1. 1 What is Selectivity? purpose, and crop protective agent for the A
biologically-active substance is said to be second, but there is no
fundamental difference selective if it strongly affects certain cells
with- of principle in their mode of action. out causing any change in
others, even when the Drug therapy has two, fundamentally two kinds of
cells are close neighbours. In living opposed divisions. The first of
these strives to organisms, there are many substances, often improve the
action of one of the cell's natural quite small molecules, which have
been chosen agents by modifying the molecule in order to for their
specificity. This choice has been made localize or intensify its action.
For instance, under the strong pressure of natural selection, the
solubility can be decreased to make it form unhurried by any
consideration of time. Such a deposit, or a change is made so that it
becomes chemical compounds operate the metabolism a poorer fit on the
naturally-occurring destruc- of the cells and tissues, and ensure their
health, tive enzyme. Both of these devices have proved survival, and
reproduction. Important among useful in therapy, e. g. with steroid
hormones. the smaller of these selective molecules are Such drugs, which
seek to improve on Nature vitamins, coenzymes, hormones, neurotrans- by
performing more desirably, are called mitters, inorganic ions,
nutritional fragments, agonists.
