Transcript LECT 29 NitrogFix

Nitrogen Fixation
Our goal is to learn how N2 an inert gas, becomes
part of the structure of organic molecules
Secondly, to study the function of nitrogen
compounds in plants and bacteria
To study the nitrogenase complex and
learn its secrets for fixing nitrogen
How Powerful is Nitrogen Gas?
Haber Process
300 atm
N2(g) + 3H2(g)
2NH3(g) + 92 kJ
450oC (Super heated Steam)
Why is Nitrogen so Hard to Split?
N N
Triple bond
945 kJ per mole
(C-C Bond is 347 kJ per mole)
N N + 2e + 2H+
HN=NH + 2e + 2H+
H2N-NH2 + 2e + 2H+
HN=NH
H2N-NH2
2NH3
Valence State is a Key to the Chemistry of N
HNO3
+5
Nitrates
+4
NO2(g)
HNO2
+3
+2
NO
OXIDATION
Nitrites
Nitric oxide
N2O(g) +1
N2
0
HN=NH
REDUCTION
Diatomic
-1
H2N-NH2 -2
NH3
Ammonia
-3
Nitrogen Compounds in Plants and Bacteria
Nitrite Reduction
Nitrate
Reduction
NO3
Return
nitrogen
compounds
to N2
Denitrification
NO2
Energy
Nitrification
(Soil bacteria)
N2(g)
NH3
Energy
N2 fixation (reduction)
Plants produce NH3 by reducing nitrates and nitrites
Soil bacteria derive energy by oxidizing NH3
Nitrogen Metabolism by Species
Bacteria
Plants
Animals
Nitrogen fixation
Yes
No
No
Nitrate Reduction
Yes
Yes
No
Nitrite Reduction
Yes
Yes
No
Nitrification
Yes
No
No
Denitrification
Yes
No
No
NH3 Assimilation
Yes
Yes
Yes
Amino Acid Synthesis
Yes
Yes
Yes
Remarkable Nitrogenase
Biological Reaction
N2 + 8H+ + 8e- + 16ATP + 16H2O
2NH3 + 16ADP + 16Pi + H2 + 16H+
Nitrogenase Complex (nif gene cluster)
Nitrogenase (Mo, Fe protein)
Nitrogenase Reductase (Fe protein)
Nitrogenase Dialogue
Where do we find Nitrogenase?
Nitrogenase is present in certain bacterial species referred
to a diazotrophs. The legumes (peas, beans, alfalfa, etc.)
have root nodules infested with the nitrogen fixing
bacteria, Rhizobium. Free living bacteria such as
azobacter vinelandii can also fix nitrogen.
What is meant by symbiosis in nitrogen fixation?
Symbiosis means living together for mutual benefit. The
bacteria provide the plant with NH3 and the plant prevents
oxygen from interfering with the fixation reaction.
What interferes with nitrogen fixation?
Oxygen is the major factor. Nitrogen fixation can take
place only in the total absence of O2
How does a plant overcome oxygen interference?
By synthesizing a heme protein, leghemoglobin, which
like other hemoglobins, has a high affinity for binding
oxygen….what is called “sequestering” the oxygen.
Why such as funny name?
The name gives the origin of the protein. It is made in
legumes, hence leghemoglobin. The heme group of the
hemoglobin is made in the bacteria.
Why are there two components in the nitrogenase complex
One component holds the N2 molecules, the
other passes electrons. Nitrogenase is a two-step energy
machine in which electrons are boosted to a higher
reducing potential (Nitrogenase reductase or Fe-protein)
and then passed to the N2 bound to the MoFe-protein
SHOW ME
Electron Transfer “Pump”
Dinitrogenase
A c t iv a t e d
0 .4 0
Nitrogenase
MoFe-Protein
M o
M o -H
F d
-eF d
R
R
M o -H
0 .2 9
e-
A T P
N=N
H
H - M o -H
A D P
H
H2
Dinitrogenase Reductase
Reductase
Fe-Protein
H -M o = N = N
Fd -e -
M o
R
R e-
Fd
A TP
ADP
H -M o = N -N H 2
e + H+
e+
Fd-e-
H+
R
NH3
R e-
Fd
A TP
ADP
M o = N
NH3
e+
H+
3 Gateways to
Biological Molecules
CO2 ATP
Carbamoyl
phosphate
Arginine
Urea
NH3
Aspartate
Asparagine
None
The only inorganic
nitrogen source for
mammals is NH3
a-Ketoglutarate
Glutamate
Other
amino
acids
Of the 3, the most versatile is glutamine
Glutamate
Glutamine
Purine nucleotides,
Cytidine nucleotides
Amino sugars,
Tryptophan, Histidine
Pyrimidine nucleotides
Rapid Quiz
• What key biocompound allows a bacterium,
a fungus, or a hippopotamus to convert
carbohydrates and amino acids into fat?
• Based on your answer, show how the
carbons in the amino acid alanine and
glucose become carbons in cholesterol
• Outline a path to show how the carbons in
phenylalanine become the carbons in stearic
acid and glucose.
Answer
Aminoacids
Carbohydrates
Acetyl-CoA
Fatty acids
Cholesterol
Triacylglycerols
Acylglycerolphosphates
Sphingolipids
Alanine
Glucose
Stearate
Pyruvate
Acetyl-CoA
HMG-CoA
Mevalonate
Isopentenyl-PPi
Cholesterol
Phenylalanine
Fumarate
Acetoacetate
L-malate
Acetyl-CoA
Tyrosine
p-hydroxyphenylpyruvate
OAA
Malonyl-CoA
Homogentisate
PEP
Maleyl-acetoacetate
Palmitate
Gluconeogenesis
Stearate
Fumaryl-acetoacetate
Glucose