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Biochemistry I > Chapter 15: Glycogen Synthesis and Degradation > Flashcards

Chapter 15: Glycogen Synthesis and Degradation Flashcards

1
Q

Glycogen molecule

A
  • Highly branched with non-reducing ends
  • Glucose residues linked by alpha-1,4-glycosidic bonds
  • Alpha-1,6-glycosidic bonds every 10 residues
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2
Q

Glycogen

A
  • The storage form of glucose
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3
Q

Glycogen synthesis involves

A
  • Phosphoglucomutase
  • Formation of UDP-glucose
  • Addition of UDP-glucose to glycogen polymer
  • Formation of branches
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4
Q

Glycogen degradation involves

A
  • Phosphorolytic cleavage
  • Debranching enzyme
  • Phosphoglucomutase
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5
Q

Alpha-1,4-glycosidic linkages

A
  • Linear linkages of glycogen molecules
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6
Q

Alpha-1,6-glycosidic linkages

A
  • Branching linkages of glycogen molecules
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7
Q

Liver glycogen

A
  • Used for export to maintain blood sugar levels and for use by other tissues
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8
Q

Glycogen synthesis (glycogenesis)

A
  • Ongoing in all tissues
  • Phosphoglucomutase
  • Formation of active glucose
  • Transfer of UDP-glucose to glycogen
  • Formation of branches
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9
Q

Phosphoglucomutase reaction

A
  • Synthesis of glucose-1-phosphate from glucose-6-phosphate (hexokinase)
  • Near equilibrium
  • Intramolecular transfer of phosphate
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10
Q

Formation of active glucose (UDPG)

A
  • UDP-glucose phosphorylase

- Accomplished by combining a uridyl phosphate residue with the phosphate group on the #1 carbon of G1P

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11
Q

Glycogen synthase catalyzes

A
  • Breaking of ester bond between C1 of glucose and the pyrophosphate of UDP
  • Formation of a new alpha-1,4-glycosidic bond (between C1 of glucose residue and C4 hydroxyl on a terminal glucose residue)
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12
Q

The reducing end of the glucose molecule (C1)

A
  • Is always added to the non-reducing end of the growing glycogen molecule that is longer than 4 residues
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13
Q

Length of the polymer increases

A
  • One by one
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14
Q

Glycogen synthase cannot make

A
  • Alpha-1,6-glycosidic linkages
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15
Q

UDP-glucose is added to the glycogen chain via

A
  • An alpha-1,4-glycosidic bond extending the glycogen polymer by 1 glucose unit
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16
Q

1,4-alpha glucan

A
  • Branching enzyme that forms branches on glycogen molecule

- Increases glycogen solubility

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17
Q

Block of 7 glucose residues

A
  • Moves from the end of a chain onto the C6 hydroxyl of a neighboring chain
  • Forms an alpha-1,6-glycosidic bond
  • Occurs at a point from at least 4 residues removed form nearest branch
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18
Q

Andersen’s Disease

A
  • Branching enzyme is defective
  • Formation of long unbranched glycogen
  • Glycogen precipitates in heart and liver
  • Cirrhosis and death
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19
Q

Anderson’s disease creates linear polymers

A
  • Decreases glycogen solubility
20
Q

Primer

A
  • Required for glycogen synthesis
21
Q

Glycogen synthase primer

A
  • Tyrosine residue on the glycogenin enzyme
22
Q

Glycogenin

A
  • Glycotransferase

- Has tyrosine residue that contains the glycogen synthase primer

23
Q

UDP-glucose

A
  • Added to the glycosylated glycogen until it reaches optimal density
24
Q

Glycogen exerts a negative feedback effect on glycogen synthase

A
  • Promotes the a –> b transition
25
Q

Glycogenin is self-glycosylating

A
  • Capable of adding glucose/sugars to itself (scaffold and an enzyme)
26
Q

Glycogen phosphorylase

A
  • Phosphorolytic cleavage
27
Q

Debranching enzymes

A
  • 4-alpha-D-glucotransferase

- Amylo-alpha-1,6-glucosidase

28
Q

Glycogen degradation (glycogenolysis) involves

A
  • Glycogen phosphorylase
  • Debranching enzymes
  • Phosphoglucomutase
29
Q

2 activities of the glycogen degradation bifunctional enzyme

A
  • Move glucose units

- Hydrolytic activity where cleavage of 1,6 occurs

30
Q

Anaerboic glycolysis products

A
  • Investment of 2 ATP
  • Extraction of 4 ATP
  • 2 net ATP overall
31
Q

Phosphorylated glucose from glycogen is glucose-1-phosphate

A
  • Can enter glycolysis
  • Bypass the hexokinase step
  • Produces 3 ATP as opposed to 2 ATP from normal anaerobic glycolysis (where glucose enters unphosphorylated)
32
Q

Glycogen phosphorylase

A
  • Phosphorolysis of the alpha-1,4-glycosidic bonds (yields G1P)
  • Requires pyridoxal phosphate prosthetic group
  • Cleaves the 1,4 bonds up to four residues from a branch point
33
Q

Phosphorolytic cleavage occurs at

A
  • The non-reducing terminal of the glycogen molecule
34
Q

Phosphorolytic cleavage is reversible, but

A
  • Favors formation of G1P
  • Produces 3 molecules of ATP
  • Anaerobic glycolysis (hexokinase not required)
35
Q

Complete aerobic oxidation produces

A
  • 33 molecules of ATP
36
Q

Proteolytic cleavage does not require

A
  • Utilization of ATP to produce a phosphorylated product
37
Q

G1P can enter the glycolysis

A
  • Glucose comes in phosphorylated
  • Coverted to G6P
  • Glycolysis continues
38
Q

4-alpha-D-glucotransferase

A
  • Transfers the glycogen molecules during debranching
39
Q

Amylo-alpha-1,6-glucosidase

A
  • Final debranching enzyme

- Hydrolytic cleavage

40
Q

There is a limit to which the phosphorylase enzyme debranches

A
  • It will move 3 glucose units to the core leaving one behind
41
Q

Transferase followed by hydrolytic cleavage

A
  • Produces free glucose
42
Q

Phosphoglucomutase

A
  • Catalyzes the conversion of G1P to G6P
  • Near equilibrium
  • Used in both synthesis and degradation of glycogen
43
Q

Phosphorylated compounds

A
  • Do not readily diffuse out of cells
44
Q

G6P in the liver

A
  • Can be converted to glucose and Pi-G6Pase
45
Q

G6P formed in the muscle

A
  • From glycogen breakdown
  • Can only be used in the muscle
  • Muscle lacks G6Pase

Biochemistry I (34 decks)

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