L28 - Nitrogen Metabolism 1 Flashcards
State the 6 organic forms Nitrogen can be found in
N2 N2O NH4+ NH3 NO3- NO2-
Define each:
a) Nitrogen fixation
b) Nitrate assimilation
c) Nitrification
d) De-nitrification
e) Ammonia assimilation
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
What is the most important bacteria in nitrogen fixation and where is it found?
Rhizobium - found in the root nodules of legumes, in a symbiotic relationship
What enzyme do nitrogen fixing bacteria use and what are its 2 components?
Nitrogenase
- nitrogenase
- nitrogenase reductase
What 2 components does nitrogen fixation require aside from the enzyme?
12-18 units if ATP (probably 2 per electron transferred)
The reducing power of ferredoxin
Give the 3 other names Nitrogenase reductase is known as
Component II
Fe-protein
Fe-S protein
What must happen to ferredoxin for the reaction to continue?
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
How is ferredoxin reduced?
Nitrogenase reductase accepts electrons from ferredoxin, reducing it, then passes the electrons onto nitrogenase to reduce itself back
What are the other to names for Nitrogenase (the component part)
Component I
Mo-Fe protein
Describe how nitrogenase is reduced/oxidise
Nitrogenase is reduced by accepting electrons from Nitrogenase reductase. It is the re-oxidised by passing them the N2 and H+ to form ammonia
Where does ammonia ammisilation occur?
Plants and micro-organism
Briefly state the 2 methods of ammonia assimilation
1) Glutamate dehydrogenase (GDH)
- no ATP needed
- high Km for NH3
2) Glutamine synthetase (GS + GOGAT)
- uses ATP
- low Km for NH3
How does Km relate enzyme activity to substrate concentration?
Km is the [S] when enzyme activity (v) = Vmax/2
Which of the above reactions is the least efficient, energetically?
Both reactions give the same end product but the GS+GOGAT reaction is less efficient because it requires ATP
Why might an organism be forced to use the less efficient reaction?
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
