Glycogen Metabolism Flashcards
(32 cards)
in what form is glucose stored in human body
glycogen
Where in the body does glycogen synthesis and breakdown occur?
liver and skeletal muscle
What types of linkages btw glucose molecules may be found in glycogen?
alpha-1,4-glycosidic bonds (straight chain linkage)
alpha-1,6-glycosidc bonds (branch points)
Where in the cell does glycogen synthesis occur?
Cytosol
What molecules provide the energy for glycogen synthesis
ATP
UTP
1st step in synthesis of glycogen from glucose?
glucose 6P –> glucose 1P
enzyme that catalyzes 1st rxn?
phosphoglucomutase
UDP glucose pyprophosphorylase catalyzes
Glucose + UDP –> UDP-glucose
What protein serves as primer for glycogen synthesis?
glycogenin
What reaction does glycogen initiator synthase catalyze?
UDP-glucose + glycogenin + glucose –> UDP + linked glucose molecules
enzyme responsible for creating the alpha-1,4 linkage btw glucose molecules?
Glycogen Synthase
can glycogen synthase initiate glycogen synthesis de novo?
no, it can only elongate an existing glycogen chain
where on the newly synthesized glycogen chain are new glucose molecules added?
to the non reducing end
What would be the shape of a glycogen molecule if glycogen synthase was the only enzyme adding glucose to the the chain?
Linear
What is the enzyme responsible for creating alpha 1,6 glycosidic bonds between glucose molecules?
1,4-alpha-glucan branching enzyme
How does branching enzyme work?
transfers approximately 5-8 glucose residues from non reducing end of glycogen chain to another residue with the chain and attaches the residues via an alpha 1,6 linkage
What is the purpose of branching glycogen molecules?
to facilitate buildup of glycogen
increases solubility of glycogen
creates a large number of terminal residues, which are substrates for Glycogen Synthase and Glycogen Phosphorylase
When is glycogen used as fuel
during strenuous exercise in muscle, fasted state in liver
is the process of glycogen breakdown the reverse of glycogen synthesis?
no
What enzyme is used to break down glycogen
Glycogen Phosphorylase
Where does the glycogen phosphorylase cleave the glycogen molecule?
at the alpha 1,4 glycosidic bond
How far away from the reducing end of the glycogen molecule can glycogen phosphorylase cleave?
discontinues cleavage when there are 4 glucose residues remaining on chain
What enzyme removes glycogen branches?
debranching enzyme
What are the 2 components of debranching enzyme complex?
Transferase which removes the 1st there glucose residues left on a branch of glycogen.
alpha 1,6-glucosidase- removes the last glucose residue on a branch of glycogen
