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BMS 100 > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

Once Glucose is converted to Glucose-6-P what pathways can it enter?

A
  • Glycolysis
  • Pentose Phosphate Shunt
  • Glycogenesis
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2
Q

Which enzyme is needed to commit glucose 6-P to glycolysis?

A

PFK-1

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3
Q

What are the enzymes of the three irreversible reactions are also the main regulated enzymes of glycolysis

A

hexokinase and glucokinase
PFK-1
pyruvate kinase

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4
Q

What reaction does Hexokinase catalyze?

A

glucose to glucose-6-phosphate

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5
Q

Hexokinase is found in the

A

muscle

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6
Q

When cellular concentrations of glucose-6-P rise above ordinary, Hexokinase is temporarily _____________ to bring the rate of glucose-6-P into balance with its rate of utilization

A

inhibited

  • IT IS SENSITIVE TO NEED - DO WE NEED THAT GLUCOSE?
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7
Q

What reaction does PFK-1 catalyze?

A

phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate

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8
Q

what binds to the PFK-1 allosteric site to inhibit it?

A

ATP

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9
Q

what happens when ATP inhibits PFK-1 by binding to an allosteric site?

A
  • Lowers the affinity of the enzyme for fructose-6-P
  • AMP and ADP relieve the inhibition of PFK-1
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10
Q

why do AMP and ADP relieve the inhibition of PFK-1

A

As ATP is used, AMP and ADP begin to build up - therefore high levels of these tell the cell that more ATP needs to be made

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11
Q

high levels of what also inhibit PFK-1?

A

High citrate levels inhibit PFK-1
High citrate serves a signal that the cell is meeting its current needs for energy

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12
Q

what are the three ways that PFK is allosterically regulated?

A
  1. ATP - inhibit
  2. Citrate - inhibit
  3. Fructose 2,6-biphosphate - activate
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13
Q

what is the most significant allosteric regulator of PFK-1?

A

Fructose 2,6-bisphosphate

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14
Q

Fructose-2,6-bisphosphate enhances the ______ of PFK-1 for fructose-6-P. What does this stimulate?

A

affinity
Stimulates glycolysis

Inhibits FBP-1, slowing gluconeogenesis

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15
Q

what is a key intermediate in the CAC?

A

Citrate

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16
Q

Fructose 2,6-bisphosphate is formed by phosphorylating Fructose-6-P, catalyzed by ____________________

A

phosphofructokinase-2 (PFK-2)

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17
Q

What reaction does pyruvate kinase catalyze?

A

the direct transfer of phosphate from phosphoenolpyruvate (PEP) to ADP to produce ATP and pyruvate.

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18
Q

Pyruvate kinase is allosterically regulated by: Inihibtion (3)

A
  1. ATP
  2. Acetyl-CoA
  3. Fatty acids
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19
Q

Pyruvate kinase is allosterically regulated by: Activation (1)

A

Fructose 1,6-bisphosphate

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20
Q

Glycolysis is regulated hormonally by ______ and _________

A

insulin and glucagon

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21
Q

_________ promotes the transcription of glucokinase, phosphofructokinase-1, and pyruvate kinase

A

Insulin

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22
Q

________ reduces the expression
of glucokinase, PFK-1, and pyruvate kinase

A

Glucagon

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23
Q

______, _________, and ________ are converted into
glycolytic intermediates

A

Fructose, Mannose, and galactose are converted into
glycolytic intermediates

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24
Q

Which monosaccharide is metabolized faster,
glucose or fructose, why?

A

fructose
- can be more readily made into fat

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25
Q

Pyruvate can be converted either to: (3)

A

A) acetyl CoA - enter into CAC
B) Oxaloacetate - enter into GNG
C) Lactate (Cori cycle)

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26
Q

_________ is an allosteric activator of pyruvate carboxylase

A

Acetyl CoA

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27
Q

What reaction does FBP-1 catalyze?

A

catalyzing the hydrolysis of fructose-1,6-bisphosphate to fructose-6-phosphate and inorganic phosphate

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28
Q

FBP-1 is allosterically inhibited by (2)

A
  • Allosterically inhibited by AMP
  • Allosterically inhibited by Fructose 2,6-bisphosphate
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29
Q

FBP1 is found in the

A

liver

30
Q

FBP2 is found in the

A

muscle

31
Q

Gluconeogenesis is regulated hormonally by

A

insulin and glucagon

32
Q

Glucagon promotes _________ of FBP-2, lowering levels of Fructose-2,6bisP

A

activation

33
Q

Glucagon can also induce the transcription of

A

PEP carboxykinase

34
Q

Once Glucose is converted to Glucose-6-P which pathways can it enter

A
  1. Glycolysis
  2. Pentose Phosphate Shunt
  3. Glycogenesis
35
Q

Which enzyme is needed to commit glucose-6-P to glycolysis?

A

hexokinase

36
Q

The pentose phosphate shunt generates two main products:

A
  1. NADPH
  2. Ribose-5-Phosphate (“pentose phosphates)

Also generates Fructose-6-Phosphate and glyceraldehyde3-Phosphate, which can feed back into glycolysis

37
Q

what are the two phases of the Pentose Phosphate Shunt?

A

Oxidative - Irreversible reactions
Non-oxidative - Reversible reactions

38
Q

During the oxidative phase, the reaction
Glucose-6-phosphate -> Ribulose-5-phosphate generates…

A

Generates 2 NADPH

39
Q

what are the functions of the oxidative phase? (2)

A

Functions:
- Fatty acid synthesis – more to come next week
- Reduces glutathione (antioxidant)

40
Q

Glutathione is an __________. It is a 3 amino acid peptide made up of _______ - _______- ________

A

Glutathione is an antioxidant
Glycine-cystine-glutamate

41
Q

_________ regenerates glutathione by replacing the donated H’s

A

NADPH

42
Q

Pentose Phosphate Shunt is important when converting carbs to fat

A
43
Q

what neutralizes (reduces) hydrogen peroxide to water by donating H’s. NADPH will then regenerate _________ by replacing the donated H’s

A

Glutathione

44
Q

what enzyme is involved in Glucose-6-phosphate -> Ribulose-5-Phosphate

A

glucose-6-Phosphate dehydrogenase (G6PD)

45
Q

what is the rate-limiting step of the oxidative phase?

A

Glucose-6-phosphate -> Ribulose-5-Phosphate

46
Q

how is the oxidative phase regulated?

A

Regulated by ratio of NADPH:NADP+
- High NADPH: NADP+ ratio inhibits G6PD

  • Also inhibited by high levels of Acyl CoAs
  • Upregulated by insulin
47
Q

G6PD deficiency is an X-linked trait. Is it more common in men or women?

A

men

48
Q

What do you suppose Ribose-5-P can be used for?

A

R5P and its derivatives serve as precursors to many biomolecules, including DNA, RNA, ATP, coenzyme A, FAD (Flavin adenine dinucleotide), and histidine

49
Q

During the non-oxidative phase, what is ribulose-5-P converted to?

A

Ribose-5-P OR into glycolytic
intermediates

50
Q

Glucose is stored in polymeric form as glycogen
mostly in the _____ and ___________.

A

Glucose is stored in polymeric form as glycogen
mostly in the liver and skeletal muscle

muscle cells can use glucose directly BUT
the liver does not use this glucose

51
Q

High glucose/energy levels will trigger _______
synthesis

A

glycogen - Glycogenesis

52
Q

Glucose is transferred onto a growing chain of
glycogen as ____-glucose. Is this reversible or irreversible?

A

UDP
irreversible

53
Q

UDP-glucose is added to an existing strand of
glycogen by the enzyme ________________

A

glycogen synthase

54
Q

Glucose is added to the non-reducing end in what type of link?

A

alpha 1-4

55
Q

_________ catalyzes the transfer of 4-8 glucose residues to a branch point

A

Branching enzyme
The branching enzyme is also called amylo-α(1,4->1,6)
glucosyl transferase

56
Q

Glycogen synthase cannot initiate a new glycogen
chain de novo, it requires a

A

primer

57
Q

Primer contains pre-formed (alpha1-4) polyglucose
chain with at least ___ glucose residues

A

4-8

58
Q

what enzyme contains the primer and the enzyme needed to build the primer for glycogen synthesis (glycogenesis)

A

glycogenin

59
Q

Glycogenolysis is a ________ progress. It is the _______ of glycogen into glucose units. Where does this occur?

A

catabolic
Breakdown of glycogen into glucose units
Occurs in the liver and muscle

60
Q

Glucose is removed from the non-reducing ends of glycogen by the enzyme

A

Enzyme: glycogen phosphorylase

61
Q

A de-branching enzyme has two functions:

A

1) transfers the outer 3 glucose residues from the branch to another non-reducing end (leaving only 1 reside behind at the branch point)
- Aka Oligo-α(1,4)-α(1,4)-glucotransferase

2) Removes the final glucose residue in the alpha(1à6) linkage
Aka Amylo-α(1,6)-glucosidase

62
Q

Glucose-1-P is converted to glucose-6-P by the enzyme. Hint this is the same enzyme we saw in the firs step of glycogenesis

A

Enzyme: phosphoglucomutase

63
Q

The liver can then convert glucose-6-P into glucose
with the enzyme _____? Hint: This enzyme catalyzes the third bypass reaction of gluconeogenesis

A

glucose-6 phosphatase (G6Pase)
which is expressed only in the liver, kidneys, and intestine

64
Q

Muscles do not have this enzyme, why? What does the muscle do with glucose-6-P instead?

A

because they are not going to be releasing glucose

65
Q

glycogen phosphorylase

A
66
Q

Glycogen _______ and glycogen __________ are the two regulated enzymes in glycogen metabolism

A

Glycogen synthase and glycogen phosphorylase

67
Q

Glycogen synthase regulation - allosterically activaited by

A

glucose-6-P

68
Q

Glycogen phosphorylase regulation - Allosterically inhibited by? (2) and activated by _____ in the muscle only

A

inhibited by:
* Glucose-6-P
* ATP
* Free glucose (in the liver only)

activated by AMP (muscle only)

69
Q

Glycogen synthase and glycogen phosphorylase can
also be regulated by ________ modification

A

covalent

70
Q

Glycogen synthase is _________ by phosphorylation

A

de-activated

71
Q

Glycogen phosphorylase is _________ by phosphorylation. What protein catalyzes this phosphorylation?

A

activated
Phosphorylation is catalyzed initially by the same protein,
protein kinase A (PKA)

72
Q
A

BMS 100 (37 decks)

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