L28 - Nitrogen Metabolism 1 Flashcards

1
Q

State the 6 organic forms Nitrogen can be found in

A
N2
N2O
NH4+
NH3
NO3-
NO2-
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2
Q

Define each:

a) Nitrogen fixation
b) Nitrate assimilation
c) Nitrification
d) De-nitrification
e) Ammonia assimilation

A

a) Nitrogen fixation - nitrogen to ammonia
b) Nitrogen assimilation - nitrate to nitrite to ammonia
c) Nitrification - ammonia to nitrite to nitrate
d) De-nitrification - nitrate to nitrite to NO2 to N2
e) Ammonia assimilation - ammonia to glutamate

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3
Q

What is the most important bacteria in nitrogen fixation and where is it found?

A

Rhizobium - found in the root nodules of legumes, in a symbiotic relationship

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4
Q

What enzyme do nitrogen fixing bacteria use and what are its 2 components?

A

Nitrogenase

  • nitrogenase
  • nitrogenase reductase
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5
Q

What 2 components does nitrogen fixation require aside from the enzyme?

A

12-18 units if ATP (probably 2 per electron transferred)

The reducing power of ferredoxin

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6
Q

Give the 3 other names Nitrogenase reductase is known as

A

Component II
Fe-protein
Fe-S protein

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7
Q

What must happen to ferredoxin for the reaction to continue?

A

Ferredoxin must be reduced if reaction is to continue

In photosynthetic organisms it is reduced in light reactions of photosynthesis. In others use NADPH, H2, HCOOH or pyruvate

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8
Q

How is ferredoxin reduced?

A

Nitrogenase reductase accepts electrons from ferredoxin, reducing it, then passes the electrons onto nitrogenase to reduce itself back

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9
Q

What are the other to names for Nitrogenase (the component part)

A

Component I

Mo-Fe protein

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10
Q

Describe how nitrogenase is reduced/oxidise

A

Nitrogenase is reduced by accepting electrons from Nitrogenase reductase. It is the re-oxidised by passing them the N2 and H+ to form ammonia

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11
Q

Where does ammonia ammisilation occur?

A

Plants and micro-organism

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12
Q

Briefly state the 2 methods of ammonia assimilation

A

1) Glutamate dehydrogenase (GDH)
- no ATP needed
- high Km for NH3

2) Glutamine synthetase (GS + GOGAT)
- uses ATP
- low Km for NH3

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13
Q

How does Km relate enzyme activity to substrate concentration?

A

Km is the [S] when enzyme activity (v) = Vmax/2

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14
Q

Which of the above reactions is the least efficient, energetically?

A

Both reactions give the same end product but the GS+GOGAT reaction is less efficient because it requires ATP

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15
Q

Why might an organism be forced to use the less efficient reaction?

A

GS+GOGAT works at very low [NH3] so use of ATP worthwhile in order to be able to trap the NH3 at these low concentrations

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