The major NP pathways

As is explained in Chapter 9, the overall classificatiom of naturally made chemicals into two classes, now commonly known as primary and secondary, first suggested by Sachs rso years ago, and subsequently defined more clearly by Kossel 50 years later, has been very rmhelpful. There are not two classes of chemicals made by plants and microbes. In Chapter 9, it is argued that some NP pathways contribute to the production of another class of substance, substances that have been selected on the basis of their physicochemical properties.5 Whereas NPs are selected on the basis of their biological activity (or more precisely their biomolecular properties, as outlined in Chapter 5), some substances made by what have traditionally been considered to be NP pathways serve as colours or as membrane components or play various other roles determined by their physicochemical properties. Hence, the NP pathways are pathways that make NPs, but these pathways are not used exclusively for this purpose. This lack of exclusivity has some interesting evolutionary implications which are discussed in Chapter 9. 

The fact that there are tens of thousands of NPs known might seem extremely off-puttingwhen one first approaches NP biosynthesis. All the details and all the facts about the biosynthesis of individual NPs could easily overwhelm those coming to the subject for the first time. Consequently, this chapter avoids as many details as possible (details can be found easily with an internet search) and will try to provide a simple conceptual framework that can be used to see patterns in the details that are provided by others. 

There are very few major pathways used to generate NP diversity. One can trace the evolution of two major pathways, which account for nearly 90% of NP diversity, back to their microbial origins. 

The ancient pathways that make this chemical diversity benefit the producer in at least two different ways hence, the evolution of these pathways are shaped by multiple selective forces. Some of these chemicals possess potent biological activity while others bring beneficial physicochemical properties to the producer. Consequently, these are multifunctional pathways. 

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