NOVELTY - A data structure (I) relating several Saccharomyces cerevisiae (SC) reactants to several SC reactions, where each of SC reactions includes a reactant identified as a substrate of the reaction, a reactant identified as a product of the reaction and a stoichiometric coefficient relating the substrate and the product, is new.    USE - (I) is useful for predicting SC physiological functions, including growth, energy production, redox equivalent production, biomass production, production of biomass precursors, protein, amino acid, purine, pyrimidine, lipid, fatty acid, cofactor or production of a cell wall component, transport of a metabolite, and consumption of carbon, nitrogen, sulfur, phosphate, hydrogen or oxygen. Preferably, SC physiological function is degradation of a protein, amino acid, purine, pyrimidine, lipid, fatty acid, cofactor or cell wall component. The method comprises providing a data structure relating several SC reactants to several reactions, providing a constraint set for several SC reactions, providing an objective function, and determining at least one of flux distribution that minimizes or maximizes the objective function when the constraint set is applied to the data structure. The flux distribution is determined by linear programming. The method further comprises providing a modified data structure, where the modified data structure comprises an added reaction, compared to the data structure, or lacks a reaction compared to the data structure, and determining at least one flux distribution that minimizes or maximizes an objective function when the constraint set is applied to the modified data structure, thus predicting SC physiological function. The method also comprises identifying at least one participant in the added reaction by associating SC protein with at least one reaction. The method further comprises identifying at least one gene that encodes the protein or a compound that alters the activity or amount of the participant, thus identifying a candidate drug or agent that alters SC physiological function. The method further comprises providing a modified constraint set which comprises a changed constraint for at least one reaction compared to the constraint for the reaction in the data structure, and determining at least one flux distribution that minimizes or maximizes the objective function when the constraint set is applied to the modified data structure, thus predicting SC physiological function (claimed). (I) is useful to stimulate different aspects of the cellular behavior of SC under different environmental and genetic conditions, thus providing valuable information for industrial and research applications. (I) is useful as a model to determine the optimal conditions for fermentation performance, such as for maximizing the yield of a specific industrially important enzyme. (I) is useful to calculate the range of cellular behaviors that SC can display as a function of variations in the activity of one gene or multiple genes. Thus, (I) is useful to guide the organismal genetic makeup for a desired application. (I) is useful to predict or validate the assignment of particular biochemical reactions to the enzyme-encoding genes found in the genome, and to identify the presence of reactions or pathways not indicated by current genomic data. (I) serves as a model to guide the research and discovery process, potentially leading to the identification of new enzymes, medicines or metabolites of commercial importance. The methods are useful to determine a phenotype of SC mutant and for identifying a target in a peripheral metabolic pathway.    DETAILED DESCRIPTION - A data structure (I) relating several Saccharomyces cerevisiae (SC) reactants to several SC reactions, where each of SC reactions includes a reactant identified as a substrate of the reaction, a reactant identified as a product of the reaction and a stoichiometric coefficient relating the substrate and the product, is new.    (I) is produced by a process comprising:    (a) identifying several SC reactions and several SC reactants that are substrates and products of SC reactions;    (b) relating several SC reactants to several SC reactions in a data structure;    (c) determining a constraint set for several SC reactions;    (d) providing an objective function;    (e) determining at least one flux distribution that minimizes or maximizes the objective function when the constraint set is applied to the data structure, and if the at least one flux distribution is not predictive of SC physiological function, then adding a reaction to or deleting a reaction from the data structure and repeating the steps if the at least one flux distribution is predictive of SC physiological function, then storing the data structure in a computer readable medium or media.    INDEPENDENT CLAIMS are also included for:    (1) making (II) a data structure relating several SC reactants to several SC reactions in a computer readable medium or media, by the above method; and    (2) a computer readable medium or media (III) comprising (I), where at least one of SC reactions is annotated to indicate an associated gene, a gene database comprising information characterizing the associated gene, a constraint set for several SC reactions, and commands for determining at least one flux distribution that minimizes or maximizes an objective function when the constraint set is applied to the data representation, where at least one flux distribution is predictive of SC physiological function.