Glycogen metabolism in muscle and liver Flashcards
What are the linkages in glycogen
alpha-1,4 and alpha-1,6.
Outline the steps of glycogen breakdown in the muscle
Glycogen—->G1P–r–>G6P which can enters glycolysis and becomes pyruvate. G1P—>G6P is reversible and catalysed by phosphoglucomutase.
Outline the steps of glycogen breakdown in the liver
Glycogen—–>G1P–r–>G6P——>glucose
What enzyme catalysis G6P to glucose in the liver
glucose-6-phosphatase
What enzyme breaks the alpha 1-4 linkages in glycogen
Glycogen phosphorylase to form G1P And a the glycogen molecule.
It can only break bonds up to 4 glucose residues from a branching point.
outline the debranching of glycogen
Transferase activity removes 3 residues from the branch and transfers them to the end of another chain in an alpha 1,4 linkage. The free glucose left at the end of the chain is removed via alpha 1,6-glucosidase
the chain can be broken down by phosphorylase until it meets the next branch point.
Glycogen synthesis
Glucose——->G6P
G6P—R—>G1P (phosphoglucomutase)
G1P + UTP—–>UDP-glucose
UDP-glucose +glycogen—–> Glycogen(n+1) +UDP (glycogen synthase)
describe the action of branching enzyme
transfers a block of 7 residues from a growing chain to create a new branch with an alpha-1,6 linkage
Why is glycogen a good energy store
It can be mobilised very rapidly
enzymes phosphorylase and glycogen synthase are very sensitive to regulation by hormones, stress and muscle contraction
the branched structure provides a large number of ends which the polymer can be added to or broken down
Allosteric regulation of phosphorylase
subject to allosteric regulation by AMP, ATP and G6P
When AMP is hight ATP is low so phosphorylase is activated.
ATP and G6P compete with AMP binding which inhibits phosphorylase.
Allosteric regulation of Glycogen synthase
Glycogen synthase is allosterically activated by G6P, glycogen synthesis is activated when G6P is plentiful.
