Biosynthesis
Biosynthesis is an essential stage in metabolism where building blocks used in the synthesis of cell macromolecules and membranes are produced from simpler precursors. It is preceded by a fueling (catabolism stage and followed by polymerisation and assembly of building blocks into cell components.
Biosynthesis, takes place within living cellss and is generally catalysed by enzymes. The reactions are generally organised in sequential steps called biosynthetic pathways, which branch from a metabolic network known as central metabolism.
The prerequisites for biosynthesis are:
- Thirteen precursor carbon-skeletons
- Energy (usually in the form of ATP)
- Enzyme catalysts
- Reduction equivalents (in the form of hydrogen carried on the coenzymes NADH, NADPH and others)
- Nitrogen in the form of ammonium ion.
- Reduced forms of sulfur in some amino acids
Important and widely known products of biosynthesis include amino acids, nucleotides, and , vitamins but all components of living beings depend on this process. Biosynthesis is harvested by the biotechnology industry to manufacture flavoring compounds such as mono sodium glutamate and lysine, vitamins, and therapeutic proteins such as insulin and growth hormones.
Representative biosynthetic pathway
The amino acid glutamate is a common component of proteins. It can be formed by a short pathway of two steps that illustrates the features of a typical biosynthetic pathway.
The inputs of the pathway are carbon from 2-oxoglutarate (a metabolite in the TCA cycle portion of central metabolism), NADH (hydrogen carrier co-enzyme) and ATP.
Glutamine is an intermediate in the pathway.
Although the pathway seems to start with its product glutamate , the second step generates two glutamate molecules. Thus the net effect is conversion of an organic acid precursor with assimilation of nitrogen into an amino acid monomer that can used in protein synthesis.
