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BIOC192 > Lecture 28: GLUCOSE AS A FUEL MOLECULE - GLYCOLYSIS > Flashcards

Lecture 28: GLUCOSE AS A FUEL MOLECULE - GLYCOLYSIS Flashcards

1
Q

What happens to glucose in glycolysis?

A

It is oxidised

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2
Q

Where is glucose found?

A

In all organisms (animals, fungi, plants and bacteria)

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3
Q

Where is glycolysis usually in eukaryotes?

A

Usually cytoplasmic (other pathways are in the mitochondria)

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4
Q

What cells can use glucose?

A

All cells can use glucose but some rely on/preferentially use it

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5
Q

What is glucose an essential fuel for?

A

Red blood cells because they don’t have mitochondria and so lack the other pathways

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6
Q

Where is glucose the favoured fuel?

A

In the brain and eyes

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7
Q

What is the energy requirement of the brain?

A

High - human brain requires around 120g of glucose per day

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8
Q

Do brain cells have mitochondria?

A

Yes

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9
Q

What are the theories as to why glucose is the favoured fuel in the brain?

A

Supply and safety

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10
Q

What is involved in the supply theory?

A

Glucose easily crosses the blood-brain barrier (through thick blood vessels) but fats do not

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11
Q

What is involved in the safety theory?

A

A high level of fatty acid metabolism is dangerous. Relying on mitochondria risks anoxia (low oxygen) and production of reactive oxygen species (damaging)

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12
Q

Why is glucose favoured in the eye?

A

Because blood vessels (bringing oxygen) and mitochondria would refract light in the optical path (lens, cornea) to retina interfering with our vision

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13
Q

What do white muscle cells use?

A

Glucose (sprinting)

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14
Q

What do red muscle cells use?

A

Fats (endurance)

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15
Q

What happens in glycolysis?

A

Glucose (6C) is split to form 2 pyruvate (3C) to conserve/extract energy in ATP and NADH. Pyruvate may be further metabolised

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16
Q

What are the two phases of glycolysis?

A

Energy investment and energy payoff

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17
Q

What happens in the energy investment phase?

A

Activation of glucose - getting the molecule into a form so that energy can be captured. Uses 2xATP

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18
Q

What happens in the energy payoff phase?

A

Make 4ATP and 2NADH

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19
Q

When does the splitting of the molecules occur?

A

At the end of the investment phase

20
Q

What is formed from splitting the molecule?

A

2 different 3C molecules. After a conversion, both are processed in the same way

21
Q

What is the reaction of glucose to glucose-6-phosphate (G-6-P)?

A

The first activation of glucose which is coupled to ATP hydrolysis (delta G = -16kJ/mol)

22
Q

What is the reaction of glucose-6-phosphate (G-6-P) to fructose-6-phosphate (F-6-P)?

A

A rearrangement (delta G = +1.6kJ/mol). It is driven froward in the reaction because the reactant (G-6-P) is constantly being formed and the product (F-6-P) is constantly being used

23
Q

What is the reaction of fructose-6-phosphate to fructose-1,6-biphosphate (FBP)?

A

2nd activation of glucose by adding a phosphate coupled to ATP hydrolysis (delta G = -14kJ/mol)

24
Q

What is the reaction of FBP to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate (G-3-P)?

A

The splitting/aldolase reaction. 1x 6C, 2P to 2x 3C, 1P

25
Q

What does triosephosphate isomerase do?

A

Converts between the two products of splitting. G-3-P is used in the pathway

26
Q

What are the pathways for ATP synthesis?

A

Substrate level phosphorylation and oxidative phosphorylation

27
Q

What happens in substrate level phosphorylation?

A

Direct (A+ADP&raquo_space; B+ATP). Energy comes from the substrate

28
Q

What happens in oxidative phosphorylation?

A

Indirect (reduced coenzymes)

29
Q

What is one way to release the energy to drive a substrate level phosphorylation?

A

To cleave high energy phosphoanhydride bond on the substrate but we add a phosphate in the activation so what is the gain?

30
Q

What is a key reaction for making an ATP profit?

A

Oxidation of glyceraldehyde-3-phosphate to 1,3-biphosphoglycerate. NAD+ is reduced and provides the oxidising power and so the addition of the phosphate powered by the oxidation of G-3-P does not require ATP

31
Q

What is in the first substrate level phosphorylation?

A

The #1 carbon phosphate of 1,3-BPG is very reactive and so removal of the phosphate by phosphoglycerate kinase releases energy (delta G = 49.3 kJ/mol) that is used fro substrate level phosphorylation (ADP +PI >ATP = +30 kJ/mol, overall = -19.3 kJ.mol). It is the phosphate from the substrate used to make ATP

32
Q

What does arsenic do to glycolysis?

A

it poisons it as arsenate substitutes for phosphate. G-3-P >1-Arseno-3-phosphoglycerate>3PG

33
Q

What does arsenate do?

A

It is unstable and so hydrolyses spontaneously by energy which is not captured. ATP is not synthesised by phosphoglycerate kinase and there is no net gain of energy in glycolysis

34
Q

What are the steps after the first substrate level phosphorylation?

A

Rearrangements to get the molecule into a form that enables the following reactions

35
Q

What happens in the second substrate level phosphorylation?

A

removal of phosphate from PEP to make pyruvate releases energy (delta G = -61.9 kJ/mol) that is used in substrate level phosphorylation (ADP + P1 > ATP, delta G=+30 kJ/mol). Overall delta g = -31.9 kJ/mol. The phosphate is used to make ATP

36
Q

What is the overall formula for glycolysis?

A

Glucose + 2NAD+ + 2ADP + 2Pi&raquo_space; 2 pyruvate + 2NADH + 2ATP + 2H+

37
Q

What is the overall delta G for glycolysis?

A

-73.3 kJ/mol so the pathway is energetically favourable

38
Q

what happens to pyruvate in aerobic conditions?

A

Aerobic oxidation. Pyruvate is converted into acetyl-CoA to be further metabolised int he citric acid cycle

39
Q

Where is pyruvate converted into Acetly-CoA?

A

In the mitochondrial matrix

40
Q

What is the enzyme which concerts pyruvate to Acetyl-CoA?

A

Pyruvate dehydrogenase which is a multi enzyme complex with lots of cofactors/enzymes

41
Q

What is the net reaction of converting pyruvate to acetyl-CoA?

A

Oxidative decarboxylation

42
Q

What happens with the energy from oxidation of pyruvate?

A

It is captured in NADH and used to add coenzyme a (CoA)

43
Q

What is the delta G of pyruvate oxidation?

A

-33.4kJ/mol

44
Q

What happens to pyruvate in anaerobic (low oxygen) conditions?

A

It is converted to lactate by lactate dehydrogenase using energy captured in NADH (energy is lost).The lacteal causes muscle fatigue

45
Q

Why does the anaerobic pathway of oxidation occur?

A

There are low concentrations of enzymes in cells asn during anaerobic oxidation coenzymes are oxidised (regenerated) in oxidative phosphorylation

46
Q

What happens is the lactate dehydrogenase reaction?

A

NAD is oxidised to produce sufficient NAD+ for the glyceraldehyde-3-phosphate dehydrogenase reaction so glycolysis can continue to generate ATP

47
Q

What happens to pyruvate in anaerobic conditions in yeast?

A

Anaerobic alcoholic formation - pyruvate is converted to ethanol and carbon dioxide to recycle NAD+

BIOC192 (38 decks)

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