1

1 molecule fructose 6-phosphate

Figure 6.28 The Calvin Cycle The Calvin cycle has three essential stages: (1) incorporation of CO2 into an organic compound; (2) reduction of the resulting molecule; and (3) regeneration of the starting compound.

Figure 6.28 The Calvin Cycle The Calvin cycle has three essential stages: (1) incorporation of CO2 into an organic compound; (2) reduction of the resulting molecule; and (3) regeneration of the starting compound.

6.10 Anabolic Pathways—

Synthesizing Subunits from Precursor Molecules

While prokaryotes as a group are highly diverse with respect to the compounds they use for energy, they are remarkably similar when comparing their biosynthetic processes. They synthesize the necessary subunits using specific anabolic pathways that use ATP, reducing power in the form of NADPH, and the precursor metabolites formed in the central metabolic pathways (figure 6.29). Anaplerotic reactions, which bypass certain steps of the central metabolic pathways, can be used to replenish some of the intermediates drawn off for biosynthesis. Once the subunits are synthesized, they can be assembled to make

Cell constituents macromolecules. Various different macromolecules can then be joined to form the structures making up the cell.

Organisms lacking one or more enzymes in a given pathway must have the end product of that pathway provided from an external source. This is why fastidious bacteria such as lactic acid bacteria require many different growth factors. ■ fastidious, p. 91

Lipid Synthesis

Synthesis of most lipids in microorganisms can be viewed as having two essential components—fatty acid synthesis and glycerol synthesis. Synthesis starts with transfer of the acetyl group of acetyl-CoA to a carrier protein called acyl carrier protein (ACP). This carrier serves to hold the fatty acid chain as it is elongated by progressively adding 2-carbon units. When the newly synthesized fatty acid reaches its required length, usually 14, 16, or 18 carbons long, it is released from

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