The fueling reactions essentially bring together all the raw materials needed to initiate and maintain all other cellular processes. The production of precursors and energy is mostly accomplished by catabolic processes dial involve the degradation of substrate molecules. The three remaining primary pathways—biosynthesis, polymerization, and assembly—depend on anabolic metabolism, in which precursor compounds are put together for the creation of larger molecules (polymers) needed for assembly of cellular structures (see Figure 2-11),
Biosynthetic processes use the 12 precursor products in dozens of pathways to produce nearly 100 different building blocks such as amino acids, fatty adds, sugars, and nucleotides (see Figure 2-11). Many of these pathways are highly complex and interdependent, whereas other pathways are almost completely independent. In many cases, the enzymes that drive the individual pathways are encoded on a single mRNA molecule that has been cotranscribed from contiguous genes in the bacterial chromosome (i.e., an operon).
As discussed with the fueling pathways, bacterial genera and species vary extensively in their biosynthetic capabilities. Knowledge of these variations is necessary to ensure the design of optimal conditions for growing organisms under laboratory conditions. For example, some organisms may not be capable of synthesizing a particular amino acid that is a necessary building block for several essential proteins. Without the ability to synthesize the amino acid, the bacterium must obtain that building block from the environment. Similarly, if this organism is to be grown in the microbiology laboratory, this need must be fulfilled by supplying the amino acid in culture media.
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