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Biochemistry > Chapter 16: Glycogen Metabolism and Gluconeogenesis > Flashcards

Chapter 16: Glycogen Metabolism and Gluconeogenesis Flashcards

1
Q

can function to stockpile glucose for later metabolic use

A

Glycogen

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2
Q

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

A

accelerates

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3
Q

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

A

gluconeogenesis

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4
Q

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

A

McArdle’s disease

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5
Q

is a key branch point

A

Glucose-6-phosphate (G6P)

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6
Q

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

A
  • 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.

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7
Q

Glycogen granules are especially prominent in the cells that

A

make the greatest use of glycogen

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8
Q

what cells make the greatest use of
glycogen

A

muscle and liver

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9
Q

how mnay reducing ends does glycogen have?

A

one

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10
Q

Glucose units are mobilized by their

A

removal from the nonreducing ends of
glycogen

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11
Q

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

A

Glycogen’s highly branched structure

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12
Q

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

A

Phosphorylase

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13
Q

which state of Ser 14 is inactive

A

T -state enzyme

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14
Q

The conformation of phosphorylase b is
allosterically controlled

A

the effectors AMP, ATP, and G6P

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15
Q

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

A

its rates of phosphorylation and dephosphorylation.

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16
Q

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

A

Phosphorolysis

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17
Q

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.

A

Glycogen debranching enzyme

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18
Q

converted to glucose rather than G1P .

A

About 10% of the residues in glycogen

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19
Q

improves the efficiency of the debranching process.

A

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

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20
Q

cannot
pass through the cell membrane

A

G6P

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21
Q

resides in the endoplasmic reticulum (ER) membrane

A

G6Pase

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22
Q

Glucose leaves the liver cell via a specific glucose transporter named

A

GLUT2

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23
Q

The three enzymes that participate in
glycogen synthesis are

A

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

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24
Q

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

A

glycogenin,

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25
Q

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

A

Glycogen

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26
Q

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

A

Glycogenin

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27
Q

Branching to form glycogen is accomplished by

A

branching enzyme.

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28
Q

each transferred segment must
come from a chain of at least

A

11 residues

29
Q

and the new branch point must be at leas

A

4 residues away from other branch points.

30
Q

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

A

ATP , G6P , and AMP .

31
Q

Muscle glycogen phosphorylase is activated by

A

AMP

32
Q

Muscle glycogen phosphorylase is inhibited by

A

ATP and G6P

33
Q

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

A

glycogen phosphorylase

34
Q

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

A

glycogen synthesis

35
Q

Is Activated by Phosphorylation
and by Ca2+ concentrations

A

Phosphorylase Kinase

36
Q

linked to the rate of muscle contraction.

A

rate of glycogen breakdown

37
Q

are linked by PKA and phosphorylase kinase

A

glycogen synthesis and breakdown

38
Q

PKA and phosphorylase kinase do what to glycogen synthase.

A

inactivate

39
Q

PKA and phosphorylase kinase do what to glycogen phosphorylase

A

activate

40
Q

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

A

Glycogen metabolism in the liver

41
Q

In muscles and various tissues, control is exerted by

A

insulin, epinephrine, and norepinephrine.

42
Q

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

A

Glucagon

43
Q

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

A

Muscle cells

44
Q

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

A

Epinephrine and norepinephrine

45
Q

two types of receptors for Epinephrine and norepinephrine

A

the β-adrenoreceptor (β-adrenergic receptor)

α-adrenoreceptor (α-adrenergic receptor)

46
Q

whose second messenger causes intracellular [Ca2+] to increase

A

α-adrenoreceptor (α-adrenergic receptor)

47
Q

which is linked to the adenylate cyclase system

A

the β-adrenoreceptor (β-adrenergic receptor)

48
Q

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

A

Muscle cells

49
Q

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

A

Liver cells

50
Q

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

A

Insulin

51
Q

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

A

Hormonal stimulation by insulin

52
Q

insulin sensitive glucose transporters called

A

GLUT4

53
Q

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

A

[cAMP]

54
Q

may be a messenger to which glycogen metabolism system responds.

A

glucose

54
Q

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

A

insulin in the liver

55
Q

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

A

glucose concentration

56
Q

activates glycogen synthase.

A

release of phosphoprotein phosphatase-1

57
Q

what does the liver store excess glucose as?

A

glycogen

58
Q

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

A

gluconeogenesis

58
Q

The noncarbohydrate precursors that can be converted to glucose include

A

lactate and pyruvate,

citric acid cycle intermediates

carbon skeletons of most amino acids

58
Q

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

A

Oxaloacetate

59
Q

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

A

oxaloacetate

60
Q

Oxaloacetate is transported by

A

malate–aspartate shuttle system

60
Q

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

A

mitochondrion

60
Q

inhibits transcription of the gene for PEPCK,

A

insulin

61
Q

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

A

six ATP equivalents

61
Q

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

A

Fructose-2,6-bisphosphate

62
Q

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

A

EPCK, FBPase, and glucose-6-phosphatase,

63
Q

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

A

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

Biochemistry (17 decks)

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