So how do these two molecules act on different parts of the body, making coffee the substance of choice over chocolate bars when midterm season hits? Caffeine is mostly derived from Coffea Arabica, or coffee beans, and seeds. In the case of caffeine, it turns out that the extra methyl group on the molecule is what makes coffee active on our central nervous systems and an “energy stimulator,” while chocolate functions as a sweet treat and smooth muscle stimulator.įigure 1: During the metabolism of caffeine in the body, the methyl group (highlighted by the yellow box) is removed from caffeine and it is converted to theobromine (Modified from Wolf LK, 2013). For example, additional methyl groups can help a molecule to cross the blood-brain barrier and enter our brain - this barrier protects our brain from foreign molecules traveling in the blood that can be harmful. It may seem simple, but a methyl group is an integral part of chemistry, biology, and biochemistry. At the molecular level, a methyl group is a carbon with three hydrogens attached. It seemed to make sense that as the caffeine I drank was metabolized by removing the methyl group, caffeine would convert to theobromine (the main compound of chocolate) (Figure 1). When my organic chemistry professor told me that the main molecular component of chocolate, theobromine, differs from caffeine only by the absence of one methyl group I was delighted: I could skip an entire step in caffeine metabolism, avoid the bitter taste of coffee, and increase my chocolate consumption. Photo credit: Lisa Townley (left) Pyogenes Gruffer (right), Flickr.
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