Microbial growth requires the presence of several complementary nutrients within the growth medium. Each of these nutrients supplies a different nutritional requirement, e.g., carbon or nitrogen. Furthermore, nutrients that supply the same nutritional requirement, i.e., substitutable nutrients or (substrates), may also be present. As the limiting substrate is altered, a microorganism’s internal structure is also altered by preferentially invoking different metabolic pathways for the utilization of the Limiting substrate; Transitions between different pathways are moderated by processes associated with metabolic regulation. The present paper describes an objective-oriented approach to account for such regulatory processes. Ramkrishna and co-workers [Kompala, D. S.; et al. Biotechnol. Bioeng. 1986, 28, 1044-1055; Ramkrishna, D.; et al. Biotechnol. Prog. 1987, 3, 121-126; Turner, B. G.; et al. Biotechnol. Bioeng. 1989, 3 34, 252-261] have developed a cybernetic or goal-seeking modeling perspective that accounts for metabolic regulation in a simple manner by utilizing the optimal behavior of microorganisms when presented with a set of substitutable carbon sources.