ABSTRACT
It is at first sight difficult to accept the idea that living creatures are merely chemical systems. Their incredible diversity of form, their seemingly purposeful behavior, and their ability to grow and reproduce all seem to set them apart from the world of solids, liquids, and gases that chemistry normally describes. Living organisms are made of only a small selection of the 92 naturally occurring elements, four of which—carbon, hydrogen, nitrogen, and oxygen—make up 96.5" of an organism's weight. The reactions inside a cell occur in an aqueous environment. Life on Earth began in the ocean, and the conditions in that primeval environment put a permanent stamp on the chemistry of living things. Much of biology depends on the specific binding of different molecules caused by three types of noncovalent bonds: electrostatic attractions, hydrogen bonds, and van der Waals attractions; and on a fourth factor that can push molecules together: the hydrophobic force.
