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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
What is the oxidation reaction in the glycolytic pathway?
Reaction 6: Glyceraldehyde-3-phosphate (GAP) + NAD+ + Pi ⇌ 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H+
26
Reaction 6: Glyceraldehyde-3-phosphate (GAP) + NAD+ + Pi ⇌ 1,3-bisphosphoglycerate (1,3-BPG) + NADH + H+ * Type of reaction * Reversible? * Coupled? * Catalyzed by?
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)**
27
Why is 1,3-BPG considered high energy?
1,3-bisphosphoglycerate is a high energy intermediate because it is an acyl phosphate (phosphate attached to carboxylates) * Large phosphate transfer potential
28
Why does 1,3-BPG have a large phosphate-transfer potential?
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)
29
Reaction 7: 1,3-bisphosphoglycerate to 3-phosphoglycerate * Reversible? * Coupled? * Type of Reaction
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
30
At what stage of the glycolytic pathway have we recovered the loss from the energy investment stage?
Reaction 7
31
Reaction 8: 3-phosphoglycerate to 2-phosphoglycerate * Type of reaction? * Reversible?
Reaction 8: 3-phosphoglycerate ⇄ 2-phosphoglycerate * Type of reaction? * **Isomerization** * Reversible? * **Yes, delta G approx 0**
32
Reaction 9: 2-phosphoglycerate to phosphoenolpyruvate and water * Reaction type? * Reversible?
Reaction 9: 2-phosphoglycerate ⇄ phosphoenolpyruvate and water * Reaction type? * **Dehydration** * Reversible? * **Yes, delta G approx 0**
33
Reaction 10: Phosphoenolpyruvate (PEP) to Pyruvate * Type of Reaction * Reversible? * Coupled? * Catalyzed by?
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
What are the 3 Irreversible reactions in glycolysis and what are their catalysts?
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
What makes Reaction 10 (PEP to pyruvate) irreversible?
Tautomerization of double bond adjacent to the OH group * energy of arrangement greatly favours carbonyl formation over enol * Enol is intrinsically unstable
36
What is the oxidation reaction of glycolysis?
GAP + NAD+ + Pi 1,3-bisphosphoglycerate + NADH + H+
37
What are the 2 substrate level phosphorylation reactions in glycolysis?
1. Reaction 7: * 1,3-BPG + ADP 3-phosphoglycerate + ATP 2. Reaction 10: 1. PEP + ADP + H+ -\> Pyruvate + ATP
38
What are the 3 isomerization reactions of glycolysis
1. Reaction _2_ : * G6P F6P 2. Reaction _5_ * Dihydroxyacetone phosphate Glyceraldehyde-3-phosphate (GAP) 3. Reaction _8_ * 3-phosphoglycerate 2-phosphoglycerate
39
What is the dehydration reaction in glycolysis?
Reaction 9 2-phosphoglycerate phosphoenolpyruvate + H2O
40
What are the two phosphate transfer reactions in glycolysis?
1. Reaction 1 * Glucose + ATP -\> Glucose 6-phosphate + ADP + H+ 2. Reaction 3 * Fructose 6-Phosphate + ATP Fructose1,6-bisphosphate + ADP + H+
41
What is the Lysis reaction of glycolysis?
Reaction 4 Fructose 1,6-bisphosphate dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate
42
What four major processes regulate the flow through metabolic pathways in glycolysis?
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
How is substrate availability regulated?
Via Glucose import (transporters) at the plasma membrane * more transporters = more import
44
Which of the 4 important enzymes of glycolysis is most regulated? Why?
PFK-1 (phosphofructokinase-1) because it catalyzes the rate limiting step
45
Which enzymes are regulated in glycolysis?
1. Hexokinase 2. Phosphofructokinase-1 (PFK-1) 3. Pyruvate kinase
46
What is the effect of Glucose-6-phosphate on Hexokinase?
**Product inhibition**
47
What two molecules inhibit Phosphofructokinase-1
* 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
What two molecules activate Phosphofructokinase-1?
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
What is a inhibitor of pyruvate kinase?
ATP
50
What is the activator of Pyruvate kinase?
Fructose 1,6-bisphosphate
51
What does an elevated concentration of PEP (Phosphoenolpyruvate) indicate about glycolysis?
Elevated PEP signal that the products of glycolysis are not being consumed
52
How is pyruvate kinase regulated?
* Pyruvate kinase is an allosteric enzyme * Inhibited by ATP * Product inhibition * allosteric inhibitor * Activated by Fructose-1,6-bisphosphate (yeast) * Feedforward activation
53
When pyruvate kinase is inhibited, gluconeogenesis is _____ and glycolysis is \_\_\_\_\_\_. = what type of regulation?
When pyruvate kinase is inhibited, gluconeogenesis is _active_ and glycolysis is _inhibited_. = what type of regulation? * **Reciprocal regulation**
54
Which two enzymes in the glycolytic pathway are inhibited by ATP?
PFK-1 (Phosphofructokinase -1) and PK (Pyruvate kinase) * Synchronous regulation of irreversible reactions
55
What are the ATP investment reactions of glycolysis?
Reaction 1: glucose + ATP -\> glucose-6-phosphate + ADP + H+ and Reaction 3: F-6-P + ATP -\> fructose-1,6-bisphosphate + ADP + H+
56
Glucose is synthesized from ________ in an ________ process
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
Why is an anaerobic fate for pyruvate required?
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
What are the 3 Catabolic Fates of Pyruvate?
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
How might lactate transport be beneficial to an athlete?
Symport (lactate + proton) out of muscle =\> decrease pH in bloodstream =\> Bohr Effect =\> increased O2 release from Hb (hemoglobin)
60
What causes acidotic damage to muscle fibres?
Hydrolysis of ATP by myosin during vigorous muscle contraction - Not from LACTATE
61
Where is lactate used and how?
Cardiac tissue * Under aerobic conditions Lactate is converted to pyruvate and then to Acetyl-CoA + CO2
62
What are the two steps in the production of ethanol from pyruvate?
1. Decarboxylation (of pyruvate) 2. Reduction * Pyruvate -\> Acetaldehyde -\> Ethanol
63
Pyruvate to Acetyl CoA occurs under ______ conditions?
Pyruvate to Acetyl CoA occurs under _aerobic_ conditions?
64
The Pyruvate dehydrogenase reaction is: * Catalyzed by \_\_\_\_\_\_\_\_\_\_\_ * Links which two cycles? * Where does pyruvate dehydrogenase (PDH) occur?
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
Four processes that occur in the matrix of the mitochondria
1. Pyruvate dehydrogenase 2. Citric Acid Cycle 3. Oxidative phosphorylation 4. Beta-oxidation (fatty acids) (aerobic/catabolic)
66
Pyruvate must pass _______ to get to the _______ of the mitochondria
Pyruvate must pass _2 membranes_ to get to the _matrix_ of the mitochondria
67
How does pyruvate get from the cytosol to the matrix?
* 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
Pyruvate is converted to acetyl-CoA via the \_\_\_\_\_\_\_\_\_\_
Pyruvate is converted to acetyl-CoA via the _Pyruvate dehydrogenase Complex (PDC or PDH)_
69
What makes Acetyl CoA high energy?
Acetyl CoA is a thioester = high energy
70
What is the structure of Acetyl-CoA?
* 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
The formation of acetyl-CoA is a key _______ step in ________ metabolism
The formation of acetyl-CoA is a key _irreversible_ step in _Carbohydrate_ metabolism
72
The Pyruvate Dehydrogenase Reaction: Pyruvate + CoA + NAD+ -\> Acetyl-CoA + NADH + CO2 * Type of reaction? * Reversible? * Catalyst?
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
Pyruvate Dehydrogenase Complex is a ______ complex that contains multiple copies of _________ and 5 cofactors including \_\_\_\_\_, _____ and \_\_\_\_\_\_
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
Pyruvate Dehydrogenase Complex (PDH) is regulated by:
1. Kinases (phosphorylation) 2. Phosphatases (dephosphorylation) 3. Energy (ATP) requirements * NAD+/NADH ratio * Ca++ concentration * Acetyl-CoA
75
What are three advantages of multienzyme complexes?
1. Speeds up reaction time 2. Limits number of side reactions 3. Enzymes controlled as a single unit (concerted regulation)
76
Can acetyl-CoA be used to make glucose in mammals?
NO - it is irreversible
77
What effect does NADH have on Pyruvate dehydrogenase complex (PDH)?
NADH inhibits (regulates) PDH * Allostery * Protein kinase activation (phosphorylation of PDH)
78
What is the effect of Acetyl-CoA on Pyruvate Dehydrogenase Complex (PDH)
Acetyl-CoA is an inhibitor of PDH * activates protein kinase (phosphorylation of PDH)
79
What effect does Ca++ have on PDH?
Ca++ activates protein phosphatase -\> activation of PDH = dephosphorylation of PDH
80
How is PDH turned on and off?
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
How is pyruvate dehydrogenase (PDH) regulated by substrate availability?
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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