Read Online Tower of Glass by Robert Silverberg - Free Book Online

own zone of responsibility. Most of the work at the plant was under the direction of alphas; the entire giant installation employed only half a dozen humans. Each alpha looked as tense as Bompensiero himself.
    Manuel passed first through the rooms where the high- energy nucleotides constituting DNA, the basic building-block of life, were synthesized. He gave half-hearted attention to Bompensiero’s quick, nervous spiel, tuning in only on an occasional phrase.
    “—water, ammonia, methane, hydrogen cyanide, and other chemicals—we use an electrical discharge to stimulate the formation of complex organic compounds—the addition of phosphorus—  
    “—a simple process, almost primitive, don’t you think? It follows the line of the classic Miller experiment of 1952—medieval science, right down there on the floor—
    “—the DNA determines the structure of the proteins in the cell. The typical living cell requires hundreds of proteins, most of them acting as enzymes, biological catalysts—
    “—a typical protein is a molecular chain containing about two hundred amino acid subunits linked together in a specific sequence—
    “—the code for each protein is carried by a single gene, which in turn is a particular region on the linear DNA molecule—all of this of course you must know, forgive me for restating such elementary material, forgive me, I only wish to—”
    “Of course,” Manuel said.
    “—and here, in these vats, we make the nucleotides and join them into dinucleotides, and string them together to form DNA, the nucleic acid that determines the composition of—
    Lilith, from those vats? Lilith, from that stinking brew of chemicals?
    The car drifted smoothly forward. An alpha supervisor departed; another alpha, bowing stiffly, smiling fixedly, entered.
    Bompensiero said, “We design the DNA templates, the blueprints for the life-form we wish to create, but then the task is to make the living matter self-replicating, since surely we cannot build an android cell by cell ourselves. We must reach what we call the takeoff stage. But naturally you know that the DNA is not directly involved in protein synthesis, that another nucleic acid acts as an intermediary, RNA, which can be coded to carry the genetic messages laid down in the DNA—
    “—four bases or chemical subunits, arranged in varying combinations, form the code—adenine, guanine, uracil, cytosine—
    “—in these vats—you can almost imagine the chains forming—the RNA transmits the DNA instructions—protein synthesis is conducted by cellular particles called ribosomes, which are about half protein and half RNA—adenine, guanine, uracil, cytosine—the code for each protein is carried by a single gene, and the code, inscribed on messenger-RNA, takes the form of a series of triplets of the four RNA bases—you follow?”
    “Yes, certainly,” said Manuel, seeing Lilith swimming in the vats.
    “As here. Adenine, adenine, cytosine. Cytosine, cytosine, guanine. Uracil, uracil, guanine. AAC, CCG, UUG—it’s almost liturgical, isn’t it, Mr. Krug? We have sixty-four combinations of RNA bases with which we can specify the twenty amino acids—quite an adequate vocabulary for the purpose! I could chant the whole list for you as we travel this hall. AAA, AAG, AAC, AAU. AGA, AGG, AGC, AGU, ACA—”
    The alpha who was traveling with them at the moment coughed loudly and clutched his waist, grimacing.
    “Yes?” Bompensiero said.
    “A sudden spasm,” said the alpha. “A digestive difficulty. Pardon me.”
    Bompensiero returned his attention to Manuel. “Well, no need to run down all the sequences. And so we put together the proteins, you see, building up living molecules in precisely the way it happens in nature, except that in nature the process is triggered by the fusion of the sexual gametes, whereas we synthesize the genetic building-blocks. We follow the human genetic pattern, naturally, since we want a burn an-looking end product,