. Biological order. Biology. BIOLOGICAL ORDER increases the fitness between the bacterium and its environment. It is why this process has been, for a long time, called enzymatic adaptation. It is now described as an induced biosynthesis of enzyme. Let us now consider the reverse process. Repression. The bacterium Escherichia coli is able to grow in a synthetic medium devoid of any amino acid. Such a bacterium is therefore able to synthesize all its building blocks, or essential me- tabolites, and, among them, the amino acid methionine. The last step in the synthesis of methionine is catalyzed
. Biological order. Biology. BIOLOGICAL ORDER increases the fitness between the bacterium and its environment. It is why this process has been, for a long time, called enzymatic adaptation. It is now described as an induced biosynthesis of enzyme. Let us now consider the reverse process. Repression. The bacterium Escherichia coli is able to grow in a synthetic medium devoid of any amino acid. Such a bacterium is therefore able to synthesize all its building blocks, or essential me- tabolites, and, among them, the amino acid methionine. The last step in the synthesis of methionine is catalyzed by an enzyme called methionine synthase. When growing in a synthetic medium, the bacteria contain methionine synthase. Of course they have to. For in the absence of methionine synthase, they are unable to synthesize methionine. And in the absence of methionine, they are unable to synthesize proteins, that is, to grow. The enzyme methionine synthase is actually present (Figure 12). What happens when the growth © cysteic acid—H*cysteine " "t" ^ homosenne C SO, C SH C S C C—OH II C NHg C NH2 ^ ^ _ . COOH COOH COOH C NHj C — NHj COOH. C S —CH3 I c I C—NH, I COOH homocystine 0 methionine METHIONINE SYNTHASE Figure 12. The Synthesis of the Amino Acid Methionine. [38]. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lwoff, André, 1902-. Cambridge, M. I. T. Press
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