Our Molecular Nature: The Body S Motors, Machines and Messages

Evolution operates like an origami master at the molecular level, an insight described by David Goodsell with a remarkably simple graphic scheme in "Out Molecular Nature." For all the glib talk about what genetic engineering can or might do, it is not so easy to find anything that explains what it does do, in term available to the non-specialist. Goodsell does it. New genes (whether engineered or evolved) specify new molecules, mostly proteins. Their functions are dictated largely by their shapes. "Many enzymes (proteins that order other proteins around) were developed very early in the evolution of life and have not been substantially improved in billions of years and trillions of generations," writes Goodsell about dihydrofolate reductase, a smallish protein whose job is to move carbon atoms. In fact, only the small "folate" site does the work, and it could not change and still function. The rest of the amino acids that make up this enzyme serve only to fold the folate sector into the proper shape. With at least 60,000 proteins involved in the human body (the count has more than doubled in a generation), it is impossible to keep track of them. Goodsell, a drug designer at the Scripps Research Institute, helps make sense of the mob graphically. He has chosen about 150 of the best understood molecules of life (not all proteins) and drawn pictures of them. The pictures are simple, black, white and gray, and what they convey is relative size and the shape of the active sites. This kind of information is accessible even to a reader with no training in chemistry at all, though of course a sophisticated reader with get more out of it. But, for example, valence number is never even mentioned. Goodsell's little descriptions are packed with out-of-the-way information. Sugars, much misrepresented in the popular press in discussions of nutrition, are dealt with on a more fundamental level here. We learn that, despite the preference of the diet police for fructose over sucrose (cane sugar, which is glucose and fructose combined), the body hardly uses fructose at all. While most of us prefer to eat sucrose, what the body wants is glucose. What little fructose is wanted is manufactured by the body itself, in the sex cells, where its only use is as the energy source for sperm. The secret of life . . . is the ability to build molecules according to need," writes Goodsell. Besides proteins, Goodsell illustrates the nucleic acids, which make the genes that tell the body what proteins to make; and a few molecules that are not proteins. To me, the most fascinating protein is ATP synthase, which Goodsell describes as "a molecular waterwheel." The marvelous thing about this molecule is that tis functional part spins around an axle that anchors it to a cell wall. The push is provided by hydrogen ions (that is, nake protons). This mechanical effort is transmuted into chemical energy, and for each nine protons that pass through, ATP synthase cranks out one molecule of

My take on this book is very different from that of the other two reviewers here at this time. I have read a number of books on this general subject and found this one much better. It is descriptive, as stated in another review, but wonderfully so. As an example (p 87, with drawings): "Cells are sewn together, almost touching, by thousands of connexons at small patches called 'gap junctions'. Each connexon is composed of six identical protein units, together forming a hexagonal tube through the cell membrane. A constant traffic of sugars, amino acids, ATE, and other small molecules travels from cell to cell through them. However, large molecules like proteins cannot pass through these narrow tubes, so each cell retains its own machinery. In times of distress, these tiny knotholes can be sealed. The concentration of calcium inside cells is normally kept very low, so if large amounts of calcium flow through a cell, it is usually a signal that it has been breached. Sensing a sudden rise in calcium, connexons snap shut, isolating healthy cells from a damaged neighbor." One-hundred-and sixty-six pages, packed full of similar descriptions, that in my opinion are well-organized, taught me much more than any other book on the same subject has.