Chapter 25: Glycogen Synthesis

Question 1

Glycogen degradation yields…

Answer 1

Glucose 1-Phosphate

Question 2

Glycogen synthesis requires…

Answer 2

UDP-Glucose

Question 3

What is UDP-Glucose?

Give:

• full name
• purpose
• how it is synthesized
• how it is rendered irreversible

Answer 3

• Uridine diphosphate-glucose (activated form of glucose)
• Is the glucose donor in glycogen synthesis.
• Synthesized by UDP-Glucose pyrophosphorylase
• The reaction is rendered irreversible by the hydrolysis of pyrophosphate

Question 4

What catalyzes the transfer of glucose from UDP-Glucose to a growing chain?

Answer 4

Glycogen Synthase

Question 5

Activated glucosyl unit of UDP-glucose is attached to glycogen by _____ catalyzed by _____.

Answer 5

Attached by a-1,4 glycosidic bond

Catalyzed by glycogen synthase

Question 6

Glycogen synthesis requires an oligosaccharide of glucose residues as _____.

Answer 6

Primer (Need a chain of 7 or 8)

Question 7

What synthesizes glycogen synthase’s primer?

Answer 7

Glycogenin - generates an oligosaccharide of glucose residues 8 molecules long. Considered a glucosyl transferase

Question 8

Glycogen synthase can only synthesize _____.

Answer 8

a-1,4 linkages

Question 9

A branching enzyme forms _____. What does this do?

Answer 9

a-1,6 linkages

Branching of glycogen increases its solubility and the rate of its synthesis and degradation.

Question 10

Glycogen synthesis is regulated by?

Answer 10

Reversible phosphorylation

Question 11

What is the key regulatory enzyme in glycogen synthesis?

Answer 11

Glycogen synthase

*Similar to glycogen phosphorylase but has the opposite effect

Question 12

Glycogen synthase is _____ when in phosphorylated b form?

Answer 12

Inactive

Question 13

Glycogen synthase is _____ when in unphosphorylated a form?

Answer 13

Active

Question 14

Glycogen is an effective _____ of glucose.

Answer 14

Storage form

Question 15

Only _____ is required to incorporate glucose 6-phosphate into glycogen.

Answer 15

One molecule of ATP

Question 16

The complete oxidation of glucose derived from glycogen yields _____.

Answer 16

31 molecules of ATP

Question 17

The overall efficiency of storage is nearly _____.

Answer 17

97%

Question 18

Glycogen synthesis is inhibited by the same _____ and _____ that stimulate glycogen breakdown.

Answer 18

Glucagon and epinephrine signaling pathways

Question 19

What stimulates glycogen breakdown and how?

Answer 19

Protein Kinase A (PKA) stimulates by phosphorylating and activating phosphorylase kinase

Question 20

How does PKA inhibit glycogen synthesis?

Answer 20

Inhibits by inactivating glycogen synthase by phosphorylation

Question 21

Glycogen synthase kinase also…

Answer 21

Phosphorylates and inhibits glycogen synthase

Question 22

Glycogen Degradation is _____ by phosphorylation.

Answer 22

Activated

Question 23

Glycogen Synthesis is _____ by phosphorylation.

Answer 23

Inhibited

Question 24

What reverses the regulatory effects of kinases on glycogen metabolism?

Answer 24

Protein Phosphatase 1 (PP1)

Question 25

PP1 _____ glycogen synthesis.

Answer 25

PP1 activates

Question 26

PP1 _____ glycogen degradation.

Answer 26

PP1 inhibits

Question 27

Insulin _____ glycogen synthesis. How?

Answer 27

Stimulates by _inactivating glycogen synthase kinase_ (it's kept unphosphorylated)

Question 28

In summary, glucagon and epinephrine regulate glycogen metabolism by:

Answer 28

G&E: Stimulating glycogen degradation G&E: Inhibiting glycogen synthesis

Question 29

In summary, insulin regulates glycogen metabolism by:

Answer 29

I: Stimulating glycogen synthesis I: Inhibiting glycogen degradation

Question 30

Low blood glucose levels means \_\_\_\_\_. This requires...

Answer 30

Hypoglycemia Glucagon (starved or fasting state)

Question 31

High blood glucose levels means \_\_\_\_\_. This requires...

Answer 31

Hyperglycemia Insulin (fed state)

Question 32

Diabetes is characterized by...

Answer 32

The presence of **excess glucose** and underutilization of glucose. This excess glucose is excreted in the urine.

Question 33

What happens with type 1 diabetes?

Answer 33

Insulin is *not* produced (10% of diabetic patients)

Question 34

What happens will type 2 diabetes?

Answer 34

Insulin *is* produced, but the **insulin-signaling pathway is not responsive** (insulin resistance)

Question 35

During diabetes, _____ is produced in excess.

Answer 35

Glucagon

Question 36

What is von Gierke disease (type I)?

Answer 36

* Massive _enlargement of the liver_ and _hypoglycemia_ due to the **lack of glucose 6-phosphatase** from the liver. * Mutations in the gene encoding of the glucose 6-phosphate transporter also cause von Gierke disease * Cannot get into the ER lumen to produce glucose

Question 37

What is Cori disease (type III)?

Answer 37

_Structure of liver_ and _muscle glycogen abnormal_ and _glycogen amount increased_ due to **lack of debraching enzyme**

Question 38

What is McArdle disease (type V)?

Answer 38

* Results from **defective muscle glycogen phosphorylase** (Not able to degrade glycogen - _losing ATP source_) * Painful cramps occur when patients with McArdle disease exercise * Even when walking, they have muscle cramps due to lack of ATP

Question 39

A deficiency in the glycogen phosphorylase in liver would result in: * hemolytic anemia. * hyperglycemia. * hypoglycemia. * lactic acidosis. * muscle cramps.

Answer 39

Hypoglycemia

Question 40

The glycogen phosphorylase *b* in muscle is allosterically inhibited by high levels of: * AMP * NADH * fructose 2,6-bisphosphate * UDP-glucose * glucose 6-phosphate

Answer 40

Glucose 6-Phosphate

Question 41

T or F: Active protein phosphatase 1 (PP1) inhibits glycogen synthesis and stimulates glycogen degradation.

Answer 41

FALSE

Question 42

T or F: Glycogen synthesis requires UDP-glucose, an activated form of glucose.

Answer 42

TRUE

Question 43

T or F: Insulin stimulates glycogen synthesis by preventing the phosphorylation of glycogen synthase.

Answer 43

True

Question 44

T or F: Glycogen synthase requires an oligosaccharide of glucose residues as a primer, which is synthesized by the enzyme glycogenin.

Answer 44

True

Question 45

Diabetes mellitus results from _______________ insufficiency and _______________ excess. * epinephrine; insulin * glucagon; epinephrine * glucagon; insulin * leptin; epinephrine * insulin; glucagon

Answer 45

Insulin; glucagon