Life living in the ‘extremes’
Sierran snow in spring is often tinged pink. The microscope reveals an alga with a large red globule within.
The alga lives in a thin film of meltwater which never gets more than a smidgen above 32 degrees Fahrenheit (water in contact with ice cannot rise above the freezing point) – way too cold for comfort for the passing snowshoer.
Hot springs create pools that host gobs of luxuriant deep-green algae. At one such pool in central Nevada, the water measured 160 degrees Fahrenheit – way too hot for the hikers who’d come for a soak.
Keeping oneself alive takes effort. The molecules of which we’re made have to be continuously broken down, built up, repaired and replaced. We assemble and disassemble molecules with tiny “machines” called enzymes.
Each enzyme machine is a molecule, a cluster of atoms maybe a billionth of an inch across – a human hair is roughly a hundred thousand times wider.
The enzyme literally grasps the molecule it is going to work on – its substrate – and then pulls, pushes, squeezes and twists it, weakening the bonds that hold the substrate together, making the substrate easy prey for other molecules to attack it, ripping it apart or bonding themselves to it.
Lacking fingers, enzymes grasp their substrates much as a computer screen attracts particles of dust with static electricity.
Parts of the enzyme are positive, other parts negative. The pattern of charge on the enzyme molecule mirrors the pattern on its substrate – where one is positive, the other is negative.
Opposites attract, causing enzyme and substrate to bind to each other. Once the substrate is in the enzyme’s grasp, the enzyme goes to work.
The enzyme can grasp its substrate but can’t stalk it. The enzyme must lie in wait for a substrate molecule to come close enough to snag.
Open a bottle of perfume, and, even without a breeze, the fragrance sooner or later makes its way across the room. Molecules of air are in constant motion.
As perfume molecules waft out of the bottle, they’re battered this way and that, usually away from the bottle. Such haphazard, first-this-way, then-that motion, is known in physics as a “drunkard’s walk.”
Batted about in a similar way, a substrate molecule progresses by a drunkard’s walk from one part of a cell to another, until it falls into the waiting clutches of an enzyme molecule.
At room temperature, small molecules are moving at roughly 3,000 miles an hour. They move even faster at higher temperatures, but slower at lower temperatures.
Living just a hair above the freezing point, snow algae must have enzymes that can efficiently take advantage of any substrate that comes its way – it might be awhile before another diffuses over.
Algae living in a hot-pool have a very different problem.
Pain – such as immersing a finger in 160 degree water – warns us of danger. The molecules that are batting the substrate this way and that are also battering the enzymes. The higher the temperature, the more violent the collision. As temperatures increase, collisions become violent enough to bust up the enzyme. The enzymes in the hot spring organisms must be tough, so as to hold together.
Not long ago, most biologists considered life impossible except under the comfortable conditions most of us have come to know and love. But “extremophiles” – organisms that love extreme conditions – are breaking records everywhere we look.
If such organisms can survive the extremes of Earth, might they not survive on other worlds, too?
Alan Stahler trained as a biologist and is an amateur astro-nomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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