03: Carbohydrate Metabolism: Glycogenesis and Glycogenolysis Notes

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glycogen link as

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α-(1,4) glycosidic linkage

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There is only one reducing end of glycogen;

it is “capped” by a protein called _____

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glycogenin

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37 Terms

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glycogen link as

α-(1,4) glycosidic linkage

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There is only one reducing end of glycogen;

it is “capped” by a protein called _____

glycogenin

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Glycogen is a ____ process

anabolic

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glycogenin is connected to amino acid

Tyrosine (Tyr,Y)

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Glycogenesis Step 1

Conversion of glucose 6-phosphate to glucose 1-phosphate, Phosphoglucomutase

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Glycogenesis Step 2

Synthesis of UDP-glucose, UDP-glucose pyrophosphorylase

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Glycogenesis Step 3

Synthesis of an initiating primer, Glycogenin

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Glycogenesis Step 4

Chain elongation, Glycogen synthase

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Glycogenesis Step 5

Formation of branches, (creation of 1,6 branches and extension of 1,4 branched chain), 4:6 transferase (branching enzyme)

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The breakdown of glycogen to release glucose 1-phosphate and α-D-glucose

Glycogenolysis

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Glycogenolysis is a _____ pathway

catabolic

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Glycogenolysis Step 1

Shortening of glycosidic chains, Glycogen phosphorylase

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Glycogenolysis Step 2

De-branching (move 3 residues), 4:4 transferase (debranching enzyme #1)

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Glycogenolysis Step 3

De-branching (remove 1 glucose), 1:6 glucosidase (debranching enzyme #2)

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Glycogenolysis Step 4

Conversion of glucose 1-phosphate to glucose 6-phosphate, Phosphoglucomutase

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Step 1: Shortening of glycosidic chains

  • Enzyme continues until four glucosyl units remain from the branch point

    • This four unit “stump” is called _______

limit dextrin

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Step 2: Debranching (remove 3 units)

  • _____ initiates the action of a debranching enzyme

Limit dextrin

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Glycogenolysis: Step 3: Debranching (remove 1 glucose) 

  • ________ is used again for degradation if needed

Glycogen phosphorylase

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Glycogenolysis: Conversion of glucose 1-phosphate to glucose 6-phosphate

  • Glucose 6-phosphate is transported to the ER by glucose 6-phosphate _____

translocase

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Glycogenolysis: Conversion of glucose 1-phosphate to glucose 6-phosphate

  • In the ER, glucose 6-phosphate is converted to glucose by glucose 6 - _____

phosphatase

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Muscle lacks _______

glucose 6-phosphatase

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Glycogen breakdown:

________ works on non-reducing ends until it reaches four residues from an (16) branch point.

Glycogen phosphorylase

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Glycogen breakdown: ______ transfers a block of three residues to the non-reducing end of the chain

Debranching enzyme #1

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Glycogen breakdown: _______ cleaves the single remaining (16)-linked glucose, which becomes a free glucose unit (i.e., NOT glucose-1-phosphate).

Debranching enzyme #2

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In the liver

  • Well fed state: ______ accelerates

glycogenesis

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In the liver

  • Fasting state: ______ accelerates

glycogenolysis

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In the muscle

  • Active exercise: _______ accelerates

glycogenolysis

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In the muscle

  • At rest: _____ accelerates

glycogenesis

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_____ and ______ are hormonally regulated by insulin, glucagon and epinephrine (aka adrenaline)

Glycogen phosphorylase and glycogen synthase

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Glycogen phosphorylase and glycogen synthase are hormonally regulated by_______ (aka adrenaline)

insulin, glucagon and epinephrine

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____ generally opposes the effects of glucagon and epinephrine

Insulin

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____ favors glycogen synthesis

Insulin

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Glucagon and epinephrine favor glycogen _____

breakdown

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Insulin binds to a receptor and activates a _____

tyrosine kinase

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Activated Protein Phosphatase-1 (PP-1) activates ______

  • Leads to glycogen synthesis

glycogen synthase

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Activated Protein Phosphatase-1 (PP-1) inhibits ______

  • Phosphorylase kinase activates glycogen phosphorylase

  • Inhibition of phosphorylase kinase thus prevents the breakdown of glycogen

  • Indirect inhibition of glycogen phosphorylase

phosphorylase kinase

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Epinephrine or glucagon activates ____

  • catalyzes the generation of cyclic AMP (cAMP)

  • cAMP activates a cAMP-dependent protein kinase

    • Higher the levels of cAMP, greater the number of activated protein kinase molecules\

  • cAMP-dependent protein kinase phosphorylates both glycogen synthase and glycogen phosphorylase

    • Glycogen synthase becomes inactive; glycogen synthesis stops

    • Glycogen phosphorylase becomes active; glycogen breakdown is favored

adenylyl cyclase