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BMS test 2 > Biochem: Carbo Metabolism > Flashcards

Biochem: Carbo Metabolism Flashcards

1
Q

once glucose is converted to glucose-6-phosphate it can enter several pathways:

A
  • glycolysis
  • pentose phosphate shunt
  • glycogenesis
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2
Q

what are the enzymes of the 3 irreversible reactions for glycolysis

A
  • hexokinase
  • PFK
  • Pyruvate kinase
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3
Q

what reaction does hexokinase catalyze?

A

glucose -> glucose-6-phosphate

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4
Q

how is hexokinase regulated?

A

reversibly regulated by glucose-6-phosphate (product inhibition)

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5
Q

what reaction does PFK-1 catalyze?

A

fructose-6-phosphate -> fructose-1,6-bisphosphate

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6
Q

what inhibits PFK-1?

A

ATP and Citrate

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7
Q

how does ATP regulate PFK-1?

A

ATP inhibits PFK-1 by binding to an allosteric site, lowering the affinity of the enzyme for fructose-6-phosphate

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8
Q

how does citrate regulate PFK-1?

A

citrate is key intermediate in the CAC, high citrate levels inhibit PFK-1

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9
Q

how does fructose 2,6 - bisphosphate regulate PFK-1?

A

fructose-2,6-bisphosphate enhances the affinity of PFK-1 for fructose-6-phosphate

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10
Q

what activates PFK-1

A

fructose 2,6 bisphosphate

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11
Q

how is fructose-2,6-bisphosphate formed?

A

by phosphorylating fructose-6-phosphate, catalyzed by phosphofructokinase-2 (PFK-2)

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12
Q

what reaction does pyruvate kinase catalyze?

A

phosphoenopyruvate -> pyruvate

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13
Q

what inhibits pyruvate kinase?

A
  • ATP
  • Acetyl-CoA
  • fatty acids
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14
Q

what activates pyruvate kinase?

A

fructose 1,6- bisphosphate

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15
Q

what hormones regulate glycolysis?

A

insulin and glucagon

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16
Q

how does insulin regulate glycolysis?

A

insulin promotes the transcription of hexokinase, phosphofructokinase-1, and pyruvate kinase

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17
Q

how does glucagon regulate glycolysis?

A

glucagon reduces the expression of hexokinase, PFK-1, and pyruvate kinase
glucagon also promotes the activation of FBP-2 which inhibits PFK-2

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18
Q

sugars can also convert into glycolytic intermediates like

A

fructose

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19
Q

fructose turn into what to create glycolytic intermediates

A

fructose-1-phosphate and then DHAP + glyceraldehyde

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20
Q

what is the by-pass reaction 1 for gluconeogenesis?

A

pyruvate -> oxaloacetate with pyruvate carboxylase and then oxaloavetate -> phosphoenolpyruvate with phosphoenolpyruvate carboxykinase

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21
Q

what is the by-pass reaction 2 for gluconeogenesis?

A

fructose 1,6-bisphosphate -> fructose 6-phosphate with fructose 1,6-bisphosphatase

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22
Q

what is an allosteric activator of pyruvate carboxylase?

A

acetyl-CoA

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23
Q

what reaction does fructose bisphosphatase-1 catalyze? (FBP-1)

A

fructose 1,6-bisphosphate -> fructose 6-phosphate

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24
Q

what inhibites FBP-1

A

AMP and fructose 2,6-bisphosphate

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25
Q

what hormones regulates gluconeogenesis?

A

insulin and glucagon

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26
Q

how does glucagon regulate gluconeogenesis?

A

glucagon promotes activation of FBP-2, lowering levels of fructose-2,6 bisphosphate so more gluconeogenesis happens, also induces the transcription of PEP carboxykinase

27
Q

what is pentose phosphate shunt?

A

alternative metabolic pathway for glucose that “shunts” molecules into and out of glycolysis

28
Q

what are the products of pentose phosphate shunt?

A
  • NADPH
  • Ribose-5-phosphate (pentose phosphate)
  • also generate fructose-6-phosphate and glyceraldehyde-2-phosphate which can feedback into glycolysis
29
Q

what is the oxidative phase of pentose phosphate shunt?

A

glucose-6-phosphate -> ribulose-5-phosphate and generates 2 NADPH

30
Q

Glutathione is an antioxidant, what regenerates glutathione?

A

NADPH regenerates glutathione by replacing the donated H’s

31
Q

what is the rate-limiting step of the oxidative phase of pentose phosphate shunt

A

glucose-6-phosphate -> 6-phosphoglucono-sigma-lactone

32
Q

what enzyme is used for converting glucose-6-phosphate -> ribulose-5-phosphate

A

glucose-6-phosphate dehydrogenase (G6PD)

33
Q

what regulates glucose-6-phosphate dehydrogenase (G6PD)

A

ratio of NADPH:NADP+, high NADPH:NADP+ ratio inhibits G6PD
- also inhibited by high levels of Acyl CoAs
- upregulated by insulin

34
Q

G6PD deficieny is an

A

X-linked trait

35
Q

what is the results in G6PD deficiency

A

results in hemolutic anemia when an individual is exposed to oxidant stress

36
Q

what happens in non-oxidative phase

A

riboluse-5-phosphate is converted to ribose-5-phosphate or into glycotic intermediates

37
Q

glucose is stored in polymeric form as glycogen mostly in the ?

A

liver and skeletal muscle

38
Q

glucose can be rapidly delivered to the bloodstream when needed by what?

A

degradation of glycogen (glycogenolysis)

39
Q

for glycogenesis, glucose is transferred onto a growing chain of glycogen as what?

A

UDP-glucose

40
Q

what enzyme adds the UDP-glucose to an existing strand of glycogen by the enzyme?

A

glycogen synthase

41
Q

what type of bond is it when glucose is added to the glycogen strand?

A

glycosidic bond

42
Q

glycogen synthase cannot initiate a new glycogen chain, it requires a primer called?

A

glycogenesis primer

43
Q

glycogenesis primer contains?

A

contains pre-formed (alpha 1-4) polyglucose chain with at least 4-8 glucose residues

44
Q

the glycogenesis primer is found within what?

A

glycogenin

45
Q

glycogenolysis is a catabolic or anabolic process

A

catabolic process

46
Q

glycogenolysis is

A

the breakdown of glycogen into glucose units

47
Q

where does glycogenolysis occurs

A

in the liver and muscle

48
Q

what is the enzyme for glycogenolysis?

A

glycogen phosphorylase

49
Q

what does glycogen phosphorylase do?

A

it cleaves alpha (1-4) linkages from the non-reducing ends until 4 units away from a branch point, the glucose is released as glucose-1-phosphate

50
Q

what is a limit dextrin

A

when the glycogen chain is degraded to within 4 units of a branch point

51
Q

what do the de-branching enzyme do

A
  1. transfers the outer 3 glucose residues from the branch to another non-reducing end leaving only 1 reside at the branch point
    the enzyme is oligo-alpha (1,4)-alpha (1,4)-glucotransferase
  2. removes the final glucose residue in the alpha (1->6) linkage, the enzyme is amylo-alpha (1,6)-glucosidase
52
Q

what is the enzyme that converts glucose-1-phosphate to glucose-6-phosphate

A

phosphoglycomutase

53
Q

what are the 2 enzymes that regulate glycogen metabolism

A

glycogen synthase and glycogen phosphorylase

54
Q

glycogen synthase is allosterically activated by?

A

glucose-6-phosphate

55
Q

glycogen phosphorylase is allosterically inhibited by:

A
  • glucose-6-phosphate
  • ATP
  • free glucose (in the liver only)
56
Q

glycogen phosphorylase is allosterically activated by?

A

AMP (muscle only)

57
Q

glycogen synthase is ? by phosphorylation

A

de-activated

58
Q

glycogen phosphorylase is ? by phosphorylation

A

activated

59
Q

phosphorylation of glycogen synthase or glycogen phosphorylase is catalyzed by what enzyme

A

protein kinase A

60
Q

for glycogen metabolism, in the presence of glucagon what happens?

A

§ Glucagon binds to its GCPR
§ Galphasubunit activates adenylyl cyclase -> cAMP levels rise
§ PKA phosphorylates glycogen synthase, rendering it inactive
- glycogenesis is inhibited

61
Q

for glycogen metabolism, in the presence of glucagon what happens? (2)

A
  • PKA phosphorylates glycogen phosphorylase kinase, rendering it active
  • Glycogen phosphorylase kinase phosphorylates glycogen phosphorylase, rendering it active
  • Glycogenolysis is promoted
62
Q

for glycogen metabolism, in the presence of insulin what happens?

A
  • Insulin promotes the breakdown of cAMP and thus inactivation of PKA
  • Insulin activates protein phosphatase 1, which removes the phosphate group from glycogen synthase, rendering it active
  • Glycogenesis is promoted
63
Q

for glycogen metabolism, in the presence of insulin what happens? (2)

A
  • Insulin promotes the breakdown of cAMP and thus inactivation of PKA
  • Insulin activates protein phosphatase 1, which removes the phosphate group from:
    ○ Glycogen phosphorylase kinase & Glycogen phosphorylase, rendering them both inactive
  • Glycogenolysis is inhibited

BMS test 2 (11 decks)

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