The Vital Question: Energy, Evolution, and the Origins of Complex Life. By Nick Lane. New York, NY: W. W. Norton, 2015. 368 pages. $27.95.
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The force that through the green fuse drives the flower drives my green age.
Proteins are assembled on remarkable nanomachines found in all cells called ribosomes. (You have 13 million ribosomes in a single cell from your liver.) On the scale of atoms they are massive. They draw in the code script that encodes a protein and translate it into amino acids, making about ten a second, building the whole chain in less than a minute.
—Nick Lane, biochemist, and author of The Vital Question
How, I wonder, can anyone peer this deeply into a single cell, and yet for physicists, who are flocking into biophysics, biology may offer a welcome change of scale. Rather than searching for elusive particles of dark matter, they can confront the spliceosome, nanoscissors that excise introns—noncoding genes—from messenger RNA before the genes arrive at the ribosomes to be turned into amino acids and then into proteins.
Introns—sometimes called junk genes—are found in all eukaryotic genomes—that is, in the genomes of plants and animals composed of nucleated cells as opposed to archaea and bacteria, the other two branches of life that preceded eukaryotes by billions of years and continue to live with and around us today. A gene that is involved in cell metabolism is found in humans and in other eukaryotes as different as mushrooms and seaweed, and even more surprising is that introns are inserted in exactly the same position in hundreds of shared genes. Lane sees this as evidence that these noncoding genes, which make up the greater part of the genome, are the result of invasion of bacterial genes soon after the origin of the eukaryotic cell.
The biologist Max Jacob once said, “The dream of every cell is to become two cells,” but Lane presents the theory that complex life got its start when two cells became one cell because an archaea cell swallowed a bacteria cell, and rather than digesting it, benefited from its energy-producing as we benefit from the mitochondria in every cell of our bodies. In l967, Lynn Margulis recognized the importance of endosymbiosis and argued that mitochondria, which still have some of their own genes, were once free-living bacteria.
Mitochondria, inherited only from the mother’s egg, are used to trace our ancestry. “Our mitochondrial power plants are as vital as our inherited genes.” They are, says Lane, the sites of cellular respiration. It is here that ATP synthase, a protein nanoturbine uses electrons to move protons across a membrane and create ATP, the energy currency used by all living cells, even the odd bacteria that take their electrons from hydrogen rather than oxygen. “The detailed mechanisms of energy harvesting turn out to be conserved as universally across life as the genetic code itself.” That ATP (adenosine triphosphate) became the elixir of life is, I suppose, as accidental as the selection of nucleobases like guanine and adenine for the genetic code.
The title of the Guardian review of The Vital Question is “We Are Built from Voltage.” And the meter reading by biologists is astounding. “A single (human) cell,” says Lane, “contains hundreds of thousands of mitochondria. Their job is to pump protons. Every second the mitochondria in ten trillion cells in the body pump nearly as many protons as there are stars in the known universe.”
Thinking about the cosmos of my own body, I am torn between gratitude that my cells are continually reproducing, and wondering how I can adequately represent in my person all this internal industry, these processes refined over millions of years.