The process is mostly confined to plants and bacteria.
Higher mammals use complex sulfur containing molecules from food.
Two important animo acids, Cysteine and Methionine, contain sulfur.
1/3 of all sulfur and 99% of all Sulfur Dioxide (SO2) entering the atmosphere is anthropogenic.
Of the anthropogenic portion, 2/3's from electric power production
In the atmosphere, sulfur dioxide is transformed to sulfur trioxide with molecular oxygen and then with water to sulfuric acid.
Step 1
Step 2
Without it, plants and animals cannot grow or carry on molecule building syntheses
Their chemical process can be nitrogen limited
Sources of nitrogen
Primary source - the atmosphere 78% N2
N2 cannot be used by plants or animals
Conversion from N2 to NH3, NH4+, NO2-, NO3-, is required
Ammonia (NH3) can be used by all plants and animals for conversion into nitrogen containing complex molecules.
N2 has a triple bond with a bond energy of 940 kJ/mole
Nitrogen fertilizer is frequently ammonia based and is prepared by catalytic hydrogenation of N2.
Conversion of N2 to ammonia (NH3) is a very energy expensive process biologically (or energy demanding industrially) Breaking a 940 kJ/mole bond for 2NH3 formed
This process requires an enzyme system (Nitrogenase System).
It consists of two proteins & Fe4S4 iron-sulfur cluster and a Mo cofactor
Thus the oxidation of N2 to NH3 requires:
C, O, N, S, Fe, Mo, P, H2O, e-, H+, and ATP
and all the know how stored in DNA + a viable living organism
(DNA code is ~24,000 base pairs for nitrogen fixation, 18 genes)
{Note : Enzyme is inhibited by O2 and nodule on legumes exclude O2 while N2 fixation is accomplished. It is thought that if nodules exist they will be inhabited by these bacteria}
All plants and bacteria can reduce ammonia (NH3)to nitrate (NO3-)
Most plants and animals transform nitrate to
ammonia using the same steps also:
Carried out by Nitrate Reductase which includes Fe2S2
Most plants, animals, and bacteria share ammonia utilization pathways
This is why when you provide a plant NO3- or NH3 directly they can readily use it.
At pH 7, ammonia exists in ammonium ion form NH4+
Why? Remember pH and the equilibrium of water?
All organisms take ammonia to glutamate or carbamoyl phosphate
Conversion is accomplished by:
Plants in which nitrogen fixing bacteria function
alfalfa, clover, peas, beans, other legumes algae (glue-green)
Other plants require water soluble forms of nitrogen to grow
Reduction from Soluble nitrogen to N2 is denitrification
many bacteria in decay perform this task
As plants and animals decompose, they contribute water soluble nitrates to the soil making it available to the next generation of plants and to other plants
Nitrogen depletion occurs when land is planted with
soluble nitrogen depleting plants repeatedly
Example corn, wheat, oats, etc.
70 kg person (154 lb)
400g of protein synthesis per day
400g of protein broken down per day
100g of protein intake per day
100g of protein excreted per day
500g of protein available per day
The half-life of a nitrogen atom in the body is 2 hrs. to 6 months depending on where it gets incorporated.
Why the difference?
In active chemistry, such as enzymes, molecules are stable for a few hours as a particular proteinIn structural collagen or hair tissue, these structural materials are not renewed for longer times
Overall turnover of proteins and nitrogen seems to have a 1st order kinetic rate. That indicates that it is a random process. Why?
Since proteins are the chemical producers of the body and are damaged by chemical and physical use perhaps this is a quality control step to maintain structural integrity. DNA can be repaired but proteins are not once they are made. What are the ramifications of this process?
Protein turnover also represents a route for cellular adaptation to altered environmental conditions.
NOx's also are produced and released into the air by the burning of fuels: wood, coal, gas, etc.
We will discuss why this is pollution when we discuss air pollution
