Microbes and Metabolism - Environmental Biotechnology: Theory and Application - page 17

energy and synthetic needs of the cell at that time. A related pathway, sharing
some but not all of the reactions of glycolysis, and which operates in the opposite
direction is called gluconeogenesis. Pyruvate can continue into the TCA cycle
whose main function is to produce and receive metabolic intermediates and to
produce energy, or into one of the many fermentation routes.
The principles of glycolysis are universal to all organisms known to date,
although the detail differs between species. An outline of glycolysis, the TCA,
and its close relative the glyoxalate, cycles is given in Figure 2.1, together with an
indication of the key points at which the products of macromolecule catabolism,
or break-down, enter these central metabolic pathways. The focus is on degrada-
tion rather than metabolism in general, since this is the crux of bioremediation.
A description of the biological macromolecules which are lipids, carbohydrates,
nucleic acids and proteins are given in the appropriate Figures 2.2-2.5.
Not all possible metabolic routes are present in the genome of any one
organism. Those present are the result of evolution, principally of the enzymes
which catalyse the various steps, and the elements which control their
expression. However, an organism may have the DNA sequences, and so have
Figure2.1 Glycolysis,theTCAandglyoxalatecycles