Carbohydrate Metabolism
Glycogen Metabolism
Glycogenolysis à occurs in liver and muscles
• Glycogen à glucose when needed
Gluconeogensis Glycogenolysis
Glucose-6-phosphatase in ER of kidney and Liver + muscles
liver leads to location of reaction
Not allowed in skeletal muscle and brain
• Glycogen phosphorylase àprinciple enzyme of glycogen catabolism
o Glycogen -> G1P
o ∆G0 is + 3kJ/mol
o Reaction uses phosphate – reaction driven by high intracellular phosphate
levels: [Pi] ~ 100 x [glucose 1-P]
§ Dependent on ratio of G1P to inorganic phosphate
§ Allows for forward reaction to be favoured
o Shortening glycogen chain
à glycogen = polymer of glucose subunits linked by a(1à4) bonds
• Synthesized and stored when glucose levels are high
A+B →C+D
[𝑪][𝑫]
∆G = ∆Go + RT ln [𝑨][𝑩]
• Phosphoglucomutase à
o G1P -> G6P
o G6P used in glycolysis – no additional ATP needed (only the case when rxn
occurs in muscles)
§ Favorable to the cell!
§ Bypasses first step of glycolysis that does require ATP to add
phosphate to glucose
§ If glycogenolysis occurs in the liver à G6P or G1P must be converted
into glucose before being transported in bloodstream to muscle cells
§ ATP saving mechanism is only relevant in muscle cells
o Phosphate position is moved from carbon 1 to carbon 6
, o Reaction uses phosphate
§ Rxn is driven by high intracellular phosphate levels
*excess glucose is stored as glycogen in the liver
Glycogenesis à
• Glucose -> glycogen
• UDP- glucose pyrophosphorylase
o Glucose -> UDPG
o High concentration of phosphate in the liver favours glycogenolysis
o Glucose units are activated for transfer by formation of sugar nucleotides
§ Sugar nucleotides are used in synthesis of oligo and polysaccharides
o Addition of nucleotides activates molecules for subsequent reactions
o Mechanism =
§ Attack by a phosphate oxygen of G1P on the a-phosphorous of UTP
§ Loss of pyrophosphate anion
• 1 phosphate from G1P and 1 from UTP used
• Hydrolysis of pyrophosphate drives reaction forward
• UDP glucose is the glucose donor in glycogen synthesis
Glycogen Metabolism
Glycogenolysis à occurs in liver and muscles
• Glycogen à glucose when needed
Gluconeogensis Glycogenolysis
Glucose-6-phosphatase in ER of kidney and Liver + muscles
liver leads to location of reaction
Not allowed in skeletal muscle and brain
• Glycogen phosphorylase àprinciple enzyme of glycogen catabolism
o Glycogen -> G1P
o ∆G0 is + 3kJ/mol
o Reaction uses phosphate – reaction driven by high intracellular phosphate
levels: [Pi] ~ 100 x [glucose 1-P]
§ Dependent on ratio of G1P to inorganic phosphate
§ Allows for forward reaction to be favoured
o Shortening glycogen chain
à glycogen = polymer of glucose subunits linked by a(1à4) bonds
• Synthesized and stored when glucose levels are high
A+B →C+D
[𝑪][𝑫]
∆G = ∆Go + RT ln [𝑨][𝑩]
• Phosphoglucomutase à
o G1P -> G6P
o G6P used in glycolysis – no additional ATP needed (only the case when rxn
occurs in muscles)
§ Favorable to the cell!
§ Bypasses first step of glycolysis that does require ATP to add
phosphate to glucose
§ If glycogenolysis occurs in the liver à G6P or G1P must be converted
into glucose before being transported in bloodstream to muscle cells
§ ATP saving mechanism is only relevant in muscle cells
o Phosphate position is moved from carbon 1 to carbon 6
, o Reaction uses phosphate
§ Rxn is driven by high intracellular phosphate levels
*excess glucose is stored as glycogen in the liver
Glycogenesis à
• Glucose -> glycogen
• UDP- glucose pyrophosphorylase
o Glucose -> UDPG
o High concentration of phosphate in the liver favours glycogenolysis
o Glucose units are activated for transfer by formation of sugar nucleotides
§ Sugar nucleotides are used in synthesis of oligo and polysaccharides
o Addition of nucleotides activates molecules for subsequent reactions
o Mechanism =
§ Attack by a phosphate oxygen of G1P on the a-phosphorous of UTP
§ Loss of pyrophosphate anion
• 1 phosphate from G1P and 1 from UTP used
• Hydrolysis of pyrophosphate drives reaction forward
• UDP glucose is the glucose donor in glycogen synthesis
