18 - Glycogen Metabolism

• α-D-glucose

• α-1,4

• α-1,6

GLYCOGEN STRUCTURE

• a homopolymer of ____________

• linkage: _____

• branching: ______ (at about every 8-10 residues)

• osmotic stress

WHY STORE GLUCOSE AS GLYCOGEN?

• To minimize ______________

  • To store glucose at a concentration of that of typical glycogen stores, cells will be 0.4 M in glucose.

  • creates osmotic pressure; glucose leaks out of the cell

• Storing glucose as glycogen reduces osmotic pressure and is less energetically costly for the cell.

• blood glucose

• sudden

GLYCOGEN AS A FUEL RESERVE

• controlled breakdown of glycogen increases the amount of glucose that is available between meals

• glycogen is mobilized to maintain _______________ levels in between meals

• glucose from glycogen can provide energy whenever the requirement is _________ (as in during strenuous activity)

• 
  

  • distribution; organs

  • blood glucose

• energy production

MUSCLE AND LIVER GLYCOGEN

• liver glycogen is degraded for

  • ___________ to other __________ through the blood

  • maintaining proper __________ __________ levels

• muscle glycogen is degraded for its use in __________ ____________

• glycogen phosphorylase

ENZYMES INVOLVED

1. ___________________ – catalyzes phosphorolysis (bond cleavage by substitution of phosphate group) forming glucose 1-P

glycogen phosphorylase

ENZYMES INVOLVED

1. ______________

   • essential cofactor is pyridoxal phosphate

   • derived from Vitamin B6

• oligo glucantransferase

ENZYMES INVOLVED

2. debranching enzyme [aka _____ (α-1,6 to α-1,4) __________________]

• transferase

• α-1,6 glucosidase

ENZYMES INVOLVED

2. debranching enzyme [aka oligo (α-1,6 to α-1,4) glucantransferase]

   • transfers the terminal 3 glucose residues (__________________ activity)

   • cleaves an α-1,6 glycosidic bond (________________________ activity)

3. phosphoglucomutase

ENZYMES INVOLVED

3. __________________ - converts glucose 1-P to glucose 6-P

non-reducing

STEPS IN GLYCOGENOLYSIS -

• 
  

  

Glycogen phosphorylase can only attack and remove glucose units sequentially from the ____________ ends.

• phosphorylated

• glucose-1-P

  • glucose-6-P; phosphoglucomutase

STEPS IN GLYCOGENOLYSIS - Release of Glucose as Glucose 1-Phosphate

• glucose released is already ______________ without consuming ATP

• ___________ cannot leave the cell and go to the bloodstream

  • it readily enters the glycolytic pathway once it’s converted to _____________ by ____________________

• 4

STEPS IN GLYCOGENOLYSIS -

• action of glycogen phosphorylase continues until there are about _ residues left from the branch point

STEPS IN GLYCOGENOLYSIS - BIOENERGETICS OF THE PHOSPHOROLYSIS REACTION

• 
  

  

• Larger concentration of Pi than G1P

• What is tthe ration of G1P to Pi under normal cell conditions?

• Whaat makes the reaction thermodynamically favorable?

STEPS IN GLYCOGENOLYSIS -

• 
  

  

STEPS IN GLYCOGENOLYSIS -

• 
  

  

STEPS IN GLYCOGENOLYSIS -

• 
  

  

• dephosphorylated

  • blood glucose

  • brain; muscles

Fate of Glucose 1-Phosphate in the Liver

• glucose-1-P is ____________________

• free glucose exits the hepatic cells and goes into the blood stream for:

  • maintaining proper ______________ levels in between meals

  • transport to other organs (______ and ___________)

• glycolysis

• glucose-6-phosphatase

Fate of Glucose 1-Phosphate in the Muscle

• muscle cells degrade glycogen for its own need

• Glucose-1-P → Glucose 6-P → ____________

• Muscle cells lack __________________

1. UDP-glucose pyrophosphorylase

2. glycogen synthase

3. branching enzyme

GLYCOGENESIS - ENZYMES INVOLVED

1. ______________________ – creates UDPglucose, an activated glucose molecule

2. _________________ – primary enzyme responsible for growing the glycogen structure

3. _________________ – creates new non-reducing ends in the glycogen structure

• UDP-glucose; glycogen synthesis

• uridine triphosphate

GLYCOGENESIS - OVERVIEW

• _____________ is the activated form of glucose that serves as glucose donor for ________________

  • a sugar nucleotide
    
    

• UTP – ________________

GLYCOGENESIS -

• 
  

  

GLYCOGENESIS -

• 
  

  

GLYCOGENESIS -

• 
  

  

GLYCOGENESIS -

• 
  

  

GLYCOGENESIS -

• 
  

  

GLYCOGENESIS -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

• 
  

  

HORMONAL REGULATION OF GLYCOGEN METABOLISM -

•