Schematic representation of metabolic fluxes upon different carbon sources. Glucose uptake results in fermentation processes via activation of high efficient Pyk1p and thus a rapid turnover of phosphoenolpyruvate (PEP). Inhibition of the pentose phosphate pathway by triose phosphate isomerase causes an increase in NADP⁺, but not in NADPH. High glucose activates Adh1/3/4/5p which forces the formation of ethanol upon fermentation processes. Additionally, glucose represses Adh2p and thus inhibits the vice-versa production of acetaldehyde from ethanol. Ethanol, galactose and glycerol stimulate expression of the less active Pyk2p, which furthermore enhances intracellular levels of PEP. Enhanced PEP leads to an activation of the PPP, increases respiratory metabolism via pyruvate and acetyl-CoA intermediates. Malate is converted to pyruvate by mitochondrial Mae1p and thereby reductive NADPH is synthesized. Upon strict carbon starvation metabolic fluxes are restricted. At the same time, stress response mechanisms and autophagy are induced, which ultimately results in longevity. Factors and processes involved in the promotion of cell death or exerting pro-survival functions are marked in red and green, respectively. Abbreviations: Ac-CoA, acetyl coenzyme A; GAP, glyceraldehyde 3-phosphate; Gal1P, galactose 1-phosphate; G1P, glucose 1-phosphate; G6P, glucose 6-phosphate; Gly3P, glycerol 3-phosphate; GSH, glutathione; NADP, nicotinamide adenine dinucleotide phosphate; PEP, phosphoenolpyruvate; PPP, pentose phosphate pathway; ROS, reactive oxygen species; TCA, tricarboxylic acid cycle.