Biological Stoichiometry: Is it Approximation or Precise Science?
Biological Stoichiometry: Is it Approximation or Precise Science? Let us first recall the freshman (or even high school) chemistry that normally introduces students to the stoichiometry of chemical reactions. Stoichiometry is defined as the calculation of relative quantities of reactants and products in chemical reactions. The chemical stoichiometry is always well defined and stems from the mass conservation law that is outside of any doubts. Brutto formulae of chemical compounds contain integers (numbers without a fractional component), such as H2O for water or C2H4O2 for acetic acid. There is always a limited number of chemical elements, say, only three (C, H, O) for aliphatic organic compounds. Reaction stoichiometry is expressed schematically using integers, e.g. methane oxidation: CH4 +2O2 CO2 +2H2O The biological stoichiometry is more complex and less certain. For cell mass we have various versions of brutto formulae, for example: CH1.9O0.5N0.2P0.01…, where ellipsis “…” indicates that the real full formula should be much longer. • There are no integers, only the fractional numbers at each element implying a low degree of precision. The reaction stoichiometry for biological processes involving the growth of cells is also less certain with stoichiometric coefficient expressed as fractional numbers, never integers. • We understand the principal reason behind the difference between chemical and biological stoichiometry: any cell is much more complex than any individual chemical compound. However less trivial questions remain to be important and not yet explicitly answered
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