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Biology - Macromolecules > Glycolysis Steps > Flashcards

Glycolysis Steps Flashcards

1
Q

What are the sources of glucose?

A

Dietary glycogen/starch breakdown OR gluconeogenesis

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2
Q

Where are the glycolytic enzymes found?

A

Cytosol.

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3
Q

Glycolysis

A

Conversion of glucose to two C3 pyruvate units, where free energy released is harrvested to synthesise ATP from ADP and Pi.

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4
Q

What is the first stage of glycolysis?

A

Energy investment stage, where hexose glucose is phosphorylated and cleaved, yielding two glyceraldehyde-3phosphate, consuming 2 ATP.

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5
Q

What is the second stage of glycolysis?

A

Energy Recovery, where the two GAH3P are converted to pyruvate with generation of 4 ATP, a net profit of 2 ATP per glucose.

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6
Q

What is the importance of the energy investment stage?

A

Pi transfer from ATP to hexose does not immediately result in high energy compounds, these result from the proceeding enzymatic reactions, converting low energy compounds to high phospohate group transfer potential capable of ADP phosphorylation.

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7
Q

Glycolytic Reaction Pathway

A

Glucose + 2 NAD+ + 2 ADP + Pi —> 2 Pyruvate + 2 NADH + 2 ATP + 2 H20 + 4H+

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8
Q

What requirements does glycolysis have due to its NAD dependence?

A

The 2 NADH formed from glycolysis must be reoxidesed, to keep pathway supplied with NAD+

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9
Q

1) Hexokinase

A

Transfers ATP phosphate group from ATP to glucose forming G6P.

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10
Q

What is the structure of Glucose?

A

Cyclical hexagon sturcture with hydroxyl groups + H at all but C5, with an O between C1 and C5, with C6 having two hydrogen.

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11
Q

What is a characteristic of hexokinase, in terms of its ability to phosphorylate?

A

It is ubiquitous, catalysing phosphorylation of mannose, fructose AND glucose(not galactose)

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12
Q

1) What is Hexokinase dependent on?

A

Magnesium

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13
Q

1) Why is hexokinase dependent on magnesium?

A

Shielding of - charge of ATP phosphates O atoms, so the phosphorous atom is more accessible for nucleophilic attack.

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14
Q

1) What part of glucose attacks ATP?

A

C6 hydoxyl group.

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15
Q

2) Phosphoglucose Isomerase

A

Converts G6P to F6P in isomerisation.

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16
Q

2) What forms do G6P and F6P exist in and why is this significant?

A

Cyclical forms, thus reaciton requires opening of rings for isomerisation.

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17
Q

2) Structural change of F6P

A

C1-C5 oxygen bond changes to C2-C5

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18
Q

2) What are the 5 steps of Phosphoglucose Isomerase?

A

Substrate binds
Enzymatic acid catalyses ring opening
Enzymatic base abstrats proton from C2, forming the cis-enediolate intermediate
Proton is replaced on C1
Ring close, forming product.

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19
Q

3) Phosphofructokinase

A

This phosphorylates F6P into F-1,6 Biphosphate.

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20
Q

What makes something a biphosphate opposed to a diphosphate?

A

The phosphates are not directly attached to one another.

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21
Q

3) Reactive steps of phosphofructokinase

A

Nucleophilic attack by the C1 hydroxyl of F6P on the electrophilic phosphorous atom of the Mg-ATP, with transfer of the phosphate group to C1.

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22
Q

4) Aldolase

A

Aldolase cleaves F-1,6 BP into GA3P and DHAP.

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23
Q

4) What are the structural changes of F-1,6 BP to GA3P and DHAP?

A

C1, C2 and C3 becoming DHAP whilst C4, C5 and C6 becoming GAH3P.

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24
Q

4) What are the steps of Aldolase?

A

Substrate binds
F-1,6BP carbonyl reacts with amino group of active site, forming a protonate schiff base.
C3-C4 bond cleavage results in GAP release and enamine formation.
Enamine is protonated to same schiff base
This is hydrolysed releasing DHAP

25
Q

5) Triose Phopshate Isomerase

A

This interconverts DHAP into GAP through an enediol intermediate

26
Q

Schiff Base

A

Imine bonds formed by nucleophilic attack of amine to aldehyde groups.

27
Q

Enamine

A

An unsaturtaed compound derived from a ketone/aldehyde reaction, with an amine, with H2O loss.

28
Q

Imine

A

Compounds containing a carbon-nitrogen double bond.

29
Q

What steps of stage 1 are ATP consumed in?

A

Hexokinase and Phosphofructokinase.

30
Q

What is the state of glycolysis at the end of stage 1, step 5?

A

1 glucose transformed into two GAP, with low energy bonds.

31
Q

6) Glyceraldehyde-3 Phosphate Dehydrogenase

A

This phosphorylase GAH3P using NAD+ and Pi.

32
Q

Acyl Group

A

A double bonded oxygen atom and a alkyl group

33
Q

Alkyl Group

A

A group derived from an alkane by loss of a hydrogen.

34
Q

6) Importance of GAH3PD reaction?

A

Its aldehyde oxidation is exergonic, driving synthesis of the high energy acyl-phosphate; 1,3 BPG.

35
Q

6) Structure of GAH3P

A

C1 a carbonyl and H, C2 a H and Hydroxyl and C3 with 2 H and phosphate group.

36
Q

6) Steps in GAH3PD pathway.

A

GAP binds enzyme
Nucleophilic Sulfhydryl group attacks aldehyde forming thiohemiacetal.
Thiohemiacetal is oxidised to acyl thioester
Po binds enzyme-thioester-NADH complex
Thioester intermediate undergoes nucleophilic attack by Pi, forming 1,3 - BPG.

37
Q

6) How is thiohemiacetal oxidised to an acyl thioester?

A

Direct hydride transfer to NAD+ which has high free energy of hydrolysis.

38
Q

6) What is the importance of the Hydride transfer to NAD+ when thiohemiacetal is oxidised?

A

It conserves energy of aldehyde oxidation, opposed to dissipating.

39
Q

7) Phosphoglycerate Kinase

A

1,3 - BPG is converted to 3PG.

40
Q

How can an unfavourable reaction forward two reactions?

A

Couping with a highly favourable reaction.

41
Q

How does step 7 relate to step 6 in terms of reaction coupling?

A

GAPDH is endergonic, yet transfer of phosphate group from 1,3 BPG to ADP is exergonic, so NADH and ATP synthesis from GAP, Pi, NAD+ and ADP is favourable.

42
Q

6) DeltaG of GAH3PD?

A

+ 6.7 kJ

43
Q

7) DeltaG of Phosphoglycerate Kinase?

A

-18.8 kJ

44
Q

What is the net DeltaG of step 6 and 7 coupling?

A

-12.1 kJ

45
Q

8) Phosphoglycerate Mutase

A

This converts 3PG into 2PG as an energetically neutral reaction.

46
Q

8) Steps of Phosphoglycerate Mutase?

A

3PG binds
Enzyme phosphorylates substrate at C2
Substrate C3 phosphorylates enzymes

47
Q

8) What is a significant structural component of phosphoglycerate mutase?

A

Its active site contains a phosphate group that transfers to substrate.

48
Q

8) What are the consequences of the ability of the 2,3 BPG intermediate leaving the active site?

A

Cytosol must have trace amounts of 2,3 BPG at all times to regenerate the active enzyme.

49
Q

9) Enolase

A

This dehydrates 2PG to phosphoenolpyruvate

50
Q

10) Pyruvate Kinase

A

This couples free energy of PEP cleavage to ATP synthesis, with formation of ATP.

51
Q

10) Steps of Pyruvate Kinase?

A

ADP phosphoryl oxygen nucleophilically attacks PEP phosphate atom, displacing enolpyruvate, forming ATP.
Enolpyruvate tautomerises to pyruvate.

52
Q

Tuatomerism

A

Where a chemical compound exists in two or more interconvertible states, different only in the positon of an atomic nulcues, like hydrogen.

53
Q

10) What does 2PG dehydration result in?

A

Formation of a high energy compound capable of ATP synthesis.

54
Q

9) DeltaG of 2PG hydrolysis?

A

-16kJ, insufficent to drive ATP synthesis.

55
Q

What are the three products of Glycolysis?

A

Net yield of 2 ATP, two NADH and two pyruvate.

56
Q

What is the function of NADH during glycolysis?

A

As a store/source of free eenrgy, recovered by its oxidation to NAD+

57
Q

How is NADH used in ETC?

A

Its stored free energy synthesises ATP from ADP with regeneration of oxidised NAD+

58
Q

What happens to Pyruvate in Aerobic Glycolysis?

A

Complete pyruvate carbon oxidation to CO2 mediated by CAC, enerrgy released driving ATP synthesis.

59
Q

What happens to Pyruvate in Anaerobic conditions?

A

It is metabolised to a lesser extent to regenerate NAD+

Biology - Macromolecules (16 decks)

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