NASA scientists studying the origin of life have reproduced uracil, a key component of our hereditary material, in the laboratory. They discovered that an ice sample containing pyrimidine exposed to ultraviolet radiation under space-like conditions produces this essential ingredient of life. Pyrimidine is a ring-shaped molecule made up of carbon and nitrogen and is the basic structure for uracil, part of a genetic code found in ribonucleic acid (RNA).

An ice sample is deposited in a chamber where it is irradiated with highenergyUV photons from a hydrogen lamp at approximately -442 ºF. Thebombarding photons break the chemical bonds in the ice samples, whichthen form new compounds, such as uracil.
Pyrimidine also is found in meteorites, although scientists still do not know its origin. It may be produced in the final outbursts of dying, giant red stars, or formed in dense clouds of interstellar gas and dust. In theory, the researchers thought that if molecules of pyrimidine could survive long enough to migrate into interstellar dust clouds, they might be able to shield themselves from radiation destruction. Once in the clouds, most molecules freeze onto dust grains. These clouds are dense enough to screen out much of the surrounding outside radiation of space, thereby providing some protection to the molecules inside the clouds.

Scientists tested their hypotheses in the Ames Astro-chemistry Laboratory. During their experiment, they exposed the ice sample containing pyrimidine to ultraviolet radiation under space-like conditions, including a very high vacuum, extremely low temperatures (approximately –340 ºF), and harsh radiation. They found that when pyrimidine is frozen in water ice, it is much less vulnerable to destruction by radiation. Instead of being destroyed, many of the molecules took on new forms, such as the RNA component uracil, which is found in the genetic make-up of all living organisms on Earth.

For more information, visit www.nasa.gov/topics/technology/features/uracil.html

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