Glycogen metabolism - glycogenesis Flashcards
____________________ catalyzes a phosphoryl shift between G6P and G1P.
Phosphoglucomutase
Sugar nucleotides play an important role in many biochemical reactions; they involve a linkage between the ______________ carbon on a sugar and a nucleotide via a ________________ ________________ linkage.
Anomeric carbon
Phosphate ester linkage
What are four reasons why the structure of a sugar nucleotide is useful?
- Formation is energetically favorable
- Nucleotide can interact with the enzyme and contribute binding energy to facilitate catalysis
- The nucleotidyl group is an excellent leaving group
- Sugar nucleotides are set aside from other sugars
What is the immediate precursor for glycogen synthesis?
Uridine diphosphate glucose
What serves as the starting material for glycogen synthesis?
Sugar nucleotides
Glucose-6-phosphate must be transformed into what compound before sugar nucleotide synthesis can occur?
Glucose-1-phosphate
What enzyme catalyzes the formation of uridine diphosphate glucose?
Uridine diphosphate glucose pyrophosphorylase
What is the mechanism of UDP-glucose pyrophosphorylase?
- G1P attacks alpha P of UTP
- Pyrophosphate leaves
- Inorganic pyrophosphatase hydroyzes pyrophosphate into inorganic phosphate
How is UDP glucose formed?
1.
Why is the formation of UDP glucose irreversible?
Because pyrophosphate is removed by inorganic pyrophosphatase as soon as it was generated
What are the two enzymes responsible for glycogenesis? Which of the two is the main enzyme?
Glycogen synthase
Glycogen branching enzyme
Glycogen synthase is the main enzyme
What types of linkages can glycogen synthase form?
Alpha1–>4
How many residues must be available on a non-reducing end for glycogen synthase to function?
Four
Glycogen synthase catalyzes an irreversible or reversible reaction?
Irreversible
Can glycogen synthase make branches?
No
What is the mechanism of glycogen synthase?
- O on glucose kicks back, expells UDP, and forms oxonium ion intermediate
- Base deprotonates glycogen chain
- O on glycogen attacks former anomeric C
What enzyme catalyzes the formation of alpha1–>6 branches?
Glycogen branching enzyme
How does glycogen branchin enzyme form alpha1–>6 linkages?
By transfer of the last 6 to 8 residues from the non-reducing end of a chain with at least 11 residues to a C06 hydroxyl on an interior position
A new branch point for glycogen must be a minimum of ____ units away from another branch point.
Four
Can glycogen synthase initiate a new glycogen chain?
No, it can only add glucose units to an existing chain of at least 8 glucose units
How does glycogen synthesis begin?
Glycogenein is a protein/enzyme found at the core of all glycogen particles; it covalently attaches glucose to a tyrosine residue and adds glucose units to extend the primer to about 8 glucose residues
What is the role of glycogenin?
It is a protein/enzyme that covalently attaches glucose to tyrosine residues and continues to do so until enough glucose residues are linked together for glycogen synthase to take over
To what amino acid residue does glycogenin add glucose?
Tyrosine
More branching of glycogen results in more reducing ends and ___________________ solubility.
Increased
