G-1,6-BP intermediate prior to a back exchange to the 6 position to make G-6-P

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10
Q

What happens to the G-6-P, and what enzyme is involved?

A

It gets converted into glucose by Glucose-6-Phosphatase

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11
Q

What are the two enzymes needed to deal with a-1,6 branching?

A

Transferase

a-1,6 Glucosidase

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12
Q

Where does this occur?

glycogen metabolism is used during heavy exercise for anaerobic respiration

G-6-P goes directly into glycolysis

A

Muscle

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13
Q

Where does this occur?

glycogen metabolism is designed for glucose export into blood

G-6-P must be converted to glucose for export

A

Liver

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14
Q

What is the function of transferase?

A

Removes three of the four residues left at the branch point by glycogen phosphorylase and catalyzes their polymerization onto the unbranched strand (a-1,4-linkages)

Removes them from branch and places them on the main line

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15
Q

What is the function of a-1,6-glucosidase?

A

Removes the final a-1,6 glucose from the branch

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16
Q

Regulation of glycogen metabolism occurs through ____.

A

Signal Transduction

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17
Q

Of Glycogen Phosphorylase A and Glycogen Phosphorylase B, which is active and which is inactive?

A

A is active and phosphorylated,

B is inactive and de-phosphorylated

Both have T and R states

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18
Q

How is Glycogen Phosphorylase A regulated?

A

The a form (which is nearly all in the R state) in muscle is regulated by phosphorylation/dephosphorylation of b to a

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19
Q

How is Glycogen Phosphorylase B regulated?

A

The b form is downregulated by ATP and G-6-P (conversion to T form) and upregulated by AMP (conversion to R form).

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20
Q

What is needed for glycogen synthesis?

A

A high energy intermediate glucose donor, uridine diphosphate glucose (UDP-glucose).

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21
Q

How is UDP-glucose formed?

A

From a reaction of UTP with G-1-P

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22
Q

What is the reaction that forms UDP-Glucose, and what is the enzyme involved?

A

UTP + G-1-P to UDP-G + PPi (pyrophosphate from UTP)

UDP glucose pyrophosphorylase

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23
Q

Is it possible to reverse the formation of UDP-Glucose? What causes this?

A

Reaction is made irreversible by inorganic pyrophosphatase that takes PPi to 2Pi

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24
Q

What Molecule is this?

A

Glucose

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25
Q

What Enzyme is this?

A

Hexokinase

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26
Q

What Molecule is this?

A

G-6P

Glucose-6-Phosphate

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27
Q

What Molecule is this?

A

G-1P

Glucose-1-Phosphate

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28
Q

What Enzyme is this?

A

Phosphoglucomutase

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29
Q

What Molecule is this?

A

G-6P

Glucose-6-Phosphate

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30
Q

What Molecule is this?

A

Glucose-1-Phosphate

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31
Q

What Molecule is this?

A

UTP

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32
Q

What Molecule is this?

A

UDP-Glucose

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33
Q

What Enzyme is this?

A

UDP-Glucose Phosphorylase

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34
Q

What Molecule is this?

A

UDP-Glucose

35
Q

What Molecule is this?

A

Glycogen

36
Q

What Molecule is this?

A

UDP

37
Q

What Molecule is this?

A

Glycogen (1 Unit More)

38
Q

What Enzyme is used in this reaction?

A

glycogen synthase

39
Q

What is the Glycogen Primer, the protien at the center of all glycogen that the branches grow off of?

A

Glycogenin protein

40
Q

An enzyme with _____activity adds UDP-glucose to a tyrosine

A

glucotransferase

41
Q

Initial catalysis of an octamer of glucose units is necessary to act as the substrate for____

A

glycogen synthase

42
Q

What is the function of branching, and what enzyme is responsible for it?

A

Branching serves to increase solubility and increases rate of synthesis and degradation by forming multiple termini.

Branching Enzyme

43
Q

What regulates Glycogen Synthesis, and how?

A

Glycogen synthase, interconversion of a and b forms through phosphorylation

44
Q

What stimulates the conversion of Glycogen Synthase between a and b forms?

A

PKA does phosphorylation of Glycogen Synthase Kinase (GSK3) and is controlled by glucagon and epinephrine (cell needs energy so turn off synthesis).

45
Q

What is the role of insulin in Glycogen Synthesis?

A

Insulin promotes glucose uptake and phosphorylation by the cell as well as inactivation of GSK3 to inhibit phosphorylation of glycogen synthase and activate glycogen synthesis.

46
Q

What is the PPP?

A

The Pentose Phosphate Pathway

47
Q

What are the three roles of the PPP?

A
  • Important source of NADPH (biosynthetic reducing power for fat synthesis)
  • Interconversion of 5 Carbon sugars from diet to useful 3C and 6C sugars that can be directed into glycolysis.
  • Synthesis of important pentose sugars needed for DNA and RNA synthesis.
48
Q

What is the overall reaction for PPP?

A

G-6-P + 2NADP+ ——-> Ribulose-5-P + 2NADPH + 2CO2

49
Q

What is Phase 1 of the PPP, and what happens?

A

Oxidative Phase

NADPH is formed through two sequential 2 e- oxidations

50
Q

What is Phase 2 of the PPP, and what happens?

A

Non-oxidative Phase

Interconversion of phophoryated sugars

51
Q

What happens in step 1 of the PPP, and what is the enzyme involved?

A

Oxidation of the C1 hemiacetal to a lactone (cyclic ester) the 2e- are transferred to NADP to make NADPH.

G-6-P dehydrogenase

52
Q

What happens in step 2 of the PPP, and what is the enzyme involved?

A

Hydration reaction and ring opens the lactone substrate to the carboxylic acid (a sugar acid).

lactonase

53
Q

What happens in step 3 of the PPP, and what is the enzyme involved?

A

Oxidative decarboxylation to generate the 5C product (a ketose) as well as another NADPH.

6-phosphogluconate dehydrogenase

54
Q

What step of the PPP is this, and what enzyme is used?

A

1

Glucose 6-Phosphate Dehydrogenase

55
Q

What step of the PPP is this, and what enzyme is used?

A

2

Lactonase

56
Q

What step of the PPP is this, and what enzyme is used?

A

3

6-Phosphogluconate Dehydrogenase

57
Q

What is this Molecule?

A

Glucose 6-Phosphate

58
Q

What is this Molecule?

A

6-Phosphoglucono-(sigma)-lactone

59
Q

What is this Molecule?

A

6-Phosphogluconate

60
Q

What is this Molecule?

A

Ribulose 5-Phosphate

61
Q

What is this Enzyme?

A

Glucose 6-Phosphate Dehydrogenase

62
Q

What is this Enzyme?

A

Lactonase

63
Q

What is this Enzyme?

A

6-Phosphogluconate Dehydrogenase

64
Q

What is this molecule?

A

Ribulose 5-Phosphate

ketose

65
Q

What is this Molecule?

A

Ribose 5-Phosphate

aldose

66
Q

What is this Enzyme?

A

Phosphopentose Isomerase

67
Q

Why is Ribose necessary in cells?

A
  • Ribose-5-P is a precursor to sugars needed to make RNA, DNA, ATP, NADH, FAD, coenzyme A etc.
  • Although Ribose-5-P is an important biosynthetic intermediate, the body has a greater need for NADPH.
  • Under these conditions (need for NADPH but not Ribose-5-P) the body can convert this 5C sugar into 3C and 6C sugars that feed into glycolysis.
68
Q

What are the three basic reactions in the conversion of 5C sugars?

A

C5 + C5 to C3 + C7

C3 + C7 to C6 + C4

C4 + C5 to C6 + C3

Total:3C5 to 2C6 + C3

69
Q

What is this Molecule?

A

Ribose 5-Phosphate

70
Q

What Molecule is this?

A

Ribulose 5-Phosphate

71
Q

What Molecule is this?

A

Xylulose 5-Phosphate

72
Q

What Enzyme is this?

A

Phosphopentose Isomerase

73
Q

What Enzyme is this?

A

Phosphopentose Epimerase

74
Q

What are these two Molecules?

A

Xylulose 5-P

Ribose 5-P

75
Q

What are these two Molecules?

A

G 3-P

Sedoheptulose 7-P

76
Q

What are these two Molecules?

A

Fructose 6-P

Erythrose 4-P

77
Q

What are these two Molecules?

A

Xylulose 5-P

Erythrose 4-P

78
Q

What are these two Molecules?

A

G 3-P

Fructose 6-P

79
Q

What is this Enzyme?

A

Transketolase

80
Q

What is this Enzyme?

A

Transaldolase

81
Q

What is this Enzyme?

A

Transketolase

82
Q

How is the PPP regulated?

A
  • The use of G-6-P is determined by 2 basic needs, energy (ATP) and biosynthetic reducing power (NADPH) for making fat.
  • Both of these molecules regulate glycolysis or PPP.
  • In the oxidative part of PPP, the first dehydrogenase is essentially irreversible, thus the logical regulatory point.
  • At low [NADP+] the three enzymes in the oxidative part of PPP have low activity (NADPH competes with binding to enzyme, is thus a competitive inhibitor).
83
Q

What three things does the fate of G-6-P depend on?

A

Need for NADPH

Need for ATP

Need Ribose-5-P

84
Q

Under different scenarios G-6-P is routed to which different pathways?

A

To Ribose-5-P

To recycling mode for NADPH formation

To pyruvate (ATP)

Biochemistry (12 decks)

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