Central carbon metabolism of S. cerevisiae during aerobic growth on glucose. Gene names in boxes are given for reactions that were identified as flexible by flux balance analysis. Dark gray boxes indicate mutants, for which the carbon flux distribution was determined by 13C-tracer experiments. Dots indicate that the gene is part of a protein complex. Arrowheads indicate reaction reversibility. Extracellular substrates and products are capitalized. C1, one-carbon unit from C1 metabolism.