ABSTRACT
So far, our journey through the study of circadian physiology has covered the phenomenology of circadian rhythms in Section II and the physiological mechanisms responsible for rhythmicity in Section III. Here in Section IV, we will discuss the physical substrates of circadian rhythms-that is, the cellular and molecular phenomena that underlie physiological processes. We will not go as far down as the level of basic interactions between the chemical elements (Figure 11.1), but we will descend into the labyrinth of that class of organic compounds (DNA and proteins) responsible for the generation of circadian rhythmicity and for life itself.
