Nutrient sensing is a cell's ability to recognize and respond to fuel substrates such as glucose. Each type of fuel used by the cell requires an alternate pathway of utilization and accessory molecules such as enzymes and cofactors. In order to conserve resources a cell will only produce molecules that it needs at the time. The level and type of fuel that is available to a cell will determine the type of enzymes it needs to express from its genome for utilization. Receptors on the cell membrane's surface designed to be activated in the presence of specific fuel molecules communicate to the cell nucleus via a means of cascading interactions. Nutrient receptors are receptors that are primarily designed to perform the function of nutrient sensing, whereas other receptors (e.g. insulin receptors, leptin receptors) are extensively multifunctional and perform many functions besides nutrient sensing.[1] In this way the cell is aware of the available nutrients and is able to produce only the molecules specific to that nutrient type.