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BIOCH 200 > 9 Glycolysis > Flashcards

9 Glycolysis Flashcards

1
Q

Glycolysis is a _________ pathway (catabolic or anabolic?)

A

Glycolysis is a catabolic pathway:

converting one glucose into two molecules of pyruvate

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2
Q

Glycolysis generates what two cofactors?

A

ATP directly

NADH from oxidation of metabolites

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3
Q

Glucose is a ____ carbon compound with one _____ group and five _____ groups

Structure of Glucose may be depicted in many ways

A

Glucose is a 6 carbon compound with one aldehyde group and five hydroxyl groups

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4
Q

Glycolysis typically operates under _____ conditions to generate ATP.

A

Glycolysis typically operates under anaerobic conditions to generate ATP.

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5
Q

Glycolysis can also operate aerobically to produce ______

A

Glycolysis can also operate aerobically ​to produce NADH

  • manner of NADH reoxidation
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6
Q

Where does glycolysis occur and what does it involve?

A

Glycolysis involves 10 enzyme-catalyzed reactions that occur in the cytosol to break down one glucose (6C) into 2 pyruvate (3C)

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7
Q

What are the two Stages of glycolysis?

A
  • Stage 1: Energy Investment
    • “hexoses phase”
    • glucose needs to be activated
    • energy (ATP) is consumed
    • Involves hexose (6C sugars)
  • Stage 2: Energy Payout
    • Energy is harvested in the form of ATP
    • NADH is also generated
    • Involves triose (3 C) sugars
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8
Q

What are the four reactions that occur in the Energy investment phase (phase 1) of Glycolysis?

A

Glucose

↓

glucose-6-phosphate (G6P)

⇅

fructose-6-phosphate (F6P)

↓

fructose-1,6-bisphosphate

↓ (1) ↓(2)

dihydroxyacetone phosphate ⇄ glyceraldehyde-3-phosphate (GAP) (x2)

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9
Q

What are the 5 reactions that occur in the energy payout phase of glycolysis (phase 2)

A

glyceraldehyde-3-phosphate

⇅

1,3-bisphosphoglycerate

⇅

3-phosphoglycerate

⇅

2-phosphoglycerate

⇅

phosphoenolpyruvate

↓

pyruvate

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10
Q

What catalyses the reaction of glucose to glucose-6-phosphate?

A

Hexokinase, and glucokinase

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11
Q

What catalyses the reaction of fructose-6-phosphate to Fructose 1,6-bisphosphate?

A

Phosphofructokinase-1 (PFK-1)

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12
Q

What catalyses the reaction of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate?

A

Glyceraldehyde-3-phosphate dehydrogenase

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13
Q

What catalyzes the reaction of phosphoenolpyruvate to Pyruvate?

A

Pyruvate kinase

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14
Q

How many ATP are consumed in the energy investment phase?

A

2 ATP for every glucose

Energy investment phase includes the conversion of Glucose to Glyceraldehyde-3-phosphate (GAP)

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15
Q

Reaction one:

Glucose to glucose-6-phosphate

  • reversible?
  • Catalyzed by?
  • Coupled?
  • Type of reaction?
  • Regulated?
A

Reaction one:

Glucose + ATP -> glucose-6-phosphate (G6P) + ADP + H+

  • reversible?
    • No - Irreversible
      • Large negative delta G
  • Catalyzed by?
    • Hexokinase (6C phosphate transfer)
  • Coupled?
    • Yes - consumes ATP (ATP is reactant)
  • Type of reaction?
    • Phosphate transfer (Pi from ATP to glucose)
  • Regulated?
    • Yes, not rate limiting
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16
Q

Reaction 2:

Glucose-6-Phosphate (G6P) to Fructose-6-phosphate (F6P)

  • reversible?
  • Coupled?
  • Type of reaction?

Fructose is a _______ and is a structural isomer of glucose

A

Reaction 2:

Glucose-6-Phosphate (G6P) to Fructose-6-phosphate (F6P)

  • reversible?
    • Yes (delta G approx 0)
  • Coupled?
    • No, no ATP consumed (or produced)
  • Type of reaction?
    • Isomerization
      • Aldehyde to ketone

Fructose is a ketohexose and is a structural isomer of glucose

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17
Q

Reaction 3:

Fructose-6-phosphate to fructose 1,6-bisphosphate

  • Reversible?
  • ATP used (coupled) or consumed?
  • Type of Reaction
  • Catalyzed by?
  • Regulated?
A

Reaction 3:

Fructose-6-phosphate + ATP -> fructose 1,6-bisphosphate + ADP + H+

  • Reversible?
    • No Irreversible (delta G large negative)
  • ATP used (coupled) or consumed?
    • ATP used - reactant = coupled
  • Type of Reaction
    • Phosphate transfer reaction
  • Catalyzed by?
    • phosphofructokinase-1 (PFK-1)
  • Regulated?
    • Yes
    • Rate Limiting
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18
Q

What is the rate-limiting step of glycolysis?

What catalyzes this reaction?

A

Reaction 3:

Fructose-6-phosphate to fructose 1,6-bisphosphate catalyzed by PFK-1 (phosphofructokinase-1)

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19
Q

Reaction 4:

The Lysis Reaction

Fructose 1,6-bisphosphate (F-1,6-BP) to _________ and ________

A

Reaction 4:

The Lysis Reaction

Fructose 1,6-bisphosphate (F-1,6-BP) to dihydroxyacetone phosphate (DHAP)** and **Glyceraldehyde-3-Phosphate (GAP)

DHAP and GAP are isomers of each other

  • DHAP = ketone to GAP=aldehyde
  • Elimination reaction
  • Reversible reaction
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20
Q

Reaction 5:

Dihydroxyacetone phosphate (DHAP) to Glyceraldehyde-3-Phosphate (GAP)

  • Type of Reaction?
  • Reversible?
A

Reaction 5:

Dihydroxyacetone phosphate (DHAP) to Glyceraldehyde-3-Phosphate (GAP)

  • Type of Reaction?
    • Isomerization
  • Reversible?
    • Yes, delta G close to 0
  • DHAP ⇄ GAP
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21
Q

During glycolysis, 2 molecules of Glyceraldehyde-3-phosphate are produced from one molecule of fructose-1,5-biphosphate, how?

A

Via two separate reactions:

Reaction 4 and Reaction 5

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22
Q

What is the Net reaction for the energy investment phase of glycolysis?

A

glucose + 2ATP -> 2GAP + 2ADP + 2H+

GAP = glyceraldehyde-3-phosphate

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23
Q

What is important about the moles of GAP produced in phase 1 and the reactions of phase 2?

A

2 moles of GAP = each reaction in phase 2 occurs twice

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24
Q

What happens in Phase 2 of glycolysis (energy payout phase)

A

2 Glyceraldehyde-3-phosphate (GAP) molecules are converted to 2 molecules of pyruvate.

Generates 4 ATP for every 1 glucose

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25
Q

What is the oxidation reaction in the glycolytic pathway?

A

Reaction 6:

Glyceraldehyde-3-phosphate (GAP) + NAD+ + Pi ⇌ 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H+

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26
Q

Reaction 6:

Glyceraldehyde-3-phosphate (GAP) + NAD+ + Pi ⇌ 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H+

  • Type of reaction
  • Reversible?
  • Coupled?
  • Catalyzed by?
A

Reaction 6:

Glyceraldehyde-3-phosphate (GAP) + NAD+ + Pi ⇌ 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H+

  • Type of reaction
    • oxidation
  • Reversible?
    • yes, delta G approx 0
  • Coupled?
    • no, Energy capture step (production of NADH)
  • Catalyzed by?
    • GAPDH (Glyceraldehyde-3-phosphate dehydrogenase)
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27
Q

Why is 1,3-BPG considered high energy?

A

1,3-bisphosphoglycerate is a high energy intermediate because it is an acyl phosphate (phosphate attached to carboxylates)

  • Large phosphate transfer potential
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28
Q

Why does 1,3-BPG have a large phosphate-transfer potential?

A

Large negative delta G of hydrolysis

  • Go from Acyl phosphate (mixed anhydride structure) to produce 2 molecules with more resonance stabilization (there are more resonance structures for Pi and the carboxyl than there are for the ester/PO4)
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29
Q

Reaction 7:

1,3-bisphosphoglycerate to 3-phosphoglycerate

  • Reversible?
  • Coupled?
  • Type of Reaction
A

Reaction 7:

1,3-bisphosphoglycerate (source of phosphate to be added to ADP) +ADP ⇄ 3-phosphoglycerate + ATP

  • Reversible?
    • Yes delta G approx G
  • Coupled?
    • Yes to ATP synthesis
      • Synthesis of phosphoanhydride coupled to cleavage of acyl phosphate structure
  • Type of Reaction
    • Substrate-level phosphorylation
    • Generating nucleotide triphosphate as direct product
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30
Q

At what stage of the glycolytic pathway have we recovered the loss from the energy investment stage?

A

Reaction 7

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31
Q

Reaction 8:

3-phosphoglycerate to 2-phosphoglycerate

  • Type of reaction?
  • Reversible?
A

Reaction 8:

3-phosphoglycerate ⇄ 2-phosphoglycerate

  • Type of reaction?
    • Isomerization
  • Reversible?
    • Yes, delta G approx 0
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32
Q

Reaction 9:

2-phosphoglycerate to phosphoenolpyruvate and water

  • Reaction type?
  • Reversible?
A

Reaction 9:

2-phosphoglycerate ⇄ phosphoenolpyruvate and water

  • Reaction type?
    • Dehydration
  • Reversible?
    • Yes, delta G approx 0
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33
Q

Reaction 10:

Phosphoenolpyruvate (PEP) to Pyruvate

  • Type of Reaction
  • Reversible?
  • Coupled?
  • Catalyzed by?
A

Reaction 10:

Phosphoenolpyruvate (PEP) + ADP + H+ ⇄ Enolpyruvate ⟶ Pyruvate + ATP

  • Type of Reaction
    • Substrate level phosphorylation
  • Reversible?
    • No, irreversible, large negative delta G
  • Coupled?
    • Yes to ATP synthesis at expense of PEP = energy capture
  • Catalyzed by?
    • Pyruvate kinase (regulated)
34
Q

What are the 3 Irreversible reactions in glycolysis and what are their catalysts?

A
  1. Reaction 1: Glucose to Glucose-6-phosphate
    • catalyzed by hexokinase
  2. Reaction 3: Fructose-6-phosphate to Fructose 1,6-bisphosphate
    • Catalyzed by Phosphofructokinase-1 (PFK-1)
    • Rate limiting
  3. Reaction 10: Phosphoenolpyruvate to pyruvate
    • Catalyzed by pyruvate kinase
35
Q

What makes Reaction 10 (PEP to pyruvate) irreversible?

A

Tautomerization of double bond adjacent to the OH group

  • energy of arrangement greatly favours carbonyl formation over enol
    • Enol is intrinsically unstable
36
Q

What is the oxidation reaction of glycolysis?

A

GAP + NAD+ + Pi 1,3-bisphosphoglycerate + NADH + H+

37
Q

What are the 2 substrate level phosphorylation reactions in glycolysis?

A
  1. Reaction 7:
    • 1,3-BPG + ADP 3-phosphoglycerate + ATP
  2. Reaction 10:
    1. PEP + ADP + H+ -> Pyruvate + ATP
38
Q

What are the 3 isomerization reactions of glycolysis

A
  1. Reaction 2 :
    • G6P F6P
  2. Reaction 5
    • Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate (GAP)
  3. Reaction 8
    • 3-phosphoglycerate 2-phosphoglycerate
39
Q

What is the dehydration reaction in glycolysis?

A

Reaction 9

2-phosphoglycerate phosphoenolpyruvate + H2O

40
Q

What are the two phosphate transfer reactions in glycolysis?

A
  1. Reaction 1
    • Glucose + ATP -> Glucose 6-phosphate + ADP + H+
  2. Reaction 3
    • Fructose 6-Phosphate + ATP Fructose1,6-bisphosphate + ADP + H+
41
Q

What is the Lysis reaction of glycolysis?

A

Reaction 4

Fructose 1,6-bisphosphate dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate

42
Q

What four major processes regulate the flow through metabolic pathways in glycolysis?

A
  1. Substate availability
  2. Alteration of enzyme activity (eg allostery/phosphorylation)
  3. Alteration of amount of enzyme (slow compared to allostery or phosphorylation)
  4. Compartmentation
    • transport processes are controlled
43
Q

How is substrate availability regulated?

A

Via Glucose import (transporters) at the plasma membrane

  • more transporters = more import
44
Q

Which of the 4 important enzymes of glycolysis is most regulated? Why?

A

PFK-1 (phosphofructokinase-1) because it catalyzes the rate limiting step

45
Q

Which enzymes are regulated in glycolysis?

A
  1. Hexokinase
  2. Phosphofructokinase-1 (PFK-1)
  3. Pyruvate kinase
46
Q

What is the effect of Glucose-6-phosphate on Hexokinase?

A

Product inhibition

47
Q

What two molecules inhibit Phosphofructokinase-1

A
  • PFK-1 is inhibited by:
    1. Citrate (from fat synthesis)
    2. ATP (based on energy need)
    3. Phosphoenolpyruvate (PEP)
      • Negative feedback
      • Feedback inhibition
      • Neg heteroallosteric effector (inhibitor)

High ATP = we don’t need to produce more ATP

48
Q

What two molecules activate Phosphofructokinase-1?

A

PFK-1 is activated by

  1. AMP (based on energy need)
    • Positive heteroallosteric effector
      • Shift left to increase activity
  2. Fructose 2,6-bisphosphate
    • hormonal regulation
      • response to insulin
49
Q

What is a inhibitor of pyruvate kinase?

A

ATP

50
Q

What is the activator of Pyruvate kinase?

A

Fructose 1,6-bisphosphate

51
Q

What does an elevated concentration of PEP (Phosphoenolpyruvate) indicate about glycolysis?

A

Elevated PEP signal that the products of glycolysis are not being consumed

52
Q

How is pyruvate kinase regulated?

A
  • Pyruvate kinase is an allosteric enzyme
  • Inhibited by ATP
    • Product inhibition
      • allosteric inhibitor
  • Activated by Fructose-1,6-bisphosphate (yeast)
    • Feedforward activation
53
Q

When pyruvate kinase is inhibited, gluconeogenesis is _____ and glycolysis is ______.

= what type of regulation?

A

When pyruvate kinase is inhibited, gluconeogenesis is active and glycolysis is inhibited.

= what type of regulation?

  • Reciprocal regulation
54
Q

Which two enzymes in the glycolytic pathway are inhibited by ATP?

A

PFK-1 (Phosphofructokinase -1) and PK (Pyruvate kinase)

  • Synchronous regulation of irreversible reactions
55
Q

What are the ATP investment reactions of glycolysis?

A

Reaction 1: glucose + ATP -> glucose-6-phosphate + ADP + H+

and

Reaction 3: F-6-P + ATP -> fructose-1,6-bisphosphate + ADP + H+

56
Q

Glucose is synthesized from ________ in an ________ process

A

Glucose is synthesized from glucose-6-phosphate in an anabolic process

  • No ATP is used to generate G6P from glycogen
  • Increases NET yield of ATP (1 more per unit)
57
Q

Why is an anaerobic fate for pyruvate required?

A

To regenerate NAD+ for the oxidation reaction in glycolysis under anaerobic conditions

  • Under anaerobic conditions there is no e- transport chain (ETC) to convert NADH to NAD+ at complex 1
  • Need a way to convert NADH -> NAD+
    • GAPDH rxn won’t happen without NAD+ available to convert glyceraldehyde 3 phosphate to 1,3-bisphosphoglycerate
58
Q

What are the 3 Catabolic Fates of Pyruvate?

A
  1. Production of ethanol under anaerobic conditions (in Yeast)
  2. Production of lactate under aerobic conditions (in RBC - no Mito = always aerobic)
  3. Form Alanine
    • reverse (deamination) to form pyruvate from alanine
59
Q

How might lactate transport be beneficial to an athlete?

A

Symport (lactate + proton) out of muscle => decrease pH in bloodstream => Bohr Effect => increased O2 release from Hb (hemoglobin)

60
Q

What causes acidotic damage to muscle fibres?

A

Hydrolysis of ATP by myosin during vigorous muscle contraction

  • Not from LACTATE
61
Q

Where is lactate used and how?

A

Cardiac tissue

  • Under aerobic conditions Lactate is converted to pyruvate and then to Acetyl-CoA + CO2
62
Q

What are the two steps in the production of ethanol from pyruvate?

A
  1. Decarboxylation (of pyruvate)
  2. Reduction
  • Pyruvate -> Acetaldehyde -> Ethanol
63
Q

Pyruvate to Acetyl CoA occurs under ______ conditions?

A

Pyruvate to Acetyl CoA occurs under aerobic conditions?

64
Q

The Pyruvate dehydrogenase reaction is:

  • Catalyzed by ___________
  • Links which two cycles?
  • Where does pyruvate dehydrogenase (PDH) occur?
A

The Pyruvate dehydrogenase reaction is:

  • Catalyzed by pyruvate dehydrogenase complex
  • Links which two cycles?
    • Links Glycolysis to Citric Acid Cycle (CAC)
  • Where does pyruvate dehydrogenase (PDH) occur?
    • Matrix of the mitochondria
65
Q

Four processes that occur in the matrix of the mitochondria

A
  1. Pyruvate dehydrogenase
  2. Citric Acid Cycle
  3. Oxidative phosphorylation
  4. Beta-oxidation (fatty acids) (aerobic/catabolic)
66
Q

Pyruvate must pass _______ to get to the _______ of the mitochondria

A

Pyruvate must pass 2 membranes to get to the matrix of the mitochondria

67
Q

How does pyruvate get from the cytosol to the matrix?

A
  • Cytosol to intermembrane space via Porins
    • ​allows free diffusion across the outer mitochondrial membrane
  • Intermembrane space to matrix via Pyruvate Translocase
    • ​Symporter (Pyruvate and H+)
    • Across inner mito membrane
68
Q

Pyruvate is converted to acetyl-CoA via the __________

A

Pyruvate is converted to acetyl-CoA via the Pyruvate dehydrogenase Complex (PDC or PDH)

69
Q

What makes Acetyl CoA high energy?

A

Acetyl CoA is a thioester = high energy

70
Q

What is the structure of Acetyl-CoA?

A
  • Thiol converted to thioester
    • Acetyl group attached via thioester bond
    • The Thiol group (HS) is all we care about
  • Derivative of Vit B5 linked to an Adenosine Nucleotide (AMP)
  • Functional portion is the terminal sulfhydryl group (thiool) which forms a thioester bond with acetyl groups
71
Q

The formation of acetyl-CoA is a key _______ step in ________ metabolism

A

The formation of acetyl-CoA is a key irreversible step in Carbohydrate metabolism

72
Q

The Pyruvate Dehydrogenase Reaction:

Pyruvate + CoA + NAD+ -> Acetyl-CoA + NADH + CO2

  • Type of reaction?
  • Reversible?
  • Catalyst?
A

The Pyruvate Dehydrogenase Reaction:

Pyruvate + CoA + NAD+ -> Acetyl-CoA + NADH + CO2

  • Type of reaction?
    • Oxidative decarboxylation
    • Transacetylation (transfer of CoA)
  • Reversible?
    • No - Irreversible
  • Catalyst?
    • Pyruvate Dehydrogenase Comples (PDH)
  • Requires 5 cofactors including:
    1. NAD+
    2. FAD (prosthetic group in PDH)
    3. CoA
73
Q

Pyruvate Dehydrogenase Complex is a ______ complex that contains multiple copies of _________ and 5 cofactors including _____, _____ and ______

A

Pyruvate Dehydrogenase Complex is a multienzyme complex that contains multiple copies of three catalytic enzymes and 5 cofactors including NAD+, FAD (prosthetic group) and CoA

Decarboxylate

74
Q

Pyruvate Dehydrogenase Complex (PDH) is regulated by:

A
  1. Kinases (phosphorylation)
  2. Phosphatases (dephosphorylation)
  3. Energy (ATP) requirements
    • NAD+/NADH ratio
    • Ca++ concentration
    • Acetyl-CoA
75
Q

What are three advantages of multienzyme complexes?

A
  1. Speeds up reaction time
  2. Limits number of side reactions
  3. Enzymes controlled as a single unit (concerted regulation)
76
Q

Can acetyl-CoA be used to make glucose in mammals?

A

NO - it is irreversible

77
Q

What effect does NADH have on Pyruvate dehydrogenase complex (PDH)?

A

NADH inhibits (regulates) PDH

  • Allostery
  • Protein kinase activation (phosphorylation of PDH)
78
Q

What is the effect of Acetyl-CoA on Pyruvate Dehydrogenase Complex (PDH)

A

Acetyl-CoA is an inhibitor of PDH

  • activates protein kinase (phosphorylation of PDH)
79
Q

What effect does Ca++ have on PDH?

A

Ca++ activates protein phosphatase -> activation of PDH = dephosphorylation of PDH

80
Q

How is PDH turned on and off?

A

via reversible phosphorylation:

  • Phosphorylation (via kinase) switches off the activity of the complex
    • NADH and Acetyl-CoA activate kinase
  • Dephosphorylation (via phosphatase) activates PDH
    • Ca++ activates phosphatase
81
Q

How is pyruvate dehydrogenase (PDH) regulated by substrate availability?

A

Increase reaction rate when more substrate is available:

  • Inhibition of the complex:
    • NADH and Acetyl-CoA
  • Activation of complex:
    • NAD+ and HS-CoA

BIOCH 200 (9 decks)

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