G, C, A and T

4 08 2011

“I really had no idea,” Lindenmeyr said. “It’s so…alien.”

The breather unit strapped across her mouth and nose muffled her voice. She stood across from the leading molecular biologist of the colonies. They were standing in a geodesic greenhouse, an igloo of polymers and plastics, connected to Alpha-2’s hydroponics shed by a tented walkway. Regolith had built up on the windward side of the igloo.

The molecular biologist was also head of hydroponics for Alpha-2, Lindenmeyr’s counterpart, and he was an ebullient man in his fifties named Ngan. He ran his hand over a frond of the methanogen. The alien plants were lined in a nutrient trough not unlike the lettuce and soy that Lindenmeyr so delicately tended each day; these plants were, however, immersed in a solution of hydrates, and existed in an atmosphere of carbon dioxide and methane.

“Oh yes,” Ngan spoke eagerly. He chuckled. “Very alien. You don’t know the half of it.”

“Even the name,” Lindemmeyr ventured, “is anthropomorphic.”

“Oh yes.”

Buried deep within Earth’s mantle, microbial communities existed that were almost entirely isolated from the rest of the planet’s biosphere. Within those depths, hydrogen was dissociated from water by heat and pressure and radioactivity, and this hydrogen combined with dissolved carbon dioxide and powered the microbial biomass, which metabolically produced methane. These were the methanogens after which we had, somewhat unimaginatively, named the biomass of Fram.

Lindenmeyr ran her bare fingers through the fronds. The texture of the plant was more like soft rubber, or maybe putty; it offered an unnerving resistance to her touch. On closer inspection, she could see that these fronds were in fact wide, tube-like structures, fatter at their base but which inevitably narrowed into a mouth at the tip.

“The methanogens on Earth,” she said, “they’re microbes. They could be studied only through a microscope. This I can touch, feel, plant.”

“Microbial methanogens,” Ngan said, referring to the Terran variety, “are thermophiles. They thrive on heat. By comparison, these methanogens are psychrophiles. That they live through Fram’s winters speaks to their extreme tolerance of cold.”

“Should we even be calling them ‘methanogens’?”

“I don’t see why not. They produce methane from carbon dioxide and hydrogen, just as their microbial counterparts do. And both are extremophiles.”

“But comparisons end there,” Lindenmeyr prompted.

On Earth, all life emerged from the same soup of primordial microbes, three or four billion years ago. This emergence was the spark of life, a miracle, a random assembly of strings of amino acids into coherent structures that spawned nucleotides, proteins and enzymes – a moment of such unimaginable unlikeliness that humans would later deify it and call it Genesis. From that point, life blossomed and developed and was subjected to the pressures of evolution, and diversified into the branches of the tree of life.

We know that all life came from the same point of origin because all the life on Earth – humans, bacteria, tomatoes, pigeons, everything – shared the same structure and were organised by the same system. DNA and RNA stored information; proteins and enzymes composed structures; adenosine triphosphate (ATP) released energy. Identical genes were found in vastly divergent species – although organised in different structures, humans shared 63 percent of their genetic material with mice and 38 percent with yeast.

From the data stored in DNA, genetic code translated instructions for ribosomes to make proteins by stringing together amino acids in a determined order. The information was stored as molecular units named nucleotides; there were four different nucleotides that were labelled G, C, A and T based on the nucleobases guanine, cytosine, adenine and thymine. What distinguished Lindenmeyr and Ngan from their childhood pets or from the soya they drank that morning were the sequence of those letters. DNA grouped these nucleotides into clusters of three: there were sixty-four different possible triplet combinations that together specified twenty-one different types of amino acids. There was a huge range of possible permutations of nucleotides and amino acids, and it was this range that generated the enormous, diverse, elegant abundance of life on Earth.

All life on Earth used these structures to exist.

“Before we even got to a genetic profile, we knew something was different,” Ngan said. “You know that microbial methanogens use chemiosmosis to generate ATP, where hydrogen is the reducing agent and carbon dioxide is the substitute electron acceptor in the absence of oh-two.”

“Anaerobic respiration, yes.”

“Well, the methanogens on Fram don’t produce ATP through chemiosmosis. At first we thought that they produced ATP through oxidation of carbohydrates, with an endogenous electron acceptor, maybe sulphate…”

“Wait,” Lindenmeyr said. “Fermentation?”

“Oh yes, that’s what we thought. Based on these tube-like fronds and these plants’ preference for carbon dioxide and hydrogen. But it seems that these methanogens, well, they don’t produce ATP.”

“Umm.”

Botanists had subjected the Fram methanogens to the Levin test, a labelled release of two liquids, one of sugars and the other of amino acids. The test was to determine chirality, the preference of genetic material for right-handed sugars or left-handed amino acids. The tests reacted equally to both mixtures, suggesting a chemical rather than biological reaction.

“My god,” Lindenmeyr whispered. “There’s no chirality. No right-handed DNA spiral.”

“No,” Ngan replied. “Because there’s no DNA. No ATP. No nucleotides. This is alien life, Vetsera.”

Lindenmeyr took a moment.

“Even so, it’s pretty god damned alien.”

“Oh yes,” Ngan chuckled. “Let me show you what we’ve learned so far…”

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19 02 2012
A, G, U and X « Orbital Shipyards: Alpha Centauri System

[…] Ngan said to Lindenmeyr: “Let me show you what we have learned so far.” […]

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