Glycogen Synthesis And Degradation

Front 1

Where is glycogen found?

Back 1

In all cell types in tissues that respond to fuel hormones

Front 2

What two factors increase glycogen degradation?

Back 2

a) low fuel supplies b) response to stress or other metabolic need

Front 3

What factor increases glycogen synthesis?

Back 3

excess carbohydrates

Front 4

In glycogen, what type of linkage do you find in a) branching points… b) linear polymer?

Back 4

a) ∂-1,6 linkage… b) ∂-1,4 linkage

Front 5

What is the starting point for glycogen synthesis?

Back 5

Glycogenin protein acts like a primer (autoglycosylation)

Front 6

What happens after glycogenin adds 5-7 glucose molecules to the growing poylmer?

Back 6

glycogen synthase starts elongating the polymer

Front 7

Where are UDP-glucose molecules added?

Back 7

At the reducing end

Front 8

What is the value in having glycogen branch?

Back 8

Degradation occurs through exoglycosylase, which means it starts at the ends (more branches = more ends = faster degradation)… also more reducing ends = faster synthesis

Front 9

Which enzyme makes glucose synthesis possible (export)? And where is it found?

Back 9

a)glucose-6-phosphatase (G6Pase), b) only in the liver

Front 10

Which organ can dephosphorylate and export glucose?

Back 10

Only the liver

Front 11

What can organs, other than the liver, do with glucose?

Back 11

Use it

Front 12

What is the chain of events after low blood sugar occurs?

Back 12

decreased glucagon ratio > glycogenolysis > inhibitioin of glycogen synthesis

Front 13

What effect does epinephrine have on glycogen?

Back 13

epi activates glygenolysis to mobilize stored energy

Front 14

Can muscles make glycogen?

Back 14

Yes, they have GLUT4, insulin receptors… thus they use glucose for immediate use and to make glycogen

Front 15

What is the rate limiting enzyme for glycogen degradation?

Back 15

glycogen phosphorylase

Front 16

What 3 things stimulate glycogen phosphorylation (glycogen degradation in muscles) during exercise?

Back 16

epinephrine, AMP, and calcium release during exercise

Front 17

What is the cost, in ATP, for adding another glucose molecule?

Back 17

2 ATP

Front 18

What are the 3 reactive steps in adding another glucose molecule to glycogen (including the enzymes?

Back 18

glucose enters the cell...a) glucose + ATP -> glucose 6-phosphate (hexokinase or glucokinase) +ADP… b) G6P -> G1P (phosphoglucomutase)… c) G1P -> UDP-glucose (UDP-glucose pyrophosphorylase)

Front 19

What impact does the fact that hexokinase has a low Km and glucokinase has a high Km for the liver's role in the body?

Back 19

the liver is involved in homeostasis to generate G6P

Front 20

While the glycogenin protein can autoglycosylate, what 2 things does it require?

Back 20

UDP-glucose and Mg-Mn

Front 21

What are the 3 steps in the degradation of glycogen in the liver (and kidneys)?

Back 21

a) glycogen + Pi -> glycogen + G1P (no high energy bonds broken here) … b) G1P -> G6P (phosphoglucomutase)… c) G6P -> Glucose (G6-phosphatase)… leaves the liver (or kidney)

Front 22

What are the 3 steps in the degradation of glycogen in muscles?

Back 22

a) glycogen + Pi -> glycogen + G1P (no high energy bonds broken here) … b) G1P -> G6P (phosphoglucomutase)… c) glycolysis

Front 23

When glucose is added to a growing glycogen polymer what enzyme catalyzes this reaction and what is lost?

Back 23

Glycogen synthase… UDP

Front 24

Which enzyme takes a linear segment and moves it?

Back 24

Tranferase

Front 25

In terms of the linkage, what does the Tranferase do?

Back 25

It breaks a ∂-1-4 linkage, moves the strand and reattaches it using a ∂-1,6 linkage, forming a new branch.

Front 26

In glycogen degradation, from glycogen(n+1) + Pi --> glycogen (n) + glucose-1-P, are high energy P bonds broken?

Back 26

No

Front 27

In glycogen degradation, what converts glucose-1-P to G-6-P?

Back 27

phosphoglucomutase

Front 28

In the liver (or kidney) what is the fate of G6P upon glycogenolysis?

Back 28

glycolysis or cellular export

Front 29

In glycogen synthesis, which enzyme starts a new branch?

Back 29

4,6-transferase

Front 30

In glycogen degradation, which enzyme breaks the 1,4 linkage? And what else is needed to make ~8 G1P?

Back 30

glycogen phophorylase… 8 Pi

Front 31

In glycogen degradation, what is the role of transferase? What is the remaining 1,6 linked glucose is removed by?

Back 31

a) transferase removes about 3-4 residues and place them at the end of another polymer using a 1,4 linkage… b) ∂-1,6 glucosidase

Front 32

What is the product of ∂-1,6-glucosidase?

Back 32

glucose

Front 33

What is the product of transferase?

Back 33

G1P

Front 34

Which enzyme converts G6P to G1P?

Back 34

phosphoglucomutase

Front 35

What is special about G1P?

Back 35

It is the intermediate point for glycogen synthesis and glycogen degradation

Front 36

Which moiety is in the central position in carbohydrate metabolism (glycogen synthesis), and is also involved in the synthesis of proteoglycans, glycoproteins, and a precursor for lactose in mammary tissue?

Back 36

UDP-glucose

Front 37

What are the regulators of glycogen stores in the liver after exercise or stress? And what effect do they have on the liver?

Back 37

(+) blood epi… (+) tissue cAMP… (Ca2+ (+)… b) they ALL cause degradation of glycogen and inhibit synthesis.

Front 38

What effect does decreased tissue cAMP have on glycogen stores in the liver?

Back 38

tissue degradation down… synthesis up… with increased cAMP the opposite would be true

Front 39

What effect do the increase in bloood epi, tissue AMP, Ca2+ calmodulin, and cAMP have on glycogen synthesis, degradation and glycolysis?

Back 39

glycolysis and degradation of glycogen are up… synthesis of glycogen are down

Front 40

Is glycogen phosphorylase, which mediates glycogen degradation, active or not active when phosphorylated?

Back 40

Active

Front 41

Is glycogen synthase I, which plays a major role in glycogen synthesis, active or not active when phosphorylated?

Back 41

Inactive

Front 42

What does the fact that PKA can phosphorylate both glycogen synthase and glycogen phosphorylase imply?

Back 42

It has opposite effects on two different pathways

Front 43

What is the step between the allosteric activation of PKA and the activation of the a cellular protein, e.g., deactivation of glycogen synthase?

Back 43

Active PKA causes the activation (via phosphorylation) of phosphorylation kinase, which activates glycogen phosphorylase, and inactivates glycogen synthase.

Front 44

What is the role of the protein phosphatase in regulation of glycogen synthesis/degradation?

Back 44

It dephosphorylates glycogen synthase

Front 45

What effect do Ca2+ (in response to nerve impulse) and epinephrine have on glycogen synthase/degradation?

Back 45

It interacts with calmodulin and phosphorylates phosphorylase kinase and ultimately leads to the phosphorylation and deactivation of glycogen synthase.

Front 46

What effect does increased AMP levels (due to muscle) have on glycogen synthase/degradation? What percentage?

Back 46

It allosterically activates glycogen phosphorylase and ultimately leads to the phosphorylation and deactivation of glycogen synthase. 80%

Front 47

What are the fuel sources for muscle from first to last?

Back 47

muscle glycogen > glucose from blood (from liver glycogen) > fatty acid oxidation from muscle TAG > fatty acid from TAG in adipose tissue

Front 48

What will a defect in G6-phosphatase (von Gierke's) Type I cause? (in liver) Why? Treatment?

Back 48

a) enlarged liver, fasting hypoglycemia, growth failure… b) glucose is not exported and G6P stimulates glycogen synthesis. C) treatment is continuous digestion of carbs

Front 49

What will a defect in amylo1,6 glucosidase (debrancher) Type II cause? (in liver)

Back 49

Fasting hypoglycemia

Front 50

What will a defect in muscle glycogen phosphorylase Type III cause? (in muscle)

Back 50

exercise-induced muscle pain, muscle weakness (muscle isozyme is defective)