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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
what hormones regulates gluconeogenesis?
insulin and glucagon
26
how does glucagon regulate gluconeogenesis?
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
what is pentose phosphate shunt?
alternative metabolic pathway for glucose that "shunts" molecules into and out of glycolysis
28
what are the products of pentose phosphate shunt?
- NADPH - Ribose-5-phosphate (pentose phosphate) - also generate fructose-6-phosphate and glyceraldehyde-2-phosphate which can feedback into glycolysis
29
what is the oxidative phase of pentose phosphate shunt?
glucose-6-phosphate -> ribulose-5-phosphate and generates 2 NADPH
30
Glutathione is an antioxidant, what regenerates glutathione?
NADPH regenerates glutathione by replacing the donated H's
31
what is the rate-limiting step of the oxidative phase of pentose phosphate shunt
glucose-6-phosphate -> 6-phosphoglucono-sigma-lactone
32
what enzyme is used for converting glucose-6-phosphate -> ribulose-5-phosphate
glucose-6-phosphate dehydrogenase (G6PD)
33
what regulates glucose-6-phosphate dehydrogenase (G6PD)
ratio of NADPH:NADP+, high NADPH:NADP+ ratio inhibits G6PD - also inhibited by high levels of Acyl CoAs - upregulated by insulin
34
G6PD deficieny is an
X-linked trait
35
what is the results in G6PD deficiency
results in hemolutic anemia when an individual is exposed to oxidant stress
36
what happens in non-oxidative phase
riboluse-5-phosphate is converted to ribose-5-phosphate or into glycotic intermediates
37
glucose is stored in polymeric form as glycogen mostly in the ?
liver and skeletal muscle
38
glucose can be rapidly delivered to the bloodstream when needed by what?
degradation of glycogen (glycogenolysis)
39
for glycogenesis, glucose is transferred onto a growing chain of glycogen as what?
UDP-glucose
40
what enzyme adds the UDP-glucose to an existing strand of glycogen by the enzyme?
glycogen synthase
41
what type of bond is it when glucose is added to the glycogen strand?
glycosidic bond
42
glycogen synthase cannot initiate a new glycogen chain, it requires a primer called?
glycogenesis primer
43
glycogenesis primer contains?
contains pre-formed (alpha 1-4) polyglucose chain with at least 4-8 glucose residues
44
the glycogenesis primer is found within what?
glycogenin
45
glycogenolysis is a catabolic or anabolic process
catabolic process
46
glycogenolysis is
the breakdown of glycogen into glucose units
47
where does glycogenolysis occurs
in the liver and muscle
48
what is the enzyme for glycogenolysis?
glycogen phosphorylase
49
what does glycogen phosphorylase do?
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
what is a limit dextrin
when the glycogen chain is degraded to within 4 units of a branch point
51
what do the de-branching enzyme do
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
what is the enzyme that converts glucose-1-phosphate to glucose-6-phosphate
phosphoglycomutase
53
what are the 2 enzymes that regulate glycogen metabolism
glycogen synthase and glycogen phosphorylase
54
glycogen synthase is allosterically activated by?
glucose-6-phosphate
55
glycogen phosphorylase is allosterically inhibited by:
- glucose-6-phosphate - ATP - free glucose (in the liver only)
56
glycogen phosphorylase is allosterically activated by?
AMP (muscle only)
57
glycogen synthase is ? by phosphorylation
de-activated
58
glycogen phosphorylase is ? by phosphorylation
activated
59
phosphorylation of glycogen synthase or glycogen phosphorylase is catalyzed by what enzyme
protein kinase A
60
for glycogen metabolism, in the presence of glucagon what happens?
§ Glucagon binds to its GCPR § Galphasubunit activates adenylyl cyclase -> cAMP levels rise § PKA phosphorylates glycogen synthase, rendering it inactive - glycogenesis is inhibited
61
for glycogen metabolism, in the presence of glucagon what happens? (2)
- PKA phosphorylates glycogen phosphorylase kinase, rendering it active - Glycogen phosphorylase kinase phosphorylates glycogen phosphorylase, rendering it active - Glycogenolysis is promoted
62
for glycogen metabolism, in the presence of insulin what happens?
- 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
for glycogen metabolism, in the presence of insulin what happens? (2)
- 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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