Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [9]
In nineteen tubes nothing happened. The twentieth tube was filled with the amino acid phenylalanine, and only in that tube did new proteins form. Nirenberg and Matthaei had discovered the first entry in life’s dictionary: UUU equals phenylalanine. Over the next few years they and other scientists would decipher E. coli’s entire genetic code.
Having deciphered the genetic code of a species for the first time, Nirenberg and his colleagues then compared E. coli to animals. They filled test tubes with the crushed cells of frogs and guinea pigs, and added codons of RNA to them. Both frogs and guinea pigs followed the same recipe for building proteins as E. coli had. In 1967, Nirenberg and his colleagues announced they had found “an essentially universal code.”
Nirenberg would share a Nobel Prize for Medicine the following year. Delbrück got his the year after. Lederberg, Tatum, and many others who worked on E. coli were also summoned to Stockholm. A humble resident of the gut had led them to glory and to a new kind of science, known as molecular biology, that unified all of life. Jacques Monod, another of E. coli’s Nobelists, gave Albert Kluyver’s old claim a new twist, one that many scientists still repeat today.
“What is true for E. coli is true for the elephant.”
THE SHAPE OF LIFE
With the birth of molecular biology, genes came to define what it means to be alive. In 2000, President Bill Clinton announced that scientists had completed a rough draft of the human genome—the entire sequence of humans’ DNA. He declared, “Today, we are learning the language in which God created life.”
But on their own, genes are dead, their instructions meaningless. If you coax the chromosome out of E. coli, it cannot build proteins by itself. It will not feed. It will not reproduce. The fragile loop of DNA will simply fall apart. Understanding an organism’s genes is only the first step in understanding what it means for the organism to be alive.
Many biologists have spent their careers understanding what it means for E. coli in particular to be alive. Rather than starting from scratch with another species, they have built on the work of earlier generations. Success has bred more success. In 1997, scientists published a map of E. coli’s K-12’s entire genome, including the location of 4,288 genes. The collective knowledge about E. coli makes it relatively simple for a scientist to create a mutant missing any one of those genes and then to learn from its behavior what that gene is for. Scientists now have a good idea of what all but about 600 genes in E. coli are for. From the hundreds of thousands of papers scientists have published on E. coli comes a portrait of a living thing governed by rules that often apply, in one form or another, to all life. When Jacques Monod boasted of E. coli and the elephant, he was speaking only of genes and proteins. But E. coli turns out to be far more complex—and far more like us—than Monod’s generation of scientists realized.
The most obvious thing one notices about E. coli is that one can notice E. coli at all. It is not a hazy cloud of molecules. It is a densely stuffed package with an inside and an outside. Life’s boundaries take many forms. Humans are wrapped in soft skin, crabs in a hard exoskeleton. Redwoods grow bark, squid a rubbery sheet. E. coli’s boundary is just a few hundred atoms thick, but it is by no means simple. It is actually a series of layers within layers, each with its own subtle structure and complicated jobs to carry out.
E. coli’s outermost layer