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BIOC192 2024 > Lecture 24 - Glucose as a fuel molecule #2 > Flashcards

Lecture 24 - Glucose as a fuel molecule #2 Flashcards

1
Q

What are the basic steps of Glycolysis?

A
  1. Splitting of glucose (one 6 Carbon glucose to two 3 Carbon pyruvate molecules)
  2. Energy is conserved in ATP and NADH
  3. Pyruvate may be further metabolised aerobically or anaerobically
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2
Q

What is the activation of glucose?

A

Getting the molecule into a form so energy can be captured - this requires an energy input

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3
Q

What are the two phases of glycolysis?

A
  1. Energy Investment phase
  2. Energy Payoff phase
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4
Q

What happens during the energy investment phase?

A

Energy is used/invested in making the glucose molecule ready for splitting

The molecule is split (1X6C to 2X3C) at the end of the investment phase

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5
Q

What two molecules are glucose split into during the energy investment phase?

A

Pyruvate

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6
Q

How many ATP are spent during the energy investment phase?

A

2 ATP

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7
Q

What happens during the energy payoff phase?

A

4 ADP turns into 4 ATP

2 NAD+ turns into 2 NADH

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8
Q

What is the first key reaction for the activation of glucose?

A

Glucose + phosphate ➔ glucose-6-phosphate + H2O

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9
Q

What enzyme adds a phosphate onto glucose

A

Hexokinase

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10
Q

Is the first key reaction for the activation of glucose energetically favourable?

A

No, has +ve ΔG, but is required for glucose to be used as a fuel molecule

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11
Q

How is this non-spontaneous first key reaction for the activation of glucose carried out?

A

By the coupling of the reaction (+ΔG) to ATP hydrolysis(-ΔG). Allowing the overall reaction to be spontaneous (-ΔG)

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12
Q

What is the overall coupled reaction?

A

Glucose + ATP ➔ glucose-6-phosphate + ADP

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13
Q

What is the second key reaction in the activation of glucose?

A

Glucosephosphate isomerase - rearrangement from glucose-6-phosphate into fructose-6-phosphate (F-6-P) (+ΔG)

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14
Q

What is the third key reaction in activation of glucose?

A

Phosphofructokinase - 2nd activation of glucose that uses ATP hydrolysis to convert Fructose-6-phosphate into Fructose-1,6-biphosphate (FBP)

(addition of second phosphate)

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15
Q

What occurs during the splitting (aldolase) reaction?

A

Occurs after the third key step of glucose activation.

FBP is split by aldolase forming DHAP, and G-3-P

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16
Q

What phase of glycolysis is G-3-P used?

A

In the energy payoff phase

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17
Q

What is the consequence of G-3-P being used up in the energy payoff phase?

A

The G-3-P concentration is low which drives the reaction from DHAP to G-3-P

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18
Q

What enzyme catalyses the rearrangement of DHAP into G-3-P?

A

Triose phosphate isomerase

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19
Q

What is substrate level phosphorylation? (SLP)

A

The direct use of energy from a substrate molecule to drive the synthesis of ATP (or equivalent)

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20
Q

What is one way to release energy to drive a SLP?

A

By the cleavage of a high-energy phosphate ester bond on a substrate

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21
Q

What is NAD?

A

A coenzyme required by some enzymes that catalyse redox reactions

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22
Q

What is NAD derived from ?

A

Niacin (vitamin B3)

23
Q

What are the two forms of NAD?

A

NAD+(the oxidised form)
NADH(the reduced form)

24
Q

What is the importance of oxidising G-3-P?

A

It is a reaction for making an ATP profit

25
Q

How does oxidising G-3-P help make ATP profit?

A

it powers the addition of a phosphate to itself forming 1,3-BPG

26
Q

Does the addition of a phosphate require ATP?

A

No, phosphate from solution added to substrate

27
Q

What is reduced as G-3-P is oxidised?

A

NAD+

28
Q

Which carbon on 1,3-BPG is very reactive?

A

The first one

29
Q

What is 1,3-BPG converted into?

A

3PG

30
Q

What does occurs during the reaction from 1,3-BPG to 3PG?

A

Phosphate is cleaved from the 3-BPG by phosphoglycerate kinase this releases energy which is coupled with substrate level phosphorylation producing some ATP

31
Q

How does arsenic poison glycolysis?

A

Binds to the phosphoglycerate and formed 1-Arseno-3-phosphoglycerate instead of 1,3-BPG. So no ATP is synthesised by the phosphoglycerate kinase.

32
Q

What then happens to 3PG?

A

Rearranged to make 2PG, and then 2PG is rearranged to make PEP. This puts the molecule in a form that enables the next reactions

33
Q

What happens to PEP?

A

A phosphate is cleaved off of it by Pyruvate kinase, releasing energy which is coupled to the second substrate level phosphorylation in order to produce ATP

34
Q

How is the overall change in Gibbs free energy throughout glycolysis?

A

Negative so pathway is energetically favourable (some energy is converted into heat)

35
Q

What happens in the citric acid cycle?

A

Aerobic oxidation - Pyruvate is converted to acetyl-CoA to be further metabolized
in the citric acid cycle

36
Q

What is Coenzyme A (CoA) derived from?

A

pantothenic acid (vitamin B5)

37
Q

Is CoA a carrier of electrons?

A

No (not reduced/oxidized)

38
Q

What does CoA carry?

A

Acyl groups - (2 C to long chains)

39
Q

What are the two forms of CoA

A

free coenzyme A: CoASH
acyl group attached: Acyl-CoA (AcCoA)

40
Q

Where does the aerobic oxidation of pyruvate occur?

A

In the mitochondrial matrix.

41
Q

What enzyme complex is involved in the aerobic oxidation of pyruvate?

A

Pyruvate dehydrogenase complex.

42
Q

What type of reaction is the conversion of pyruvate to Acetyl-CoA?

A

Oxidative decarboxylation.

43
Q

What molecule is released during the decarboxylation of pyruvate?

A

CO₂ (carbon dioxide).

44
Q

What is added to the two-carbon chain after pyruvate is oxidized?

A

Coenzyme A (CoA).

45
Q

What happens to pyruvate in the pyruvate dehydrogenase reaction?

A

Pyruvate is oxidized, releasing energy that is captured in NADH.

46
Q

Which cofactors or coenzymes are involved in the pyruvate dehydrogenase reaction?

A

TPP (thiamine pyrophosphate), FAD, lipoic acid, NAD⁺, and Mg²⁺.

47
Q

What is the overall change in free energy (ΔG°’) for the conversion of pyruvate to Acetyl-CoA?

A

ΔG°’ = -33 kJ/mol.

48
Q

What happens during anaerobic glycolysis?

A

Instead of entering the citric acid cycle, pyruvate becomes lactate from the enzyme lactate dehydrogenase

49
Q

What does lactate do?

A

Causes muscle fatigue

50
Q

What happens to the energy captured in NADH during the lactate dehydrogenase reaction?

A

The energy is lost

51
Q

How is the concentration of coenzymes in cells?

A

Low

52
Q

When are coenzymes oxidised during aerobic oxidation?

A

In oxidative phosphorylation

53
Q

What does lactate formation allow?

A

Lactate formation allows for the regeneration of NAD+ as lactate dehydrogenase
reaction oxidizes NAD meaning that there is enough NAD for the G-3-P dehydrogenase reaction

BIOC192 2024 (35 decks)

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