Chapter 11 - glycogen synthesis and glycogenolysis

Question 1

What is glucose an energy source for?

Answer 1

Brain
Cells lacking a mitochondria like RBCs
Cells with few mitochondria
Exercising muscles 
Sudden and strenuous activity

Question 2

Where can blood glucose be obtained from?

Answer 2

Diet
Gluconeogenesis
Degradation of glycogen (glycogenolysis)

Question 3

How can glucose be stored for later use?

Answer 3

as glycogen

Question 4

Where does glycogen storage occur?

Answer 4

Liver and in skeletal muscle

Question 5

TF: Most cells store small amounts of glycogen for own use?

Answer 5

True

Question 6

Where does glycogen degradation and synthesis occur in the cell/

Answer 6

Cytosol

Question 7

From what can glycogen be made?

Answer 7

Excess blood glucose

Recycling glucogenic metabolites (lactate, glycerol, amino acids)

Question 8

What is the function of glycogen stores in the muscle?

Answer 8

Serve as a fuel reserve for synthesis of ATP

Question 9

When are muscle glycogen stores replinished?

Answer 9

After depletion by strenuous exercise

Question 10

What happens when glycogen stores are totally used up in the muscles but you still need more ATP?

Answer 10

Proteins are degraded to Amino Acids that can enter gluconeogenesis

Question 11

What are the functions of glycogen stores in the liver?

Answer 11

Maintain blood glucose concentration for 10-18 hours at a time (nocturnal fasting)

Question 12

What happens in the liver during the well fed state and during fasting?

Answer 12

When well fed, glycogen storage increases

When fasting they are depleted

Question 13

How does glycogen exist in the cytoplasm?

Answer 13

As granules

Question 14

What does the core complexes of glycogen consist of?

Answer 14

Glycogenin protein

Question 15

What end is the non reducing end in glucose?

Answer 15

C4

Question 16

How many non reducing ends are in glycogen?

Answer 16

Around 2000

Question 17

What is the relationship between branch points and terminal residues for glycogen?

Answer 17

The more branch points, the more terminal residues are available at one time

Question 18

What makes it possible for glycogen to release several glucose residues at once?

Answer 18

Highly branched structure of glycogen

Question 19

What does glycogen produce in muscles?

Answer 19

G6P

Question 20

What joins each alpha (OH below the ring) D glucose in glycogen?

Answer 20

alpha-1,4 glycosidic bonds

Question 21

How often do branch points occur in glycogen and how are they joined?

Answer 21

Every 8-10 glucosyl residues

Joined by alpha-1,6 glycosidic bonds

Question 22

What are the three steps of glycogen degradation?

Answer 22

Release of Glucose 1 phosphate from glycogen
Remodeling of glycogen for continued degradation
Conversion of glucose 1 phosphate into glucose 6 phosphate

Question 23

What does each residue cleaved from glycogen react with?

Answer 23

Phosphate to give G1P

Question 24

What kind of reaction cleaves glucose of from glycogen?

Answer 24

Phosphorolysis (glycogen phosphorylase)

Question 25

What does glycogen phosphorylase do?

Answer 25

Cleaves the alpha 1,4 linkages in the non reducing ends of glycogen

Question 26

Do you need ATP for the cleavage of glycogen?

Answer 26

No

Question 27

How are branch points removed?

Answer 27

By 2 enzymatic activities in a single enzyme Debranching enzyme that transfers a block of three residues to the non-reducing end of the chain Debranching enzyme cleaves the single remaining alpha 1,6 linked glucose (becomes a free glucose)

Question 28

What does phosphoglucomutase do?

Answer 28

Mutases transfer a side chain group throughout the same molecule In this case the mutase is moving the phosphate from C1 to C6

Question 29

What happens to G6P?

Answer 29

It is hydrolyzed by glucose 6 phosphotase (dephosphorylated) to release glucose

Question 30

Where does Glucose and Pi go after being released?

Answer 30

They are shuttled back to the cytoplasm by transporters

Question 31

What does liver glycogen phosphorylase do?

Answer 31

Breaks down glycogen into glucose 1 phosphate

Question 32

What does muscle glycogen phosphorylase do?

Answer 32

Breaks down glycogen to glucose 1 phosphate in the muscle

Question 33

What do muscle cells lack?

Answer 33

Glucose 6 phosphatase

Question 34

Where does glucose 6 phosphate go in the muscle cells since it cannot be dephosphorylated there?

Answer 34

Enters the glycolytic pathway directly and this saves 1 ATP

Question 35

What are the 3 fates of G6P?

Answer 35

Processing by the glycolytic pathway Conversion into free glucose for release into the blood (only in liver) Processing by the PPP

Question 36

Where does glycogen synthesis occur in the cell?

Answer 36

Cytosol

Question 37

TF: glycogen synthesis requires less energy than glycogen breakdown

Answer 37

False

Question 38

What must blood glucose be in order to synthesize glycogen?

Answer 38

Phosphorylated Attached to UDP Added to glycogen

Question 39

Why are there multiple steps for glycogen synthesis?

Answer 39

To allow for multiple points of regluation

Question 40

What is the first step for glycogen synthesis?

Answer 40

Glucose 6P is converted to glucose 1 P by phosphoglucomutase (transfers phosphate group)

Question 41

Where does the energy needed come from for glycogen synthesis?

Answer 41

Hydrolysis of UTP

Question 42

What is the second step for glycogen synthesis? (Stage 1)

Answer 42

Glucose 1P reacts with UTP to produce Uridine diphosphate glucose and pyrophosphate

Question 43

What does UDP glucose pyrophosphorylase do?

Answer 43

Catalyzes the interaction of G1P and UTP

Question 44

What does purophohatase do?

Answer 44

hydrolyzes PPi to Pi and PI

Question 45

What happens in stage 2 of glycogen synthesis?

Answer 45

UDPG is added to growing chain of glycogen (creates a new alpha 1,4 glycosidic bond that is catalyzed by glycogen synthase)

Question 46

When is UDP released from UDP glucose?

Answer 46

When the new alpha 1,4 glycosidic bond is formed on the nonreducing (C4) end of the already existing glycogen

Question 47

Where is the alpha 1,4 glycosidic bond formed in glycogen synthesis?

Answer 47

On the hydroxyl group of the anomeric carbon of the new glucose and the C4 non reducing end of the already existing glycogen

Question 48

What regenerates UDP to UTP?

Answer 48

UDP and ATP are used to make UTP by nucleoside diphosphate kinase

Question 49

What is the primer for glycogen?

Answer 49

Polysaccharide of glucose

Question 50

How is the primer for glycogen synthase made?

Answer 50

Glycogenin enzyme that is a dimer of two identical subunits

Question 51

What does each subunit of glycogenin generate?

Answer 51

a polysaccharide of 10-14 glucose residues in length

Question 52

What extends the primer?

Answer 52

Glycogen synthase

Question 53

What does a branching enzyme do?

Answer 53

Catalyses the reactions needed to introduce a branch point during the synthesis of glycogen

Question 54

How does the branching enzyme introduce branch points during synthesis of glycogen?

Answer 54

Transferring a segment (7 residues long) from the end of a growing chain to the branch point where it catalyzes the formation of the alpha 2,6 glycosidic linkage

Question 55

Where does the alpha 1,6 glycosidic linkage occur in glycogen?

Answer 55

At least 4 residues away from the previous branch point

Question 56

What extends branch points?

Answer 56

Glycogen synthase

Question 57

What is a major controlling factor in synthesis and breakdown of glycogen?

Answer 57

Glycogen phosphorylase

Question 58

What is glycogen phosphorylase subjected to for control?

Answer 58

Allosteric control and covalent modification

Question 59

What leads to activation of glycogen phosphorylase?

Answer 59

Phosphorylation of enzyme

Question 60

What leads to inhibition of glycogen phosphorylase?

Answer 60

Dephosphorylation of enzyme

Question 61

How is phosphorylation of glycogen phosphorylase controlled?

Answer 61

By the hormones Epinephrine and glucagon (activates breakdown of glycogen)

Question 62

What does phosphorylation do to glycogen synthase?

Answer 62

Inactivate it

Question 63

What does dephosphorylation of glycogen synthase cause?

Answer 63

Activation of the enzyme

Question 64

What is phosphorylation of glycogen synthase controlled by?

Answer 64

Stimulated by hormone signals of glucagon and epinephrine via the enzyme cAMP-dependent protein kinase

Question 65

What allosterically inhibits glycogen phosphorylase?

Answer 65

ATP and glucose 6 phosphate

Question 66

What inhibits glycogen phosphorylase in the liver?

Answer 66

Glucose

Question 67

What activates muscle glycogen phosphorylase?

Answer 67

Calcium ion release

Question 68

What activates glycogen phosphorylase?

Answer 68

AMP increase

Question 69

What allosterically activates glycogen synthase?

Answer 69

Elevated levels of glucose 6 phosphate

Question 70

What does the insulin signaling pathway do?

Answer 70

Increases glucose import into the liver Activates glycogen synthase (dephosphorylation) - increase glucose synthesis Inactivates glycogen phosphorylase (dephosphorylation)

Question 71

What does the glucagon-signaling pathway do?

Answer 71

Increases glucose export from liver Activates glycogen phosphorylase (phosphorylation)- increases glycogen degredation Deactivates glycogen sythase (phosphorylation)