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Introduction to Genetics & Biochemistry > Nitrogen Metabolism > Flashcards

Nitrogen Metabolism Flashcards

1
Q

Why does nitrogen need to be fixed?

A

So that it is in a usuable form for plants and animals who cannot use pure nitrogen gas.

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2
Q

How much of the earth’s atmosphere is nitrogen gas?

A

78%.

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3
Q

How much of the dry matter of living organisms is nitrogen?

A

9%.

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4
Q

What sort of bond is between the two atoms of nitrogen in a molecule of pure nitrogen gas?

A

A very strong triple bond.

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5
Q

What are the only organisms that can fix nitrogen?

A

A small subset of bacteria.

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6
Q

Where does nitrogen fixing bacteria live?

A

In nodules on the roots of legumes, where they live in a symbiotic relationship with the plant.

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7
Q

Why is the relationship between nitrogen-fixing plants and bacteria symbiotic?

A

The plants provide an anaerobic environment in their nodules and sugars for the bacteria.

In return the plant can use the ammonium (NH4+) made by the bacteria.

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8
Q

Denitrification allows bacteria to generate their own…?

A

…energy.

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9
Q

What weather can create ammonium?

A

Lightning.

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10
Q

Aside from lightning and bacteria, name another way in which nitrogen can be fixed?

A

In industrial processes.

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11
Q

Does the nitrogen we breathe serve any purpose for us?

A

No, we cannot use it, it is just breathed in and out.

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12
Q

Why is pure nitrogen gas (N2) very inert?

A

It has a very strong triple bond between the two atoms of nitrogen.

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13
Q

What three forms must nitrogen be in to be able to be incorporated into plants and animals?

A
  1. Nitrate (NO3).
  2. Nitrogen dioxide (NO2).
  3. Ammonium (NH4).
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14
Q

In the first step of nitrogen fixation, N2 is fixed by bacteria into…?

A

Ammonia (NH3).

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15
Q

What are the three main producers of ammonia and ammonium?

A

Bacteria, lightning and industry.

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16
Q

Most industrially fixed nitrogen comes from which process?

A

The Haber Process.

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17
Q

What is made in the Haber Process?

A

Fertilisers, explosives and plastics.

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18
Q

Describe the Haber Process.

A

Pure nitrogen gas (distilled from air) and hydrogen (from methane and steam) form ammonia, then nitric acid and nitrates.

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19
Q

What are the special conditions required for the Haber Process? Why?

A

Temperature over 500c, pressure over 300kPa and an iron catalyst are required ro provide enough energy to break the N-N triple bond.

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20
Q

Why do bacteria need anaerobic conditions to fix nitrogen?

A

Oxygen deactivates nitrogenase enzyme.

21
Q

In most nitrogen-fixing microorganisms, the eight high-potential electrons from from reduced…?

A

Recued ferrodoxin.

22
Q

How is the reduced ferrodoxin which donates eight high-energy electrons in natural nitrogen fixation produced?

A

In photosynthesis or oxidative processes.

23
Q

Describe what this reaction shows:

N2 + 8e- + 8H+ + 16ATP + 16H20 = 2NH3 + H2 + 16ADP + 16Pi.

A

The fixation of nitrogen into ammonia.

Two molecules of ATP are hydrolysed for each molecule transferred (8e- from ferrodoxin and 8H+), therefore 16ATP are hydrolysed from every molecule of N2 that is reduced.

24
Q

The reaction to reduce N2 to NH3 is very energy costly, requiring 16ATP for every molecule of N2 reduced. The ATP is not required to make the reaction thermodynamically favourable, so why is it needed?

A

To reduce the heights of the activation barriers along the pathway, making the reaction kinetically feasible.

25
Q

What sort of reaction does nitrogenase catalyse?

A

A redox reaction.

26
Q

Is the reduction of N2 to NH3 a slow reaction, or a fast one?

A

Very slow!

27
Q

What can inhibit the action of nitrogenase in the reduction of N2?

A

Oxygen.

28
Q

Why can’t nitrogen be fixed in the presence of oxygen?

A

Ferrodoxin prefers to bind to oxygen rather than nitrogen because it is an ‘easier’ reaction.

Nitrogenase is inhibited by oxygen.

29
Q

Nitrogen is essential for the synthesis of…?

A

…amino acids.

30
Q

What form of nitrogen is introduced to amino acids in the assimilation of nitrogen into biomolecules?

A

Ammonium (NH4+).

31
Q

G…………..e and g……………..e are essential in the assimilation of nitrogen into biomolecules.

A

Glutamate and glutamine.

32
Q

Glutamate is synthesised from ammonium and alpha-ketoglutarate - which cycle is this an intermediate of?

A

The citric acid cycle.

33
Q

Can glutamate and glutamine store excess nitrogen?

A

Yes, temporarily. They transanimate glutamate to glutamine.

34
Q

How does the cell save nitrogen and energy in the synthesis of amino acids from glutamine?

A

Feedback inhibition - the end products are inhibited if they start to overaccumulate.

35
Q

Which nitrogen-rich amino acid can be used for the synthesis of other amino acids?

A

Glutamine.

36
Q

Glutamate is a precursor for which three amino acids, as well as the main nitrogen donor for other amino acids?

A

Glutamine, arginine and proline.

37
Q

Similar amino acids are made from similar…?

A

…precursors.

38
Q

Where do the precursors for amino acid synthesis come from?

A

The citric acid cycle.

39
Q

Do essential amino acids or other amino acids tend to be more complex to synthesise?

A

Essential amino acids.

40
Q

What decided whether energy or amino acids are produced in the citric acid cycle?

A

Enzymes at key steps in the cycle - alpha-ketoglutarate and oxaloacetate.

41
Q

Amino acids can only be produced if enough ………………. is available?

A

Nitrogen.

42
Q

What happens in the citric acid cycle to amino acids that are not needed?

A

They are fed back into the citric acid cycle at certin points where they can be broken down and recycled.

43
Q

Which amino acids are made from oxaloacetate?

A

Aspartate, asparagnine, methionine, threonine, lysine and isoleucine.

44
Q

Which amino acids are made from pyruvate?

A

Alanine, valine and leucine.

45
Q

Which amino acids are made from phosphoenolpyruvate and erythrose-4-phosphate?

A

Tyrosine, phenylalanine and tryptophan.

46
Q

Which amino acids are made from alpha-ketoglutarate?

A

Glutamine, glutamate, proline and arginine.

47
Q

Which amino acids are made from 3-phosphoglycerate?

A

Serine, cysteine and glycine.

48
Q

Which amino acid is made from ribose-5-phosphate?

A

Histidine.

49
Q

Which five amino acids can give rise to other amino acids?

A

Phenylalanine, aspartate, threonine, glutamate and serine.

Introduction to Genetics & Biochemistry (21 decks)

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