Various amino acids share a few steps on their biosynthetic pathway. Altough, each of these pathways is independently controlled. Escherichia coli does so via different isozymes that respond differently to the different amino acids in terms both of feedback inhibition of enzyme activity and repression of enzyme synthesis. In adition, the pathway direction is controlled by feedback inhibition at the branch points by the individual amino acids.

In the nucleotides synthesis the regulation of branched pathways uses a different strategy.