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BIOS4007 - Bioenergetics and Primary Metabolism > Glycolysis > Flashcards

Glycolysis Flashcards

1
Q

Define metabolism

A

The sum total of all the reactions that take place in a living cell

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2
Q

What are the reactions in metabolism for?

A
  • extract energy & materials from the environment (catabolism)
  • energy & materials used to produce new molecules (anabolism)
  • result - cell sustained & can propagate itself
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3
Q

What are reactions arranged into?

A

Pathways
- product for one reaction is the reactant (substrate) for the next

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4
Q

What is each step in a reaction pathway catalysed by?

A

catalysed by an enzyme

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5
Q

Non-spontaneous reactions are driven by …

A

coupling them to spontaneous reactions.

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6
Q

Energy is needed to …

A

drive metabolism

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7
Q

What are the 3 different arrangements of pathways?

A
  • linear
  • circular
  • spiral
    (slide 6)
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8
Q

What are intermediates in reaction pathways?

A

Temporary molecules consumed in further steps in the reaction pathway - neither reactants/products of the overall reaction.

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9
Q

What is ATP?

A
  • a molecule within the cell
  • that allows for quick & easy access to energy
  • when needed by the cell’s organelles
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10
Q

Draw the structure of ATP

A

(slide 9)
- 3 phosphate groups (triphosphate chain)
- ribose sugar
- adenine (nitrogenous base)

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11
Q

Draw the structure of ADP

A

(slide 10)
- 2 phosphate groups (diphosphate chain)
- ribose sugar
- adenine (nitrogenous base)

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12
Q

Draw the structure of AMP

A

(slide 10)
- 1 phosphate group
- ribose sugar
- adenine (nitrogenous base)

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13
Q

What is one of the common links between catabolism and anabolism?

A

ATP - used to shuttle chemical energy from catabolism to anabolism

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14
Q

What are coenzymes in metabolism?

A
  • biological oxidation/reduction agents NAD+ and FAD
  • used to shuttle energy from the favourable oxidations that take place in catabolism
  • to the unfavourable reductions that take place in anabolism (redox reactions)
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15
Q

What are the Stages of Cellular Respiration?

A
  1. Glycolysis
  2. The Krebs Cycle
  3. The Electron Transport Chain
    (all examples of metabolic pathways)
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16
Q

Is glycolysis catabolic or anabolic?

A

Catabolic pathway

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17
Q

What are the characteristics of glycolysis?

A
  • series of 10 coupled reactions
  • anaerobic
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18
Q

What are the 2 roles of gylcolysis?

A
  • supply energy
  • produce intermediates for biosynthetic pathways
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19
Q

Where does glycolysis occur?

A

Cytoplasm

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20
Q

What are the 3 stages of glycolysis?

A
  • investment stage
  • cleavage phase
  • harvesting stage
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21
Q

What is the 1st stage of glycolysis?

A

Investment stage:
- 2x ATP are consumed for each molecule of glucose
- glucose converted to fructose-1,6-bisphosphate
- glucose is trapped inside the cell and at the same time converted to an unstable form that can be readily cleaved into 3-C units

(slide 16)

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22
Q

What is the 2nd stage of glycolysis?

A

Cleavage stage:
- fructose-1,6-bisphosphate is cleaved into …
- 2x 3-C units of glyceraldehyde-3-phosphate

(slide 16)

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23
Q

What is the 3rd stage of glycolysis?

A

Harvesting stage:
- 4x ATP and 2x NADH are gained from each molecule of glucose
(- this ATP is a result of substrate-level phosphorylation)
- glyceraldehyde-3-phosphate is oxidized to pyruvate

(slide 16)

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24
Q

What is reaction 1 of glycolysis?

A

Phosphorylation of glucose to glucose 6-phosphate

glucose + ATP → G-6P + ADP + H+
- enzyme: hexokinase

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25
Q

What reaction type is reaction 1?

A

Phosphoryl transfer

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26
Q

What enzyme is used in reaction 1 of glycolysis?

A

Hexokinase
- has a low Km for glucose; thus, once glucose enters the cell, it gets phosphorylated

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27
Q

What happens in reaction 1 of glycolysis?

A

Reaction requires energy
- so coupled to the hydrolysis of ATP to ADP and Pi

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28
Q

Is reaction 1 of glycolysis reversible or irreversible?

A

Irreversible step
- ∴ glucose gets trapped inside cell
- (glucose transporters transport only free glucose, not phosphorylated glucose)

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29
Q

What is reaction 2 of glycolysis?

A

Isomerization of glucose 6-phosphate to fructose 6-phosphate

G-6P ⇌ F-6P

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30
Q

What reaction type is reaction 2?

A

Isomerization

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31
Q

What enzyme is used in reaction 2 of glycolysis?

A

phosphoglucose isomerase

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32
Q

What happens in reaction 2 of glycolysis?

A

Aldose sugar converted into the keto- isoform

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33
Q

Is reaction 2 of glycolysis reversible or irreversible?

A

Reversible reaction
- F-6P quickly consumed
- and the forward reaction is favoured

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34
Q

What is reaction 3 of glycolysis?

A

Phosphorylation of the hydroxyl group on C1 (of F-6P), forming fructose 1,6-bisphosphate

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35
Q

What reaction type is reaction 3?

A

Phosphoryl transfer

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36
Q

What enzyme is used in reaction 3 of glycolysis?

A

phosphofructokinase
- allosteric enzyme regulates pace of glycolysis

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37
Q

What happens in reaction 3 of glycolysis?

A

Reaction is coupled to the hydrolysis of an ATP to ADP and Pi

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38
Q

Is reaction 3 of glycolysis reversible or irreversible?

A

irreversible reaction of the glycolytic pathway

39
Q

What is reaction 4 of glycolysis?

A

Begins Stage 2
fructose-1,6-bisphosphate ⇌ dihydroxyacetone phosphate + glyceraldehyde 3-phosphate

F-1,6-BP ⇌ DHAP + GAP

40
Q

What reaction type is reaction 4?

A

Aldol cleavage

41
Q

What enzyme is used in reaction 4 of glycolysis?

A

Aldolase

42
Q

What happens in reaction 4 of glycolysis?

A

Fructose-1,6-bisphosphate splits into:
- 2x 3-carbon molecules
- one aldehyde
- one ketone:
dihyroxyacetonephosphate (DHAP) and glyceraldehyde 3-phosphate (GAP)

43
Q

What is reaction 5 of glycolysis?

A

dihydroxyacetone phosphate ⇌ glyceraldehyde 3-phosphate

44
Q

What reaction type is reaction 5?

A

Isomerization

45
Q

What enzyme is used in reaction 5 of glycolysis?

A

triose phosphate isomerase

46
Q

What happens in reaction 5 of glycolysis?

A
  • DHAP and GAP are isomers of each other
  • so readily inter-convert by the enzyme
  • GAP is a substrate for the next step in glycolysis
  • so all of the DHAP is eventually depleted
  • ∴ 2 molecules of GAP are formed from each molecule of glucose
47
Q

What is reaction 6 of glycolysis?

A

Begins Stage 3.
- GAP is dehydrogenated by enzyme (GAPDH)
- NAD+ is reduced

GAP + NAD+ + Pi ⇌ 1,3-BPG + NADH + H+

48
Q

What reaction type is reaction 6?

A

Phosphorylation coupled to oxidation

49
Q

What enzyme is used in reaction 6 of glycolysis?

A

glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

50
Q

What happens in reaction 6 of glycolysis?

A
  • Up to this step, 2 molecules of ATP were required for each molecule of glucose being oxidized
  • Since there are 2 GAP molecules generated from each glucose, each of the remaining reactions occur twice for each glucose molecule being oxidized
51
Q

What is reaction 7 of glycolysis?

A

1,3-BPG + ADP + H+ ⇌ 3-Phosphoglycerate + ATP

52
Q

What reaction type is reaction 7?

A

Phosphoryl transfer

53
Q

What enzyme is used in reaction 7 of glycolysis?

A

phosphoglycerate kinase

54
Q

What happens in reaction 7 of glycolysis?

A

1,3-BPG has:
- a mixed anhydride
- a high energy bond at C1
- this high energy bond is hydrolysed to a carboxylic acid
- and the energy released is used to generate ATP from ADP

55
Q

What is reaction 8 of glycolysis?

A

3-Phosphoglycerate ⇌ 2-Phosphoglycerate

56
Q

What reaction type is reaction 8?

A

Phosphoryl shift

57
Q

What enzyme is used in reaction 8 of glycolysis?

A

phosphoglycerate mutase

58
Q

What happens in reaction 8 of glycolysis?

A

The phosphate shifts from C3 to C2 to form 2-phosphoglycerate

59
Q

What is reaction 9 of glycolysis?

A

2-Phosphoglycerate ⇌ Phosphenolpyruvate + H2O

60
Q

What reaction type is reaction 9?

A

Dehydration

61
Q

What enzyme is used in reaction 9 of glycolysis?

A

enolase (lyase)

62
Q

What happens in reaction 9 of glycolysis?

A
  • dehydration catalyzed by enolase (a lyase)
  • H2O molecule removed to form phosphoenolpyruvate
  • which has a double bond between C2 and C3
63
Q

What is reaction 10 of glycolysis?

A

Phosphoenolpyruvate + ADP + H+ → Pyruvate + ATP

64
Q

What reaction type is reaction 10?

A

Phosphoryl transfer

65
Q

What enzyme is used in reaction 10 of glycolysis?

A

pyruvate kinase

66
Q

What happens in reaction 10 of glycolysis?

A
  • Enolphosphate is a high energy bond
  • hydrolyzed to form the enolic form of pyruvate with the synthesis of ATP
  • Enol pyruvate quickly changes to keto pyruvate which is far more stable.
67
Q

State the reactants/products of each step of glycolysis

A
  • glucose
  • glucose 6-phosphate
  • fructose 6-phosphate
  • fructose 1,6-biphosphate
  • dihydroxyacetone ⇌ glyceraldehyde 3-phosphate
  • 1,3-Biphosphoglycerate
  • 3-Phosphoglycerate
  • 2-Phosphoglycerate
  • Phosphoenolpyruvate
  • Pyruvate
68
Q

What is Gibbs free energy ΔG?

A

Thermodynamic property that measures the amount of energy available to do useful work in a system (at constant T & P)
- used to determine whether a reaction is spontaneous or non-spontaneous

69
Q

What are the ΔG values of a spontaneous and non-spontaneous reaction?

A

spontaneous = ΔG<0
non-spontaneous = ΔG>0

70
Q

What are the ΔG values of a spontaneous and non-spontaneous reaction?

A

spontaneous = ΔG<0
non-spontaneous = ΔG>0

71
Q

When does a negative ΔG occur?

A
  • ΔH is negative
    and/or
  • ΔS is positive
72
Q

What does ΔG tell us about the direction of a reaction?

A

Tells us which direction a reaction will favour
- does not mean it will go to completion, rather to equilibrium

73
Q

What does a negative and positive ΔH mean?

A

-ΔH = exothermic
+ΔH = endothermic

74
Q

What does a negative and positive ΔG mean?

A

-ΔG = reaction feasible
+ΔG = reaction not feasible

75
Q

What does it mean when ΔG = 0?

A

reaction is in equilibrium

76
Q

What happens as ΔG gets more negative in glycolysis?

A
  • ΔG gets more negative
  • moves further away from equilibrium
  • harder to reverse
77
Q

Why do we need to control pathways?

A
  • so opposing pathways don’t run at same time
  • desired product is not made in sufficient quantities
  • waste ATP
  • important to stop futile cycle
78
Q

What is the enzyme hexokinase regulated by?

A

excess glucose-6-phosphate (G6P)

79
Q

How is hexokinase regulated by G6P?

A
  • G6P accumulates in cell (meaning there is enough glucose)
  • feedback inhibition of hexokinase
  • until G6P is consumed
80
Q

What is the reverse reaction pathway of glycolysis called?

A

gluconeogenesis

81
Q

What is the rate-limiting step of glycolysis?

A

phosphofructokinase step
(step 3)

82
Q

What activates and inhibits the phosphofructokinase enzyme?

A

activates: high AMP/ADP levels
inhibits: high ATP levels

83
Q

How is phosphofructokinase regulated by feed-back inhibition by citrate?

A
  • citrate = allosteric regulator of PFK
  • overproduction of citrate = more than enough ATP
  • negative feedback mechanism of citrate inhibits PFK
  • this prevents overproduction of ATP in 3rd reaction of glycolysis
84
Q

Define allosteric

A
  • inhibition or activation of an enzyme
  • by a small regulatory molecule
  • that interacts at a site (allosteric site) other than the active site (at which catalytic activity occurs)
85
Q

Give an example of allosteric feed-forward activation involving phosphofructokinase

A
  • positive effector of phosphofructokinase = fructose-2,6-bisphosphate (F-2,6-BP)
  • formed by hormone-stimulated phosphorylation of F-6-P
86
Q

When is pyruvate kinase regulated?

A

If glycolysis gets past phosphofructokinase step

87
Q

When is pyruvate kinase activity inhibited?

A

Under low glucose conditions by covalent phosphorylation

88
Q

What drives the pyruvate kinase reaction forwards?

A

If fructose-1,6-bisphosphate is formed
- acts as an allosteric feedforward activator

89
Q

What are positive and negative effectors in the regulation of pyruvate kinase?

A
  • positive = AMP and ADP
  • negative = ATP (binds to allosteric sites)
90
Q

What is a negative effector of catabolism?

A

alanine (amino acid derived from pyruvate)

91
Q

What do alanine levels signal?

A

Alanine levels signal the anabolic state of a cell

92
Q

What do high alanine levels indicate?

A
  • the cell has enough starting material for anabolic reactions
  • so catabolism can be paused
93
Q

What are the 3 ‘fates’ of pyruvate produced by glycolysis?

A
  • anaerobic (lactic acid fermentation)
  • aerobic oxidation
  • anaerobic (alcoholic fermentation)

BIOS4007 - Bioenergetics and Primary Metabolism (6 decks)

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