Chapter 16: Glycogen Metabolism and Gluconeogenesis

Question 1

can function to stockpile glucose for later metabolic use

Answer 1

Glycogen

Question 2

When glucose is plentiful, such as immediately after a meal, glycogen synthesis what?

Answer 2

accelerates

Question 3

Under fasting conditions, most of the body’s glucose needs are met by

Answer 3

gluconeogenesis

Question 4

is an inherited condition whose major symptom is painful muscle cramps on exertion.

Answer 4

McArdle’s disease

Question 5

is a key branch point

Answer 5

Glucose-6-phosphate (G6P)

Question 6

what can Glucose-6-phosphate (G6P) be used for

Answer 6

• synthesize glycogen
• catabolized via glycolysis to yield A TP and carbon atoms (as acetyl-CoA) which can be oxidized by the citric acid cycle
• shunted through the pentose phosphate pathway to generate NADPH and/or ribose-5-phosphate

-converted to glucose for export to other tissues via the bloodstream.

Question 7

Glycogen granules are especially prominent in the cells that

Answer 7

make the greatest use of glycogen

Question 8

what cells make the greatest use of
glycogen

Answer 8

muscle and liver

Question 9

how mnay reducing ends does glycogen have?

Answer 9

one

Question 10

Glucose units are mobilized by their

Answer 10

removal from the nonreducing ends of
glycogen

Question 11

permits rapid glucose mobilization through the simultaneous release of the glucose units at the end of every branch.

Answer 11

Glycogen’s highly branched structure

Question 12

covalently binds the cofactor
pyridoxal–5′–phosphate which is a vitamin B6 derivative

Answer 12

Phosphorylase

Question 13

which state of Ser 14 is inactive

Answer 13

T -state enzyme

Question 14

The conformation of phosphorylase b is
allosterically controlled

Answer 14

the effectors AMP, ATP, and G6P

Question 15

under usual physiological conditions, the enzymatic activity of glycogen phosphorylase is largely determined by

Answer 15

its rates of phosphorylation and dephosphorylation.

Question 16

proceeds along a glycogen branch until it approaches to within 4 or 5 residues of an α

Answer 16

Phosphorolysis

Question 17

acts as an α(1→4) transglycosylase (glycosyltransferase) by transferring an
α(1→4)-linked trisaccharide unit from a limit branch of glycogen to the nonreducing end
of another branch.

Answer 17

Glycogen debranching enzyme

Question 18

converted to glucose rather than G1P .

Answer 18

About 10% of the residues in glycogen

Question 19

improves the efficiency of the debranching process.

Answer 19

Debranching enzyme has separate
active sites for the transferase and the α(1→6)-glucosidase reactions

Question 20

cannot
pass through the cell membrane

Answer 20

G6P

Question 21

resides in the endoplasmic reticulum (ER) membrane

Answer 21

G6Pase

Question 22

Glucose leaves the liver cell via a specific glucose transporter named

Answer 22

GLUT2

Question 23

The three enzymes that participate in
glycogen synthesis are

Answer 23

UDP–glucose pyrophosphorylase, glycogen synthase, and glycogen branching
enzyme.

Question 24

attaches a glucose residue donated by UDPG to the OH group of its T yr 194.

Answer 24

glycogenin,

Question 25

only extend an already existing α(1→4)-linked glucan chain.

Answer 25

Glycogen

Question 26

then extends the glucose chain by up to seven additional UDPG-donated glucose residues to form a glycogen “primer"

Answer 26

Glycogenin

Question 27

Branching to form glycogen is accomplished by

Answer 27

branching enzyme.

Question 28

each transferred segment must come from a chain of at least

Answer 28

11 residues

Question 29

and the new branch point must be at leas

Answer 29

4 residues away from other branch points.

Question 30

Both glycogen phosphorylase and glycogen synthase are under allosteric control by effectors that include

Answer 30

ATP , G6P , and AMP .

Question 31

Muscle glycogen phosphorylase is activated by

Answer 31

AMP

Question 32

Muscle glycogen phosphorylase is inhibited by

Answer 32

ATP and G6P

Question 33

when [ATP] and [G6P] are low what is favored

Answer 33

glycogen phosphorylase

Question 34

when [ATP] and [G6P] are high what is favored

Answer 34

glycogen synthesis

Question 35

Is Activated by Phosphorylation and by Ca2+ concentrations

Answer 35

Phosphorylase Kinase

Question 36

linked to the rate of muscle contraction.

Answer 36

rate of glycogen breakdown

Question 37

are linked by PKA and phosphorylase kinase

Answer 37

glycogen synthesis and breakdown

Question 38

PKA and phosphorylase kinase do what to glycogen synthase.

Answer 38

inactivate

Question 39

PKA and phosphorylase kinase do what to glycogen phosphorylase

Answer 39

activate

Question 40

is largely controlled by the polypeptide hormones insulin and glucagon acting in opposition.

Answer 40

Glycogen metabolism in the liver

Question 41

In muscles and various tissues, control is exerted by

Answer 41

insulin, epinephrine, and norepinephrine.

Question 42

critical for the liver's function in supplying glucose to tissues that depend primarily on glycolysis for their energy needs

Answer 42

Glucagon

Question 43

do not respond to glucagon because they lack the appropriate receptor.

Answer 43

Muscle cells

Question 44

are released into the bloodstream by the adrenal glands in response to stress.

Answer 44

Epinephrine and norepinephrine

Question 45

two types of receptors for Epinephrine and norepinephrine

Answer 45

the β-adrenoreceptor (β-adrenergic receptor) α-adrenoreceptor (α-adrenergic receptor)

Question 46

whose second messenger causes intracellular [Ca2+] to increase

Answer 46

α-adrenoreceptor (α-adrenergic receptor)

Question 47

which is linked to the adenylate cyclase system

Answer 47

the β-adrenoreceptor (β-adrenergic receptor)

Question 48

respond to epinephrine by breaking down glycogen for glycolysis, thereby generating ATP

Answer 48

Muscle cells

Question 49

respond to epinephrine directly and indirectly because epinephrine promotes the release of glucagon from the pancreas which activates glycogen phosphorylase and inactivates glycogen synthase

Answer 49

Liver cells

Question 50

is released from the pancreas in response to high levels of circulating glucose

Answer 50

Insulin

Question 51

increases the rate of glucose transport into the many types of cells that have both insulin receptors and insulin sensitive glucose transporters

Answer 51

Hormonal stimulation by insulin

Question 52

insulin sensitive glucose transporters called

Answer 52

GLUT4

Question 53

decreases, causing glycogen metabolism to shift from glycogen breakdown to glycogen synthesis by activating phosphoprotein phosphatase-1

Answer 53

[cAMP]

Question 54

may be a messenger to which glycogen metabolism system responds.

Answer 54

glucose

Question 54

stimulates glycogen synthesis as a result of the inhibition of glycogen synthase kinase .

Answer 54

insulin in the liver

Question 55

promotes inactivation of glycogen phosphorylase a through its conversion to phosphorylase b

Answer 55

glucose concentration

Question 56

activates glycogen synthase.

Answer 56

release of phosphoprotein phosphatase-1

Question 57

what does the liver store excess glucose as?

Answer 57

glycogen

Question 58

When dietary sources of glucose are not available and when the liver has exhausted its supply of glycogen, glucose is synthesized from noncarbohydrate precursors by

Answer 58

gluconeogenesis

Question 58

The noncarbohydrate precursors that can be converted to glucose include

Answer 58

lactate and pyruvate, citric acid cycle intermediates carbon skeletons of most amino acids

Question 58

both a precursor for gluconeogenesis and an intermediate of the citric acid cycle.

Answer 58

Oxaloacetate

Question 59

When citric acid cycle activity is low what instead enters the gluconeogenic pathway.

Answer 59

oxaloacetate

Question 60

Oxaloacetate is transported by

Answer 60

malate–aspartate shuttle system

Question 60

The generation of oxaloacetate from pyruvate or citric acid cycle intermediates occurs only in the

Answer 60

mitochondrion

Question 60

inhibits transcription of the gene for PEPCK,

Answer 60

insulin

Question 61

The net energetic cost of converting two pyruvate molecules to one glucose molecule by gluconeogenesis is

Answer 61

six ATP equivalents

Question 61

is an extremely potent allosteric activator of phosphofructokinase (PFK) and an inhibitor of fructose-1,6-bisphosphatase (FBPase).

Answer 61

Fructose-2,6-bisphosphate

Question 62

whereas high concentrations of intracellular cAMP promote the transcription of the genes for

Answer 62

EPCK, FBPase, and glucose-6-phosphatase,

Question 63

whereas high concentrations of intracellular cAMP repress the transcription of the genes for

Answer 63

glucokinase, PFK, and the PFK-2/FBPase-2 bifunctional enzyme.