hat are you made of? Look at your hands. Draw one palm across the
Feel the density of your tissues, the bones, musculature, and
sinuous ligaments. What gives your tissues substance and form? You have
probably been told that your body is composed of trillions of living cells. But
what are your cells made of? What is the stuff of life?
Those of us hailed by contemporary technoscience are likely familiar with
the notion that proteins are the molecular building blocks of life. But what is
a protein?1 And why do we care so much about the molecular constitution of
our bodies? Proteins are remarkably prominent actors in our everyday expla-
nations of life and health. We so often hear that “you are what you eat.” When
you are hungry, what is it you are looking for? You don’t have to be an athlete,
nutritionist, or dieter to know that protein- rich foods satisfy your hunger. If
you live in the relative privilege of North America or Europe you are unlikely
to escape a consumer culture that finds you constantly on the lookout for
ways to improve your body and your health. Maybe you compulsively read the
nutrition labels on packaged food at the supermarket, those little charts that
fractionate foods according to chemical composition, listing the amounts of
fat, salt, sugar, cholesterol, and protein you are about to consume. How many
grams of protein are in that package of tofu? Or that slice of processed cheese?
Proteins, we are told, provide sustenance. Yet scientists also figure pro-
teins as the enzymes that catalyze life- sustaining chemistry; the substances
that transduce signals within and between cells; the molecules that tran-
scribe, translate, and rewrite Dna to produce more proteins; and the materi-
als that provide the dynamic—continually cycling, growing, and retracting—
architectural support for cellular life. The evolutionary stories we tell ourselves
about the origins of life and the adaptations of organisms rely on knowledge
of heritable changes in Dna that affect the molecular constitution of proteins.
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