03: Carbohydrate Metabolism: Glycogenesis and Glycogenolysis Notes

glycogen link as

α-(1,4) glycosidic linkage

There is only one reducing end of glycogen;

it is “capped” by a protein called _____

glycogenin

Glycogen is a ____ process

anabolic

glycogenin is connected to amino acid

Tyrosine (Tyr,Y)

Glycogenesis Step 1

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

Glycogenesis Step 2

Synthesis of UDP-glucose, UDP-glucose pyrophosphorylase

Glycogenesis Step 3

Synthesis of an initiating primer, Glycogenin

Glycogenesis Step 4

Chain elongation, Glycogen synthase

Glycogenesis Step 5

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

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

Glycogenolysis

Glycogenolysis is a _____ pathway

catabolic

Glycogenolysis Step 1

Shortening of glycosidic chains, Glycogen phosphorylase

Glycogenolysis Step 2

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

Glycogenolysis Step 3

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

Glycogenolysis Step 4

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

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

Step 2: Debranching (remove 3 units)

• _____ initiates the action of a debranching enzyme

Limit dextrin

Glycogenolysis: Step 3: Debranching (remove 1 glucose) 

• ________ is used again for degradation if needed

Glycogen phosphorylase

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

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

translocase

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

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

phosphatase

Muscle lacks _______

glucose 6-phosphatase

Glycogen breakdown:

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

Glycogen phosphorylase

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

Debranching enzyme #1

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

In the liver

• Well fed state: ______ accelerates

glycogenesis

In the liver

• Fasting state: ______ accelerates

glycogenolysis

In the muscle

• Active exercise: _______ accelerates

glycogenolysis

In the muscle

• At rest: _____ accelerates

glycogenesis

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

Glycogen phosphorylase and glycogen synthase

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

insulin, glucagon and epinephrine

____ generally opposes the effects of glucagon and epinephrine

Insulin

____ favors glycogen synthesis

Insulin

Glucagon and epinephrine favor glycogen _____

breakdown

Insulin binds to a receptor and activates a _____

tyrosine kinase

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

• Leads to glycogen synthesis

glycogen synthase

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

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