Glycogen metabolism - glycogenesis

Question 1

____________________ catalyzes a phosphoryl shift between G6P and G1P.

Answer 1

Phosphoglucomutase

Question 2

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.

Answer 2

Anomeric carbon

Phosphate ester linkage

Question 3

What are four reasons why the structure of a sugar nucleotide is useful?

Answer 3

1. Formation is energetically favorable
2. Nucleotide can interact with the enzyme and contribute binding energy to facilitate catalysis
3. The nucleotidyl group is an excellent leaving group
4. Sugar nucleotides are set aside from other sugars

Question 4

What is the immediate precursor for glycogen synthesis?

Answer 4

Uridine diphosphate glucose

Question 5

What serves as the starting material for glycogen synthesis?

Answer 5

Sugar nucleotides

Question 6

Glucose-6-phosphate must be transformed into what compound before sugar nucleotide synthesis can occur?

Answer 6

Glucose-1-phosphate

Question 7

What enzyme catalyzes the formation of uridine diphosphate glucose?

Answer 7

Uridine diphosphate glucose pyrophosphorylase

Question 8

What is the mechanism of UDP-glucose pyrophosphorylase?

Answer 8

1. G1P attacks alpha P of UTP
2. Pyrophosphate leaves
3. Inorganic pyrophosphatase hydroyzes pyrophosphate into inorganic phosphate

Question 9

How is UDP glucose formed?

Answer 9

1.

Question 10

Why is the formation of UDP glucose irreversible?

Answer 10

Because pyrophosphate is removed by inorganic pyrophosphatase as soon as it was generated

Question 11

What are the two enzymes responsible for glycogenesis? Which of the two is the main enzyme?

Answer 11

Glycogen synthase

Glycogen branching enzyme

Glycogen synthase is the main enzyme

Question 12

What types of linkages can glycogen synthase form?

Answer 12

Alpha1–>4

Question 13

How many residues must be available on a non-reducing end for glycogen synthase to function?

Answer 13

Four

Question 14

Glycogen synthase catalyzes an irreversible or reversible reaction?

Answer 14

Irreversible

Question 15

Can glycogen synthase make branches?

Answer 15

No

Question 16

What is the mechanism of glycogen synthase?

Answer 16

1. O on glucose kicks back, expells UDP, and forms oxonium ion intermediate
2. Base deprotonates glycogen chain
3. O on glycogen attacks former anomeric C

Question 17

What enzyme catalyzes the formation of alpha1–>6 branches?

Answer 17

Glycogen branching enzyme

Question 18

How does glycogen branchin enzyme form alpha1–>6 linkages?

Answer 18

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

Question 19

A new branch point for glycogen must be a minimum of ____ units away from another branch point.

Answer 19

Four

Question 20

Can glycogen synthase initiate a new glycogen chain?

Answer 20

No, it can only add glucose units to an existing chain of at least 8 glucose units

Question 21

How does glycogen synthesis begin?

Answer 21

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

Question 22

What is the role of glycogenin?

Answer 22

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

Question 23

To what amino acid residue does glycogenin add glucose?

Answer 23

Tyrosine

Question 24

More branching of glycogen results in more reducing ends and ___________________ solubility.

Answer 24

Increased