Glycogen

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Glycogen

• The really sweet stuff.

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A Word on Sugar

• Stored in both plants and animals
• Plants Many forms
• Animals Glycogen
• Why are sugars important?
• Primary source of energy for many tissues.

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Sugar Vocabulary

• Saccharide The chemical name for a sugar.
• Mono one sugar
• Di two sugars
• Poly many sugars
• Glycosidic Linkage The chemical bond that
  connects sugar molecules, forming a disaccharide
  or polysaccharide.
• ? 1?4
• ? 1?6
• ß 1?4

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Sugar Vocabulary

• Reducing end The end of a polysaccharide where
  no sugars are added or removed.
• Non-reducing end The end of a polysaccharide
  where sugars are added or removed.

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What is Starch?

• Starch is a molecule that is made of many
  individual sugar molecules.
• Eg.
• Amylose
• Cellulose
• Amylopectin
• Glycogen

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Make Like a Tree

• Many starches have a branching pattern.
• Glycogen Every 10 Glucose
• Amylopectin Every 30 Glucose
• This has several benefits.
• Increased water solubility.
• Many non-reducing ends.
• Increased rate of formation and degradation.

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Just the Facts

• Location
• Stored in the cytosol.
• Muscle 400g
• Liver 100g
• Goal
• Store Glucose for
• later use.

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Just the Facts

• Common bonds
• ? 1?4 (chain)
• ? 1?6 (branch)
• Branches
• About every 10 glucoses

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A Fork in the Road

• Glycogen Metabolism has two paths to consider.
• Synthesis Formation of glycogen.
• Degradation Breakdown of glycogen.

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Build It And They Will Come

• Glycogen Synthesis
• Three Parts
• Initiation
• Elongation
• Branching

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Initiation

• Changing G-6-P to G-1-P.
• Formation of UDP Glucose.
• UDP Glucose is then attached to Glycogenin by the
  enzyme
• Glycogen Initiator Synthase

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Glycogenin

• Glycogenin acts as an anchor to build the
  glycogen molecule on.

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Stretch It Out

• Elongation The addition of glucose to the
  glycogen molecule through the formation of ? 1?4
  glycosidic bonds.
• This is accomplished by the enzyme
• Glycogen Synthase

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Branch Out

• Branching The formation of a side chain of
  glucose, using an ? 1?6 glycosidic bond.
• This is accomplished using the enzyme
• Glucosyl 46 Transferase

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Breakdown

• Glycogen Degradation
• Enzymes involved
• Glycogen Phosphorylase
• Glucosyl 44 Transferase
• Amylo-?-(1,6)-Glucosidase

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Like Taking Candy

• Glycogen Phosphorylase
• Cleaves the ? 1?4 bond by phosphorylatiing the
  glucose on the non-reducing end of glycogen.

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Road Block

• Glycogen Phosphorylase can only remove glucoses
  that are more than four molecules away from the
  branch point.
• To overcome this obstacle another enzyme is
  utilized.

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Trimming the Tree

• Degrading the branches of Glycogen.
• Two enzymes required
• Glucosyl 44 Transferase
• Cuts off the outer three glucose.
• Amylo-?-(1,6)-Glucosidase
• Cuts off the last glucose of the branch.

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Do It All Again

• Once the branch is removed Glycogen Phosphorylase
  takes over again, and the process continues.

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Regulation

• Glycogen Synthesis
• Stimulation
• Glucose
• ATP
• Insulin

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Regulation

• Glycogen Synthesis
• Inhibition
• Low Glucose
• ADP
• Glucagon

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Regulation

• Glycogen Degradation
• Stimulation
• Low Glucose
• ADP
• Glucagon
• Calcium

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Regulation

• Glycogen Degradation
• Inhibition
• Glucose
• ATP
• Insulin