Biochemistry attempts a detailed analysis of the reaction sequences important in growth and biosynthesis and the ways in which they are regulated. It is also concerned with the chemical substances involved. These biochemical reactions are all brought about by biological catalysts, i.e. the enzymes. The synthesis of these enzymes and its regulation are brought about by the nucleus and are therefore under genetic control. Thus the combined biochemical–genetic system is central whenever consideration is given to microbial behaviour. The subject is therefore extensive and complex. Those interested should consult a suitable textbook, such as Conn & Stumpf's Outlines of Biochemistry (1976). However, caution is needed because there are differences between animal and microbial biochemistry, as well as differences between ukaryotic and prokaryotic biochemistry.

Enzyme reactions

The basis of life processes is the existence of enzymes – catalysts that accelerate chemical reactions leading to the production of substances, with large or small molecules, that are the basis of cell structures and cell metabolism.

Important features of living cells are (1) the large number of enzymes commonly involved, perhaps 2000 or more, (2) the existence of chain reactions in which enzymes work together, and (3) the close control of these systems which is exerted at different levels. In development work, increases in production seem to be brought about mainly by alterations to these regulatory systems.

Consider, for instance, the formation of acetoacetate from acetate. This can be carried out chemically by heating ethyl acetate with sodium, which catalyses a multi-step reaction. Enzymically it is produced by a complex reaction that carboxylates the acetyl units to malonyl units, pairs of which are then condensed and decarboxylated.