Biochemistry - The Chemical Reactions of Living Cells, Volume 2 - D. Metzler 1980

Biosynthesis: How New Molecules Are Formed
Metabolic Loops and Biosynthetic Families

In this chapter, we explore the General Principles and strategies for the synthesis of A wide variety of carbon-containing compounds found in living organisms. Since green plants and autotrophic Bacteria are capable of producing all the carbon compounds they need directly from CO₂, we will examine the mechanisms they use to accomplish this. We will also address how other organisms manage to survive using such simple molecules as formate and acetate.

Biosynthetic (anabolic) pathways often run almost parallel to pathways of biological breakdown (catabolic) (Fig. 7-1). For instance, Catabolism begins with the hydrolytic Cleavage of polymer molecules, and the resulting monomers undergo further degradation into smaller two- and three-carbon fragments. Biosynthesis, conversely, starts with The formation of monomeric units from small molecules, which are subsequently linked together to form polymers. The mechanisms of individual biosynthetic and biodegradative reactions also frequently parallel one another. C—C bond-forming reactions in biosynthesis correspond to C—C bond-cleavage reactions in catabolism. Similarly, polymerization and Hydrolysis reactions share common features. Nevertheless, in most cases, clear-cut distinctions exist between biosynthetic and Catabolic pathways. Therefore, the primary principle of biosynthesis states that while biosynthetic pathways are linked to catabolic ones, they can differ significantly from them and are often catalyzed by an entirely different set of Enzymes.