ultimately generate a response, the body uses different cells in the taste bud that each express a receptor for the perception of sweet, sour, salty, bitter or umami. Downstream of the taste receptor, the taste cells for sweet, bitter and umami share the same intracellular signalling pathway. Incoming sweet molecules bind to their receptors, which causes a conformational change in the molecule. This change activates the G-protein, gustducin, which in turn activates phospholipase C to generate inositol trisphosphate (IP3), this subsequently opens the IP3-receptor and induces calcium release from the endoplasmic reticulum. This increase in intracellular calcium activates the TRPM5 channel and induces cellular depolarization. The ATP release channel CALHM1 gets activated by the depolarization and releases ATP neurotransmitter which activates the afferent neurons innervating the taste bud. Cognition The color of food can affect sweetness perception. Adding more red color to a drink increases its perceived sweetness. In a study darker colored solutions were rated 2–10% higher than lighter ones despite having 1% less sucrose concentration. The effect of color is believed to be due to cognitive expectations. Some odors smell sweet and memory confuses whether sweetness was tasted or smelled. Historical theories The development of organic chemistry in the 19th century introduced many new chemical compounds and the means to determine their molecular structures. Early organic chemists tasted many of their products, either intentionally (as a means of characterization) or accidentally (due to poor laboratory hygiene). One of the first attempts to draw systematic correlations between molecules' structures and their tastes was made by a German chemist, Georg Cohn, in 1914. He hypothesized that to evoke a certain taste, a molecule must contain some structural motif (called a sapophore) that produces that taste. With regard to sweetness, he noted that molecules containing multiple hydroxyl groups and those containing chlorine atoms are often sweet, and that among a series of structurally similar compounds, those with smaller molecular weights were often sweeter than the larger compounds. In 1919, Oertly and Myers proposed a more elaborate theory based on a then-current theory of color in synthetic dyes. They hypothesized that to be sweet, a compound must contain one each of two classes of structural motif, a glucophore and an auxogluc. Based on those compounds known to be sweet at the time, they proposed a list of six candidate glucophores and nine auxoglucs. From these beginnings in the early 20th century, the