Dynamic State of Body Constituents - Concept of Metabolism
All living organisms, be it a simple bacterial cell, a protozoan, a plant or an animal, contain thousands of organic compounds. These compounds or biomolecules are present in certain concentrations. All the biomolecules have a turn over. This means that they are constantly being changed into some other biomolecules. This breaking and making is through chemical reactions constantly occurring in living organisms. Together all these chemical reactions are called metabolism.
Each of the metabolic reactions results in the transformation of biomolecules. A few examples for such metabolic transformations are removal of CO2 from amino acids, making an amino acid into an amine, removal of amino group in a nucleotide base, hydrolysis of a glycosidic bond in a disaccharide, etc. We can list tens and thousands of such examples.
Majority of these metabolic reactions do not occur in isolation but are always linked to some other reactions. In other words, metabolites are converted into each other in a series of linked reactions called metabolic pathways.
Flow of metabolites through metabolic pathway has a definite rate and direction. This flow is called the dynamic state of body constituents. What is most important is that this interlinked metabolic traffic is very smooth and without a single reported mishap for healthy conditions.
Another feature of these metabolic reactions is that every chemical reaction is a catalysed reaction. There is no uncatalysed metabolic conversion in living systems. Even CO2 dissolving in water, a physical process, is a catalysed reaction in living systems. The catalysts which hasten the rate of a given metabolic conversation are also proteins. These proteins with catalytic power are named enzymes.