Fundamentals of Microbiology

3.2.2 Biochemical Pathways of Energy Use ( Anabolism)

Biosynthesis of Polysaccharides

Microorganisms synthesize sugars and polysaccharides. The carbon atoms required to synthesize glucose are derived from the intermediates produced during processes such as glycolysis and the Krebs cycle and from lipids or amino acids. After synthesizing glucose (or other simple sugars), bacteria may assemble it into the more complex polysachharides.

Biosynthesis of Lipids

Because lipids vary in chemical composition, they are synthesized by a variety of routes. Cells synthesize fats by joining glycerol and fatty acids. The glycerol portion of the fat is derived from dihydroxyacetone phosphate, an intermediate formed during glycolysis. Fatty acids, which are long-chain hydrocarbons (hydrogen linked to carbon), are built up when two carbon fragments of acetyl CoA are successively added to each other.

Biosynthesis of Amino acids and proteins

Amino acids are required for protein biosynthesis. Some microbes, such as E.coli, contain the enzymes necessary to use starting materials, such as glucose and inorganic salts, for the synthesis of all the amino acids they need. Organisms with the necessary enzymes can sysnthesize all amino acids directly or indirectly from intermediates of carbohydrate metabolism. Other microbes require that the environment provide some preformed amino acids.

One important source of the precursors (intermediates used in amino acid synthesis is the Krebs cycle. Adding an amine group to pyruvic acid or to an appropriate organic acid of the krebs cycle converts the acid into an amino acid. This process is called amination.

Most amino acids within cells are destined to be building blocks for protein synthesis. Proteins play major roles in the cell as enzymes, structural components, and toxins.