BIOC2101 Lecture 10: Glycogen
Glycogen
• Storage polysaccharides
o Glycogen - animals, fungi, bacteria
o Starch - plants
▪ Living organisms can use glycogen or starch to store glucose for later metabolic use
o
o Glycogen
▪ What and where
• Storage polysaccharide of animals
• Present in all cells
• Most prevalent in skeletal muscle and liver - Occurs in cytoplasmic granules
• Muscle cells
• Contain up to 1-2% glycogen by weight
• Liver cells
• Contain up to 10% glycogen by weight
• Glycogen granules contain
• Enzymes that catalyse glycogen synthesis and breakdown
• Many proteins that regulate these processes
▪ Function
• Constant supply of glucose is essential for tissues (brain and red blood cells)
• Liver
• Mobilisation of glucose from glycogen stores
• Provides a constant supply of glucose to ALL tissues
• Muscle
• Low levels of glycogens degraded
• Phosphorolytic cleavage and glycolysis
• Provide ATP for local muscle contraction
• Glycogen synthesis accelerates when there is an abundance of glucose
• E.g. After a meal
▪ Structural features
• Main backbone
• Glucose units
•
glycosidic bonds
• Branches
• Glucose units connected to backbone
• glycosidic bonds
• Occurs once every tenth glucose (in main chain)
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•
• Highly branched
• Glycogen molecule can be expanded quickly
• Quick synthesis and breakdown
• Glucose residues added to many ends
• Glucose broken off branches simultaneously
•
• Single reducing end - Glucose with a free hydroxyl group on C1
• Many 'non-reducing' ends - Glucose with a free hydroxyl group on C4
•
• Helical
• Main backbone folds into a helical arrangement ( glycosidic
bonds)
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•
•
• The structure of glycogen - a branched polymer of glucose
• Add glucose to non-reducing ends
• Many non-reducing ends
• Single reducing end
Glucose metabolism
•
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