Caffeine

Molecule of the Week XI

Caffeine -- America's most popular recreational drug -- stimulates the central nervous system. Caffeine consists of two carbon/nitrogen rings with oxygen and methyl groups as substituents. The fused rings are similar to those in adenine (a component of DNA, ATP, and cyclic AMP) -- only the substituents differ. Cyclic AMP and caffeine have similar structures, which is of importance in caffeine's stimulant action. Furthermore, the electrostatic potential around the two molecules is similar. This shows that the molecules are likely to bond in similar places. The molecular orbitals of caffeine and cyclic AMP are also similar in the regions where they have isomorphic structures.

There are four ways in which caffeine stimulates the nervous system. Of these, one is of primary improtance. Another has some level of importance, and the other two only occur at unrealistically high levels of caffeine in the body.

The first of these methods, and the most important, is blocking adenosine receptors. As caffeine has a similar structure to the adenosine group, but also has more heavily electrophilic and nucleophilic functional groups than adenosine (as, for instance, seen in cyclic AMP). This means that caffeine will fit adenosine receptors as well as adenosine itself will. Thus, cyclic AMP remains active, rather than being broken down.

Second among the effects of caffeine is phosphodiesterase inhibition. The phosphodiesterase class of enzymes includes a number of enzymes responsible for breaking down cyclic AMP, thus depriving the body of an energy supply. Caffeine fools phosphodiesterase into attacking it instead, which inhibits the breakdown of cyclic AMP. However, the concentration of caffeine required for this effect to become significant is sufficiently high that the adenosine blocking remains the dominant factor.

The other two laboratory effects of caffeine have been judged insignificant in actual biochemical situations.

Ultraviolet spectrum of the caffeine molecule.

[References #1, #2, #3, #4.]

http://www.courses.fas.harvard.edu/~chem20/caffeine.html