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Cellular and Molecular Biology > Lecture 30: The fate of Pyruvate REVISIT!! > Flashcards

Lecture 30: The fate of Pyruvate REVISIT!! Flashcards

26/11/2024

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1
Q

Does glycolysis require oxygen?

A

NOOO

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2
Q

How is pyruvate oxidised?

A

It has a carbon dioxide removed and is hence converted into acetyl-CoA

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3
Q

Did Harden and Young find out that inorganic phosphate is a limiting factor for photosynthesis?

A

Yes

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4
Q

Do we have to worry about running out of ATP?

A

No, because there is a constant interconversion between ATP and ADP

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5
Q

What happens if cofactors, like NAD+, run out?

A

Then glycolysis stops

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6
Q

What is done to pyruvate to restore the supply of NAD+?

A
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7
Q

What can pyruvate be converted to?

A

Ehanol in yeast cells, lactate in the muscles, acetyl coA(which can be further oxidised) under aerobic conditions in citric acid cycle

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8
Q

How is NAD+ regenerated aerobically?

A
  • Pyruvate us oxidised to acetyl coA in the citric acid cycle.
  • In the electron transport chain, NADH transfers electrons to Oxygen , forming water and regenerating NAD+.

-

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9
Q

Is it true that the regenration of NAD+ requires reduction of another compound?

A

Yes

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10
Q

What do anaerobic conditions lead to ?

A

fermentation

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11
Q

Define fermentation

A

“An ATP producing process in which organic compounds act both as electron donors and as electron acceptors”

(Glucose oxidised to pyruvate (glucose donates e-)
)

( Pyruvate reduced to ?? (pyruvate accepts e-)
)

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12
Q

when is lactate the fermentation product?

A

In animal muscle, red blood cells, some cancer cells, lactobacillus:

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13
Q

when is ethanol the fermentation product?

A

In plants and yeast

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14
Q

In which organisms can the fermentation product be: Acetate and other carboxylic acids, hydrogen etc?

A

In Various other microorganisms

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15
Q

How often are animal and plant cells usually anaerobic?

A

Animal and plant cells usually temporarily anaerobic

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16
Q

When are animal cells usually anerobic?

A

During strenuous exercise

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17
Q

Are cancer cells usually anaerobic?

A

Yes

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18
Q

Why are red blood cells anaerobic?Because they don;t have a mitochondria

A
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19
Q

Give some examples of environments that are permannetly anaerobic

A

Bacteria in marine and lake sediments, marshes, animal gut

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20
Q

What was the early atmosphere like?

A

Anaerobic, so glycolysis could be run

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21
Q

Why do we need to further oxidise pyruvate in the citric acid cycle?

A

Because this is the only way to release all of glucose’s energy, as the majority of pyruvate’s energy will still be stored in pyruvate at the end of glycolysis.

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22
Q

So which produces more ATP anaerobic respiration or aerobic respiration?

A

Aerobic respiration

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23
Q

Where does the citric acid cycle take place?

A

In the mitochondrial matrix

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24
Q

How does pyruvate reach the mitochondrial matrix?

A

It is cotransported there with H+ ions

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25
Q

What happens after pyruvate is cotransported into the mitochondria matrix?

A

It is decarboxylated, then converted into acetyl coA. This uses up a NAD+ and regenerates an NADH

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26
Q

Why were original studies of the movement of pyruvate from the cytosol to the mitochondrial matrix conducted on liver and on pigeons?

A

Because they’re both incredibly rich in mitochondria

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27
Q

After pyruvate is converted into acetly coA, what can happen?

A

The acetyl can then enter the citric acid cycle and couple with 4C oxaloacetate to form 6C Citrate

28
Q

What happens after ocaloacetate is converted into citrate?

A

2 Carbon dioxide’s are lost, and oxaloacetate is constantly reformed, and the cycle repeats over and over again

29
Q

What happens when fatty acids are broken down into acetyl coA?

A

They’re oxidised in exacrtly the same way that acetly coA from glucose is (integration point between the 2 main sources of energy, fatty acids and sugars)

30
Q

Is it true that 2 carbon dioxide’s are released for each acetyl group?

A

Yes

31
Q

What is the reactive group of coenzyme A/

A

The SH group

32
Q

Draw out the structure of coenzyme A

A
33
Q

What part of coenzyme A links to the acetate group?

A

The SH group

34
Q

Draw out the structure of acetyl coA

A
35
Q

Draw out the reaction for the conversion of pyruvate to acetyl CoA

A
36
Q

How do we know that the reaction for the conversion of pyruvate to acetyl CoA is irreversible?

A

Because the ΔG &laquo_space;0
(no going back to glucose)

37
Q

What catalyses the conversion of pyruvate to acetyl CoA?

A

pyruvate dehydrogenase multienzyme complex

38
Q

Is it true that Pyruvatedehydrogenase complex is very big?

A

Yes, it is 4-10 x106 kDa
i.e. larger than ribosomes

39
Q

How many different enzymes does the pyruvate dehydrogenase complex consist of?

A

3

40
Q

What are the 3 enzymes that the pyruvate dehydrogenase complex consists of?

A

pyruvate dehydrogenase component (E1)

dihydrolipoyl transactetylase (E2)

dihydrolipoyl dehydrogenase (E3)

41
Q

What is the function of E1?

A

decarboxylation of pyruvate

42
Q

What is the function of E2?

A

Reduction of NAD+ to NADH + transfer of the acetyl group to CoA

43
Q

What is the function of E3?

A

Reoxidation + the regeneration of the oxidised form of lipoamide

44
Q

Describe E1: Pyruvate dehydrogenase component

A
  • Derived from vitamin B1
  • Found in the outer seed coats of cereals incl. rice.
  • Deficiency in man
    results in “beri-beri”
  • Not simple process, requires TPP cofactor, which particpates in the decarboxylation of
    pyruvate
  • Hydrogen is lost, resulting in a negative C
45
Q

Describe E2: Dihydrolipyol transacetylase

A

Acetyl group is picked off TPP and transferred to CoA ADD MORE DETAIL

As disulfide has been reduced, it has to be re-oxidised

46
Q

Describe E3: Dihydrolipyol dehydrogenase

A

Reoxidation of disulphide in lipoamide

Reoxidation of FADH2 generates 1 NADH

47
Q

Which reactions are catalysed by the pyruvate dehydrogenase
multi-enzyme complex

A

1)

48
Q

What is the equation that represents the conversion of pyruvate to acetyl-CoA?

A

Pyruvate + CoA-SH + NAD+ —–> Acetyl-CoA + CO2 + NADH

49
Q

What is a multienzyme complex?

A

A group of 2 or more non-covalently associated enzymes that catalyse two or more sequential steps in a metabolic pathway

50
Q

What are the advantages of multienzyme complexes?

A
  • Product of the first reaction in the sequence remains attached
  • Serves directly as a substrate for the second reaction
  • Therefore rate of second reaction not limited by diffusion
  • Can channel intermediates between successive enzymes, thereby minimising side reactions
  • The reactions may be coordinately regulated
51
Q

How is pyruvate dehydrogemase controlled?

A

By phosphorylation. Kinase phosphorylates the enzyme. Kinase is stimulated by high energy status (AcetylCoA, ATP and NADH
) and inhibited by low energy status (ADP and NAD+
)

52
Q

The Sparker Effect

A
53
Q

Who discovered the citric acid cycle?

A

Szent-Györgyi and Krebs (both got Nobel prizes)

54
Q

Describe the sparker effect

A
  • Mince liver to release its enzymes, add pyruvate, and measure oxygen consumption- should find that not much happens
  • Then add the trace of an organic acid with the pyruvate and mince liver, Should find that oxygen consumption is higher.
  • Realised that something must be being oxidised. The organic acids weren’t used up so it could not be them .
  • The interpretations from this were that; organic acids work catalytically and one molecule of the organic acid can spark oxidation of an infinite amount of pyruvate
  • They repeated the experiment and realised that succinate accumulated and the same thing happened if a trace amount of fumurate was added. This proved that the pathwya was cyclic
55
Q

What can organic acids include?

A

Organic acids: citrate, fumarate, malate or succinate

56
Q

What is malonate a potent inhibitir for?

A

Malonate was found to be a potent inhibitor of respiration in all animal tissues

57
Q

What are the other names of the citric acic cycle?

A

Krebs cycle

Tricarboxylic Acid Cycle

TCA cycle
58
Q

What are the principle negative regulators of the citric acid cycle?

A

ATP and NADH are the principal negative regulators . The need for energy and for carbon skeletons is the main positive regulator

59
Q

If oxaloacetate is depleted from the citric acid cycle, what will happen?

A

The cycle will stop

60
Q

How is the withdrawal of citric acid cycle intermediates rectified?

A

Achieved by anaplerotic (ana pleros: to fill up, replenish) reactions. In humans, the main anaplerotic reaction introduces more oxaloacetate into the cycle, via carboxylation of pyruvate: Pyruvate+ CO2+ATP+H2O 🡪 oxaloacetate+ADP+Pi+2H+

(Catalysed by pyruvate carboxylase )

61
Q

is is true that ‘Glucogenic amino acids can be used in anaplerotic reactions if needed
Ketogenic amino acids can not’?

A

Yes

62
Q

is it true that Citric acid cycle is a shared pathway for breakdown of carbohydrates, fats and amino acids?

A

Yes

63
Q

is it true that the citric acid cycle mainly generates reduced coenzymes
?

A

Yes

64
Q

why are intermediates sometimes taken out of the citric acid cycle?

A

For biosynthesis i.e amino acid synthesis

65
Q

Do fats make sugar?

A

No

66
Q
A

Cellular and Molecular Biology (33 decks)

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